VIRGIN ISLANDS

RESOURCE MANAGEMENT

COOPERATIVE



BIOSPHERE RESERVE

RESEARCH REPORT NO.20



A GENERAL REVIEW OF SEDIMENTATION AS IT RELATES TO

ENVIRONMENTAL STRESS IN THE VIRGIN ISLANDS BIOSPHERE RESERVE

AND THE EASTERN CARIBBEAN IN GENERAL



Dennis K. Hubbard

West Indies Laboratory

Fairleigh Dickinson University

St. Croix, U.S. Virgin Islands



Virgin Islands National Park

August, 1987



A GENERAL REVIEW OF SEDIMENTATION AS IT RELATES TO

ENVIRONMENTAL STRESS IN THE VIRGIN ISLANDS BIOSPHERE RESERVE

AND THE EASTERN CARIBBEAN IN GENERAL



1987



BIOSPHERE RESERVE REPORT NO. 20



DENNIS K. HUBBARD

WEST INDIES LABORATORY

FAIRLEIGH DICKINSON UNIVERSITY

ST. CROIX, U.S. VIRGIN ISLANDS



U.S. DEPARTMENT OF THE INTERIOR

NATIONAL PARK SERVICE



AND



VIRGIN ISLANDS RESOURCE MANAGEMENT COOPERATIVE

VIRGIN ISLANDS NATIONAL PARK

P.O. BOX 7789, ST. THOMAS

U.S. VIRGIN ISLANDS 00801



LOCAL CONTRACTING AGENT

ISLAND RESOURCES FOUNDATION

RED HOOK BOX 33, ST. THOMAS



U.S. VIRGIN ISLANDS 00802

(NPS CONTRACT NO. CX-0001-3-0048)



ABSTRACT



This report discusses the impacts of sedimentation on

tropical marine environments. Because of the greater

susceptibility of reefs, the majority of the discussion is aimed

at this specific environment. Included are:



1. A review of the general types of sediment stress that occur in

marine systems.



2. A discussion of the critical parameters that should be

measured in any study of sediment stress.



3. A discussion of sources of sediment stress in the Caribbean,

including examples from within the v.I.. Biosphere Reserve, the

U. S. Virgin Islands and the eastern Caribbean.



4. A more specific treatment of area-wide problems, along with

strategies that exist or should exist to cope with them.



This document is not meant to be an exhaustive review of the

subject. Rather, it is intended to highlight the problems,

provide some reasonable management guidelines, and serve as a

starting point for developing future VIRMC projects dealing with

this important topic. A synthesis such as this will never totally

satisfy the needs of all individuals. Hopefully it can bea

useful reference tool for those interested in pursuing the

problem further.

TABLE OF CONTENTS



ABSTRACT... 0... ee wc cece cere e ewer nerves ec ee eee ew eee eee ees i

TABLE OF CONTENTS........ Bem ee cece ee wre eet eee e eee eens wee aeee ii

LIST OF TABLES.........ccccceesvenes cer ce eee ee eee ce ee ene teas ii

INTRODUCTION. 1... ccc ccc esr c cece essnes cece ec eeee eae eeae . 21

BacKGround... cece cern ccc ces n ences ereneseeseensos wee 1

Statement of the Problem... . ccc cee etter cere eaens woe 2

TYPES OF SEDIMENTATION IMPACT. ...... cc ccccccccerceveces swe seas 4

Smothering........cce008 seme ewe wren rece nr een sesrseseseres &

Shading.........ccesseeec00. eee cer eee tee eee eee eee en eae 6

Scouring and Inhibition of Recruitment..... Cece eee ew eae .» 8



WHAT ARE THE CRITICAL PARAMETERS?.......cccccccccccceccccceseee- AO

Sedimentation Effects on Corals - a General Discussion....10

Important Parameters to Consider.........cccccccrecececeesld



PRIMARY SOURCES OF SEDIMENT STRESS... .....0 ccc ccencsucsenene ...17

Dredging......seceseee sewer eee meee wc eee sens eee r een en nes 18

Upland Development... .. ccc ccc ccc ccc cere cee eee e eee e ren eees 19



GENERAL SEDIMENTATION PROBLEMS IN THE CARIBBEAN..........0000005 21

Land~-Based Development.......c.ccseeeee. Semen ee eee cen eens 22

Port Development... ... ccc cee ccacensons a earns: |



SPECIFIC PROBLEMS AND STRATEGIES... .... ccc ccc c ence ree ccrsanense .26

ProblemS..... ccc ccc cee w ener cccce sce e wee eeee cee wee eee woes 26

Management Strategies..... em mee rere reese reer ence se reset ee dh

Future Goals and Objectives............ meee eee eee aw eenee 35



LITERATURE CITED..... cece vesesace sac c ec eeee wee e eee tenes 0237



LIST OF TABLES



Table 1. Sedimentation data from several marine environments... 9



ii

INTRODUCTION



Background



This is a final report to the Virgin Islands Resource

Management Cooperative (VIRMC)- outlining a number of topics

related to the impacts of sedimentation within the V. I.

Biosphere Reserve (VIBR). Specifically, the tasks initially

outlined include:



1) A review of the literature on the impacts of sedimentation on

tropical marine ecosystems ,;



2) A review and evaluation of USVI and Federal legislation,

policy and programs to control sedimentation in the USVI ;



3) A discussion of the general causes of sedimentation and its

impacts within the V.I. Biosphere Reserve, the JU. S. Virgin

Islands and the eastern Caribbean ;



4) Recommendations on specific watershed management tools that

might be useful within and around the V.I. Biosphere Reserve ;



5) A prioritized list of future research projects that would

address site-specific problems within the VIBR.



This report is divided into two main sections. The first

deals directly with sedimentation as it impacts marine systems

(i.e. items 1 and 3). The primary focus will be on the coral reef

system for two reasons. First, it is probably the most sensitive

and least understood of the nearshore tropical marine ecosystems

(mangroves, seagrass beds and reefs). Second, the focus of the

management strategy within the VIBR with respect to sedimentation

is likely to center primarily around reefs.



The second section specifically discusses the state of

present protection measures with respect to sedimentation. The

focus is on present strategies to stem sedimentation (item 2), as

well as potential management approaches that might be useful to

provide additional protection (item 4). Consistent with. the

embryonic state of our knowledge, the final recommendations must

be somewhat general and cannot be imposed on every site-specific

problem with equal vigor. Nevertheless, it is hoped that they

will provide a useful framework from which to build a rational

management plan within the VIBR.



The following discussions are not intended to exhaust the

subject of sedimentation in the nearshore tropical system. Nor

do they purport to reference all the critical papers on the

subject. The complexity of the process and the poor level of

understanding largely preclude this possibility. Furthermore, the

background of the author, and thus the interpretations of the

available literature; must reflect a physical bias toward the

subject. The primary goal of this report is to help the reader

appreciate the state of our knowledge and the problems upon which

we must focus if we are to understand these complex processes.



Statement of the Problem



The literature dealing with sedimentation in the marine

environment is certainly extensive. However, despite the great

number of papers dealing with the subject, our understanding of

its impacts is still in its infancy. Central to the problem are

two things: 1) the lack of baseline data before sedimentation

events, and 2) the lack of long-term field measurements relating

increasing levels of sedimentation to metabolic processes within

individual organisms.



As an example of the latter problem, several short-term or

laboratory studies (e.g. Thompson, undated; Rogers, 1983) have

demonstrated a surprising tolerance on the part of certain corals

to short-term high doses of sediment. Yet, the literature is

replete with what amounts to post-mortem autopsies of reefs

destroyed by sedimentation during and after dredging in nearby

environments. At the crux of this problem are the differences

between high doses of sediment over a short period (acute stress)

vs. much lower doses on a continuous basis (chronic stress). This

is compounded by the general lack of baseline data on the

condition of various marine areas prior to stress and subsequent

degradation.



This problem surrounds our ignorance of the specific

metabolic processes that occur within potentially affected

organisms as levels of stress progressively increase. For

example, a storm will have a greater impact on a marine

environment that is already stressed by background sedimentation

than one which occurs in pristine conditions. Before we can

understand these cumulative effects, however, we must come to

grips with the organism-level response to individual stresses.



Our attempts to model nearshore marine systems tell an

unfortunate tale of confusion. Aller and Dodge (1974) and Dodge,

et al. (1974) studied sedimentation in Discovery Bay, Jamaica.

They concluded that the small size of the coral heads was an

adaptation to sediment stress whereby smaller colonies would have

a shorter distance to move sediment and clear the colony. Thus

larger heads would eventually die, leaving the size distribution

they observed. In contrast, Maragos (1974 a, b) interpreted the

presence of all larger heads as a reflection of the same sediment

stress. His logic centered around the inability of coral larvae

to successfully recruit under conditions of high sediment load.

Thus, the only corals that remain are those that recruited

successfully prior to the existing conditions of high turbidity.

The above example typifies the problems in dealing

quantitatively with the topic of sediment stress. Either one set

of researchers is wrong about the controls of sedimentation, or

else the controls in the two areas of study are somehow different

from one another. In either case, extreme confidence in our

quantitative understanding of the problem is probably not

warranted. Attempts to model the interactions of tropical marine

systems (e.g. Berwick and Chamberlin, 1985) have raised some

"interesting" possibilities, but unfortunately will do little to

understand the complex nature of the problem until realistic

input data for such models are available.



In this respect, we are really back at the beginning. We

certainly understand that sedimentation is (generally)

detrimental to marine systems at some level. The problem centers

around determining at what level that will occur, and how that

might be incorporated into a rational management scheme that

allows human entry into such fragile areas. Certainly mangroves

are less susceptible to siltation than reefs; in fact, mangrove

systems thrive under some conditions of high sedimentation in the

absence of associated pollutants (e.g. heavy metals). Seagrasses,

while more susceptible to sedimentation than mangrove complexes,

can still tolerate a wide range of turbidity and sedimentation

compared to coral reefs. As coral reefs are probably the

best-represented of the major nearshore systems in the VIBR, and

are profoundly affected by sediments at all levels, they become

the most problematic in terms of management.



This report will first look at the types of impacts typically

occurring during sedimentation events. While seagrasses and

mangroves are considered (although briefly), the main focus is on

coral reefs. The impacts on mangrove and seagrass systems are

more related to direct removal (i.e. dredging, deforestation)

than to indirect sedimentation. Thus, the management strategy

becomes less dependant on understanding a complex

cause-and-effect relationship and more one of strict

preservation. Coral reefs, in contrast, are potentially affected

by any marine or upland activity. They therefore become the most

problematic from a management standpoint, and are the primary

focus of this report.



The following section attempts to generally summarize the

impacts of sedimentation on reefs. The discussion concentrates on

scleractinean corals for three main reasons. First, they appear

to be the most intolerant species present on the reef, and

therefore represent the most critical problem in developing a

management strategy. Second, the experience of the author is

more broadly based with respect to scleractinean corals. And,

finally, the available literature relating sedimentation to

distributions of other organisms is limited and inconclusive.

With respect to the latter point, it probably is safe to say

that octocorals, sponges, crinoids and a host of other organisms

are more tolerant of (and in some instances thrive on)

sedimentation. While it is not intended to ignore the importance

of these organisms on modern reefs, their usefulness in the

context of this discussion is more related to identifying

conditions less favorable to stony coral growth. Thus, their

occurrence is more useful in establishing ambient conditions.

With respect to management, they become less problematic

(although not wholly unimportant) from the standpoint of

preserving water quality.



TYPES OF SEDIMENT IMPACTS



Increased sedimentation can adversely impact coral reefs in

a variety of ways. These include:



1) smothering of the coral by settling;



2) reducing incident light by turbidity;



3) scouring of the coral by bedload transport of primarily sand;

4) inhibiting recruitment by juvenile corals.



Smothering



of all the potential impacts, smothering is probably the

easiest for a layperson to visualize. Dredging next to a reef

suspends sediment and that material is moved in the prevailing

currents until it settles on the nearby reefs. Certainly much of

the damage documented from past dredging projects (Nichols, et

al., 1972; Johannes, 1975; Dodge and Vaisnys, 1977; Bak, 1978;

Taylor and Saloman, 1978) is related to the direct impact of

sediments smothering reef organisms. lLoya (1976) cited similar

references to sediment damage in Australia (Fairbridge and

Teichert, 1948), Johnston Island (Brock, et al, 1966), Hawaii

(Johannes, 1975; Maragos, 1972), Puerto Rico (Kaye, 1959) and the

Virgin Islands (van Eepoel and Grigg, 1970). Impacts due to

increased runoff from the land have been discussed along the west

coast of Puerto Rico by Morelock, et al. (1983). On Algarrobo

Reef off Mayaguez, coral cover is presently below 2%, and is

dominated by Porites asteroides and Montastrea cavernosa. At

nearby Escollo Rodriguez Reef, increased runoff over recent

decades has deposited up to 1 m of fine silt on the backreef and

eliminated all coral cover.



Even those corals that successfully cope with elevated levels

of sedimentation must pay a price in the removal of that

material. Energy must be expended in mucus production, polyp

expansion, or whatever sediment-clearing strategy an individual

organism might employ. Different corals deal with sediment in

different ways. Some depend almost solely upon external physical

energy (e.g. waves and currents) to remove sediment and

therefore, are severely limited in the environments they can

occupy. Some (e.g. Madracis mirabilis) move sediment by ciliary

action, while others rely on polyp expansion or mucus generation.

Madracis mirabilis appears to remove sand by tentacular action

while muddy sediments are moved by active cilia (Bak and

Elgershuizen, 1976). Thus, the state of this particular coral

affects its ability to remove sediments of varying sizes. When

the tentacles are extended, the colony will be more effective at

removing larger particles. During retraction, increased ciliary

action will facilitate mud _ removal, but will impede sand

rejection.



The ability of the reef to clear sediment has been difficult

to quantify. Rogers (1977; 1983) demonstrated the ability of

Diploria strigosa and D. clivosa to tolerate single, coarse

sediment doses of 800 mg/sq cm and daily doses of 200 mg/sq cm

for aperiod of 45 days. Acropora cervicornis also showed

remarkable tolerance to short-term sediment loading. Thompson

(undated) demonstrated a high tolerance of Porites to both

carbonate sand and certain types of drilling mud. In contrast,

Acropora palmata colonies died after single doses of 200 mg/sq cm

(Rogers, 1983), and are likely susceptible to damage at much

lower levels of stress. Bak (1978) felt that the platy form of

Porites asteroides often found at depth on many Caribbean reefs

‘was almost totally incapable of clearing sediment settling on its

surface.



Montastrea annularis, probably the most important

frame-builder in Caribbean scleractinian reefs has exhibited a

wide range of tolerance in different studies. Lasker (1980)

reported an ability to remove up to 16 mg/sq em-day of deposited

sediment. In contrast, Dodge, et al. (1974) inferred a reduction

in coral growth related to sedimentation (their "resuspension" )

rates as small as 1.1 mg/sq cm-day. In this latter study,

however, it was not demonstrated that the sedimentation levels

measured during the 8 days of their investigation were those

necessarily responsible for the long-term growth rates measured

in their coral samples.



The impact of sedimentation on colony size is not well

understood, and cannot be considered as much beyond speculation

at this time. Dodge and Vaisnys (1977) felt that older colonies

are more susceptible to sedimentation than younger colonies as

they have to move sediment a greater distance to effect removal.

Hubbard, et al. (1985) documented a gradual decrease over time

of the growth rate of 100+ year-old Montastrea annularis colonies



in Reef and Fish Bays on St. John. While they attributed the

trend to subtle changes in runoff as the hillsides reforested,

this decrease in growth rate may reflect a response similar to

that described by Dodge and Vaisnys (1977). Maragos (1974a, b),

however, described an opposite effect, whereby coral recruitment

is inhibited by sedimentation. Therefore, older and larger corals

formed prior to sedimentation will dominate on stressed reefs.

There is probably at least some merit to both hypotheses which

together point out the complexity of the problem.



Corals have evolved a complex set of strategies to deal with

increasing sediment stress. These can be important at the level

of the individual organism or the whole colony. At the organism

level, Hubbard and Pocock (1972) related the sediment tolerance

of individual corals to overall colony morphology, calyx

structure and age of the coral. They felt that the more effective

corals would have a greater number of more complex septa (related

to the structural integrity of the skeleton/organism pair),

higher calical relief (i.e. the polyps are elevated above the

surrounding skeleton), V- or U-shaped calical floors anda

lighter skeleton. Bak and Elgershuizen (1976) felt that long

meandroid colonies (e.g. Diploria strigosa, Manicina aureolata,

Colpophyllia natans) would be better at clearing sediment than

those with short, reticulate valleys (e.g. Agaricia agqaricites).



Colony shape and orientation are also important in

determining the ability to shed sediment. Using Agaricia

agaricites, Bak and Elgershuizen (1976) found that the ability of

the colony to clear sediment could be progressively increased by

tilting the coral away from the horizontal. This in fact appears

to be the strategy by which otherwise sensitive species deal

with sedimentation at depth. In Montastrea annularis, they showed

that hemispherical colonies could remove sediment ina fraction

of the time required by flatter morphs of the same coral. Also,

hemispherical colonies were more effective at removing sand,

while flatter colonies had an easier time with mud-sized

sediment. Whether this is a long-term adaptation to the smaller

sediment sizes introduced onto deeper-water corals (i.e. quieter

energy) cannot be said with certainty, but is a tempting

hypothesis.



Shading



In addition to settling on benthic organisms, sediment can

reduce the amount of light reaching the bottom at any given

depth. Inasmuch as a substantial portion of the carbohydrates

required by corals are produced by photosynthetic algae

(zooxanthellae), this raises another potentially limiting problem

for the coral reef. Similar impacts are likely important in

seagrass beds.



Rogers (1977; 1979) clearly demonstrated the impacts of

extreme shading on the corals of San Cristobal Reef in

southwestern Puerto Rico. After 5 weeks of shading by black

plastic, colonies of Acropora cervicornis showed significant

bleaching of coral tissue and reductions in colony-extention

rate. She proposed a relationship between polyp size and

resistance to shading where corals with larger polyps would

likely have a greater dependence on zooplankton and other

in-water food sources. Corals with smaller polyps (A.

cervicornis) were the first to show bleaching, followed by M.

annularis (medium-size polyps) and two species of Diploria

(largest polyps).



There are several excellent discussions of this problem in

the literature. However, none of them establish quantitative

limits above which reefs or other marine systems can be expected

to suffer specific levels of damage. Cortes and Risk (1985)

described a reef system at Cahuita, Costa Rica along which coral

growth (and probably cover) has been gradually reduced due to

increasing development pressure. They cite an increase in the

amount of terrigenous sediment trapped within the coral skeletons

over time as a response to growing agriculture and logging since

the late 50s. Their data on coral growth, however, do not make a

convincing correlation between runoff, reduced water quality and

actual coral-growth rate.



Morelock, et al. (1979) described an environmental shift in

the positions of reef zones within Guayanilla Canyon off the

south coast of Puerto Rico. In the canyon, 18 m is the lower

limit of coral growth, compared to 37 m along unstressed shelves.

Furthermore, the corals within this zone were those typical of

deeper-water environs in other areas, demonstrating an upward

shift in depth zonation under conditions of higher turbidity

(i.e. lower light). Dodge and Lang (1983) related a sudden drop

in coral-growth rate in the Flower Gardens reef in the Gulf of

Mexico with increased turbidity (and light reduction) during

flooding of the Atchafalaya River. Rezak and Bright (1981)

related it to submarine collapse of the underlying carbonate

terrain , dropping the corals to a depth at which light level was

significantly lower. In either case, the effect of lowered light

levels remains a central control of the rate of coral growth.



Roy and Smith (1971) described an area on Fanning Island

(Pacific Ocean) where reefs are surviving (31% cover) under

conditions of high natural turbidity. In turbid areas (3.5 mg/l

Total Suspended Solids - TSS) coral cover was reduced to 31%

compared to 62% in less turbid areas (1.0 mg/l TSS). This was

accompanied by a shift in the importance of ramose corals in

turbid water (50%) compared to clear water (10%). Based on their

observations, they placed light attenuation at the top of the

list of impacts, followed by smothering and larval inhibition by

burial. Once again, however, there is some question as to whether

the conditions measured during the brief study period were in

fact those responsible for the differences observed in the coral

population. Nevertheless, changes in turbidity at some level

emerge as important controls of reef development.

The critical question in this regard relates to the effects

of specific levels of turbidity on various reefal organisms.

Table 1 summarizes turbidity and sedimentation rates drawn from

several literature sources. It appears that levels of TSS in the

range of 1-2 mg/l can be considered as "normal" on most reef

systems. Instances of reduced coral cover appear in areas where

total suspended solids reach 3-5 mg/l over extended periods of

time. Rogers (1982) did report storm-related turbidity levels of

10-30 mg/l on St. Thomas, however, with little environmental

damage. Once again, these data together point to an ability for

marine systems to tolerate significant short-term perturbations

in water quality, while being relatively intolerant of much lower

but chronic stresses.



Rogers (1979) reported reductions of light levels in 2 m of

water to less than 65 microeinsteins/ sq m - sec. These

conditions corresponded to TSS values of 9-16 mg/l. Decreasing of

the TSS levels to 1.4 mg/l resulted in an order-of-magnitude

increase in light level to 700 microeinsteins at the same depth.

If these levels of TSS are reasonable indicators of reef

responses to sediment stress, then minor shifts in the water

quality of a reef system over a long period of time would appear

to have a very profound impact on reef structure. Certainly this

is not good news to those interested in protection of reefs from

impending stress. What is yet to be established, however, is

whether these levels of suspended solids are those responsible

for the observed patterns of reef development. At a minimum,

long-term measurements of water quality in these areas are

needed. These would provide a more reasonable estimate of the

present conditions associated with these environments. Even more

useful would be historical data on water quality and reef

character, but these kinds of information are essentially

nonexistent.



gcouring and Inhibition of Recruitment



The impact of scouring on corals is more likely related to

the occurrence of bedload (i.e. sandy) transport. Therefore, this

is probably more important as a natural control in areas adjacent

to sand-dominated systems. For example, reefs close to the beach

are often characterized by corals sitting on pedestals that

elevate the main colony from the prevailing traction carpet of

shifting sediments. Likewise, the dominance of A. palmata on many

reef crests is likely a response to the energetic sand transport

over the reef surface. By growing rapidly upward, this branching

coral can quickly attain a position above the zone of periodic

scour by shifting sands. There are other competitive strategies

Table 1.



LOCATION

Costa Rica



Grand Cayman



San Cristobal, PR

Guayanilla, PR

Punta Ventana, PR



Round Reef, Cstd, STX



Long Reef, Cstd, STX



Christiansted, STX



Limetree Bay, STX

Florida. Keys

Discovery Bay, Jam.



Negro Bank, PR



Fanning Is.

Discovery Bay, Jam.

Virgin Gorda, BVI



Brewers Bay, STT



Sedimentation



data from several marine environments.



ZONE



outer crest

inner crest

lagoon



bay



rivers

general reef

general reef

canyon

canyon

backreef

forereef

east tip



w. forereef

e. forereef

backreef

general

general

general

general



e reef (steep)

w reef (flat)



turbid lagoon

clear lagoon

open ocean



backreef



general



grassbed



TSS(mg/1)



0.3-4.6

1.4-18.8

0.2-36.6

2.8-54.0

1.4-6200

0.1-2.4

0.8



4.5-6.1



11-17



OoOrw

wooa



0.9-2.2



SETTLING (mg/cm-da)



12.8-1180



10.0 (1-21)

1.1-9.8



2.3



3-247



0.5-1.1



3-5

15



<imm/yr



0.5-1.1



0.1-1.4

in this rapidly growing, branching morphology (e.g. shading), but



growing out of the zone of sediment scour is probably an

important factor in shallow reef areas.



Likewise, inhibition of larval recruitment can be important.

The effects of this factor are very difficult to quantify,

however. Morelock, et al. (1979) discussed the importance of

substrate type in limiting larval recruitment. The gradual cover

of the substrate by fine-grained sediment or algae limits the

space available for settling. Roy and Smith (1971) cited the

importance of sedimentation to larval recruitment on Fanning

Island, but related it more to the decreased tolerance of the

younger corals to sedimentation. Also, sedimentation increases

(especially from terrestrial sources) are often accompanied by

elevated levels of nutrient input. This favors colonization by

fleshy algae, which further inhibit coral development.



WHAT ARE THE CRITICAL PARAMETERS?



Given that sedimentation can impact corals in many ways, the

problem is reduced to determining how important each of these is

in controlling reef development, and what the critical parameters

that should be measured are. The following section will address

two topics. First, the relative importance of the above limiting

factors in a few example corals will be discussed to illustrate

controls of sedimentation on coral type and zonation. Specific

examples will be used to demonstrate the controls of bedload and

suspended sediments on reef development in natural systems.

Second, an attempt will be made to address the parameters

related to sedimentation that can and should be quantified to

eventually understand sedimentation as a control of reef

development. Some guidelines concerning ways to measure these

parameters and their general usefulness are offered



Sedimentation Effects on Corals - a General Discussion



Of the four effects of sedimentation discussed above,

siltation and light reduction are felt to be the most important.

It is likely that the zonation seen on natural reefs, and

therefore stressed reefs as well, is a response to both of these

factors. Reduced light levels can vertically suppress zone

boundaries (Morelock, et al., 1979; Adey and Burke, 1977).

Hubbard, et al. (1985; in press) hypothesized that a gradual

reduction in water clarity beginning 3-5,000 years ago has

resulted in a progressive decrease in coral cover, diversity and

reef accretion in Salt River submarine canyon on St. Croix.

Likewise, sedimentation can reduce coral cover (Roy and Smith,

1971; Cortes and Risk, 1985) and slow the rate of coral growth

(Dodge, et al., 1974; Rogers, 1982; Hubbard, in press; Hubbard,

et al., 1985).



10

The success of Acropora palmata in the shallow reef zone is

likely related to all the parameters discussed above (reduced

shading, lower sedimentation levels and reduced scour), but

sediment removed by wave action probably sits at the top of the

list. Even low levels of sedimentation have a detrimental impact

on this coral (Rogers, 1977). Changes in Acropora morphology

appear to be some adjustment of the colony to offset the buoyant

lifting forces generated by waves in the different reef zones

(Shinn, 1966).



M. annularis appears to adapt morphologically to levels of

sedimentation, while its growth rate is more a function of light

level (Dustan, 1977; Hubbard and Scaturo, 1985). Bak and

Elgershuizen (1976) showed that hemispherical colonies were more

adept at removing sand found in shallower reef environments,

while platier colonies occurring in deeper water were better

adapted to removing finer particles. Hubbard, et al. (1985) cited

the occurrence of knobbier forms of this coral in higher-stressed

areas of Fish and Reef Bays on St. John as a possible adaptation

to sediment loading.



Agaricia aqgaricites demonstrates a poor ability to clear

sediment of any kind, and relies on a high angle with the

substrate to clear sediment (Bak and Elgershuizen, 1976). This

implies that smothering rather than light attenuation is more of

a control in the distribution of this coral.



While excellent examples of sedimentary controls on reefs

can be found in site-specific studies, stress on a given reef is

generally the result of a combination of effects, and the

relative role of each is difficult to quantify. Hubbard (in

press) describes variations in reef development along the north

coast. of St. Croix where increases in the amount of sediment

delivered from upwind shelves result in a progressive degradation

of the reef cover. While bedload sedimentation is invoked as the

primary control, accompanying changes in water quality are

undoubtedly important as well. Adey, et. al. (1977) cited

increased sedimentation along the south shore of St. Croix 9,000

years ago as the cause of a a cessation of reef accretion, but

is was not obvious how much of this was related to sedimentation

as opposed to reduced light levels. A similar situation has

recently been discovered along the shelf-edge reefs of hla

Parguera in southwestern Puerto Rico (Hubbard and Morelock,

unpubl. data), where a present-day head-coral community veneers

an A. palmata reef that stopped accreting, probably 4-5,000 years

ago.



The complexity of the problem should not discourage future

attempts to model sedimentary controls on modern reefs. In fact,

isolation and manipulation of individual controls likely lies at

the heart of solving the problem. It is important, however,

that the researcher addressing sedimentation recognize the



11

degree of complexity involved and not place too much emphasis on

any one factor measured in a field situation. Given that word of

caution, the next section attempts to list primary controls of

sedimentation, and to suggest reasonable ways to measure then.



Important Parameters to Consider



The above sections have dealt with the general stresses

induced by sediment loading and their impacts on reefs and reef

organisms (primarily corals). This section addresses the

parameters felt to be most important in understanding these

impacts on reefs and other marine systems. At the outset, it

should be stated that the factors listed below reflect the biases



of the author, and may not be in agreement with the priorities of

all researchers in the field. :



Concentration of suspended solids ~- Certainly one of the the

most important factors in dealing with sedimentation is the

amount of sediment introduced into the water column. This

parameter is important in determining both the attenuation of

light in the water column and the potential for sedimentation as

material settles over time. Total suspended solids (TSS) are

typically determined by filtering large quantities of water

through pre-washed and pre-weighed membranes (0.45 micron pore

openings are the most common). Requirements for this procedure

include a suitable filtering apparatus, an analytical balance, a

clean drying oven and a controlled (i.e. temperature and

humidity) room in which to weigh and manipulate samples.

Controlled laboratory conditions and extremely careful procedures

are required. for this method; unless the minimal conditions

listed above can be met, the data are nearly meaningless.



Recently, several optical methods have become available for

approximating total suspended solids. These instruments measure

some character of the suspended solids (i.e. reflectance,

scatter, absorption) and report it in digital units. This

methodology has several advantages, including precision and speed

of data aquisition. Profiles of water character can be taken and

used to map changes in the distribution of these parameters

temporally and spatially. While of great value when used

properly, all these methods share one serious disadvantage: they

measure optical parameters affected by suspended particles, but

do not actually measure the concentration of the particles

themselves. Depending on the size, shape and composition of the

suspended particles, optical measures can vary dramatically among

samples of the same concentration of suspended solids.



Nevertheless, these methods can be valuable if two

conditions are met. First, the researcher must establish the

optical parameters that most likely affect the marine organisms

of interest. Unfortunately there is little agreement as to which

of the three parameters listed above is the most critical. Even



12

then, the optical data are likely to relate only to impacts of

shading and not of smothering. Second, the researcher must

"calibrate" the instrumentation with the local sediments. Only by

understanding the "signature" of the various components of the

suspended particle spectrum can optical data be quantitatively

related to values of total suspended solids. It must be further

understood that these calibrations are site specific (i.e.

optical calibrations from a reef/lagoon area in the open ocean

cannot be used to translate optical data into TSS figures off of

a river mouth where sediments have a different character).



Having said this, the author still feels that these optical

methods may show the greatest promise for the future. But, they

will be useful only after the above calibration procedures have

been applied and only if the researcher remembers what he or

she is measuring. Otherwise spatial and seasonal variations in

the composition of suspended solids will likely lead to gross

errors in subsequent interpretations.



At this point, a careful program of successive filtering for

TSS concentration and composition as described below is the most

reliable methodology. This coupled with calibrated optical

methods, however, will greatly increase our ability to monitor

spatial and temporal variations in suspended solids not

logistically feasible using filtering alone.



Settling rate - Along with shading, direct sedimentation on

benthic organisms plays the major role in limiting reef cover. At

the simplest level, the absolute quantity of the material landing

on the substrate is probably the most important parameter in

determining the likelihood of damage due to smothering.



The most common method involves placing some sort of open

container on or near the bottom and collecting material falling

from the water column. While simple in concept, obtaining

reliable measurements is in fact quite difficult. At the heart of

the problem is designing a trap that will duplicate the amount of

sediment that settles, is resuspended, and again settles on the

adjacent bottom. A trap that is too wide at the mouth will allow

scour within the trap to remove previously settled sediment more

easily than it is resuspended from the adjacent substrate

(undertrapping). Conversely, traps too narrow at their mouth

relative to their vertical dimension artificially hold material

within them while sediments on the adjacent bottom are

resuspended and carried elsewhere (overtrapping). Gardner (1980a

and b) evaluated a variety of trap designs, and concluded that a

simple vertical-walled trap with a height-to-width ratio of 2.3

would most closely approximate settling conditions on the

adjacent substrate. This value is based on both field and

laboratory experiments. Baffles were recommended for areas where

highly turbulent conditions might be expected (e.g. upper

forereef).



13

Once a suitable trap design is chosen, the traps are placed

in the field and allowed to collect sediments for some suitable

period of time. Personal experience has shown that some interval

less than a week is desirable unless conditions are highly

uniform temporally. Traps are sealed in situ and returned to the

lab. Filtering of the trap contents. through pre-washed,

pre-weighed filters provides a total weight of trapped material.

Alternately the water can be evaporated from the container, but

correcting for the salt content of the sediments and evaporated

water becomes problematic unless very large quantities of

sediment are trapped.



Qrigin of suspended and settled solids - Matter suspended in

the water column can consist of inert sedimentary debris or more

reactive organic material (e.g. plant and animal fragments,

plankton). Each of these has a different impact on reef

.organisms, and the relative importance of each component must be

identified. Organic matter is often beneficial to the marine

system, whereas sediment almost always produces stress. There are

several ways to differentiate between sediment and organic matter

in the water column. The most common is dissociation of the

organics by some method (chemical additives such as hydrogen

peroxide; ashing of the organics at high temperatures) followed

by filtration and reweighing. Equipment is identical to that

listed above, with the addition of a muffle furnace for

high-temperature ashing.



Character of the sediments - There are two critical

parameters related to the suspended sediments. These are size and

composition. Of the two, size is the most difficult to measure.

In high concentrations, pipette analysis can be used to determine

size distribution. The methodology is described in Folk (1974).

This method is very time-consuming, however, and precision is

achieved only under very carefully controlled conditions.



In lower concentrations, size distribution is extremely

difficult and costly to determine. Coulter counters, originally

designed for blood analyses, have been used effectively, but are

expensive, and preparation is tedious. More recently, particle

counters using a laser beam have become available, but like

any optical instrument, must be "calibrated" against

pipetting to give a reliable size distribution. Nevertheless,

at a cost of around $18,000 they probably represent the easiest

and least expensive means of determining size characteristics

of suspended sediments in concentrations typically found on

reefs.



This is obviously not an inexpensive venture. Unfortunately

it probably lies at the heart of understanding the impacts of

sedimentation on coral reefs and other marine systems. Our

laboratory studies to date have used primarily coarse material

(fine sand) to stress corals. Yet, much (if not most) of the



14

material reaching reefs from distant sources is comprised of silt

and clay.In terms of predicting the dispersion of muddy sediments

introduced into the marine environment, sediment size is critical

as it determines the rate at which material will settle to the

bottom. Thus, trends in water turbidity and settling are

determined by this parameter along with local current

patterns. ,



It is the author's opinion that understanding the control of

sediment size within the mud range will prove to be the most

critical step in ultimately unraveling the sediment-stress

equations. Sediment size determines the nature of the stress

(i.e. light attenuation vs. smothering), the likely mechanism by

which the coral will expel sediment, and the likelihocd «hat the

sediment will carry adsorbed materials detrimental to the

well-being of the reef (e.g. heavy metals).



The other element of sediment character is composition. At

the most basic level, one must consider whether the sediment is

carbonate (i.e. biological) or siliciclastic (i.e. likely from a

terrestrial source). Within siliciclastic materials, the specific

origin of the sediment, especially in the clay range, may have

important implications to the adsorption of pollutants, heavy

metals and nutrients. Observations by the author infer that

corals can expel carbonate mud with greater ease than

siliciclastic mud. While no concrete data can be provided to

support this contention, the author feels that composition of the

muddy sediment in the water column plays a role only slightly

below that of size in determining stress levels.



Carbonate vs siliciclastic content can be determined by

several methods. The most popular is digestion of the carbonate

fraction in dilute (ca. 10%) hydrochloric acid. As in the case of

organic digestion, the filter must be washed, redried and

reweighed. The procedures for organic and carbonate contents must

be done separately.



Composition of the siliciclastic fraction is typically done

by X-ray diffraction. The equipment is available in most mainland

geology departments, but is sufficiently specialized that it

would not be readily available in the Virgin Islands. The U. S.

Geological Survey likely operates an XRD unit in San Juan, Puerto

Rico.



Light levels - One of the easiest measurements to make is

that of light intensity. Numerous instruments are available to

manually or remotely collect light data. Standard methods have

been established to determine light intensity using a reasonably

accurate, photographic light meter. More sophisticated units

(e.g. Licor light probes) are commercially available within the

price range of most local laboratories.



15

Light measurements taken through the water column can give a

valuable picture of the effect of suspended materials. It is

important that these data be taken on at least some sort of

seasonal basis, as spot measurements taken at haphazardly chosen

intervals can give a misleading picture. If a regular program of

light measurements cannot be undertaken, certainly a careful

collection of light data after extreme events (e.g. heavy seas,

rains) can provide valuable information on the range of light

conditions expected in the marine environment of interest.



Within the shallower water depths, data on light spectra may

be useful. At greater depths, however, filtering of the red end

of the spectrum results in somewhat uniform conditions. Spectral

data may eventually prove to be more important than is implied

here, but is is felt to carry a secondary importance to the more

basic parameters discussed above.



Other factors - The above factors represent the primary

parameters that can be measured or manipulated in an effort to

understand the effects of sediment on marine organisms. In

addition, there are several factors that, while still important,

are not easily manipulated. They are nevertheless still important

in affecting to what degree the above parameters might have an

effect, and are worth mentioning.



Water depth plays an important role in determining the

character of a marine system whether under natural or stressed

conditions. Physical energy levels are progressively buffered

with depth. On the positive side, short-term events such as

hurricanes are less destructive in deeper water. On the negative

side, however, lower energy levels limit the occurrence of

organisms that rely heavily on water motion to clear sediment.



The primary importance of depth is related to light. With

increasing water depth, both the intensity and the character of

the light are modified. Absorption and scattering of light

decreases the intensity and narrows the spectrum of the light

reaching the bottom. In a natural system, the pattern of light

intensity with depth in part controls the distribution of many

reef organisms. Sediment introduced into the water column

effectively reduces the amount of light reaching the bottom at

any depth. On a large scale, the vertical compression and

shallowing of faunal zones on the reef can result (Morelock,

et al., 1979; Hubbard, et al., in press). On a local scale, the

depths at which many marine organisms occur can predetermine the

potential for impact due to sedimentation. In shallow marine

systems (d<2m) moderate levels of sedimentation are somewhat

benign from a standpoint of light limitation. Thus, impacts are

limited to smothering and abrasion. In deeper water, however,

many of the organisms are already at or near their lower



16

threshold with respect to light. Thus, environmental damage can

be done by reduced light even when sediment never directly

contacts the substrate.



Current patterns are aiso important in determining the

pathways over which sediment will travel. Whether related to

dredging or runoff, sediment will typically have a direct effect

(i.e. at the point of introduction) and an indirect impact at

some "downstream" site. Critical parameters in predicting the

patterns of sediment dispersal include:



- settling velocity of the suspended sediments



- current speed and direction



diffusive and turbulent spreading of the sediment



- water depth over which the sediments are being spread



~ the character of the bottom over which the plume is spreading

and settling



Antecedent conditions play an important role in determining

the potential impact of marine sedimentation. Certainly an



already impacted area will be more susceptible to damage than one

that is untouched by prior stresses. Thus, a critical management

decision centers around whether an already stressed environment

requires more protection because of its increased sensitivity or

less protection because it is already ina degraded state. Often

this must be a subjective decision.



Ok | DO

‘



Upland character is important in predicting the amount and

type of sediment a marine system might presently be receiving.

While not in the same general category as the parameters above,

understanding the character of the watersheds and coastal areas

adjacent to the marine environment is a Key component of any

rational management plan. This will be discussed in more detail

in the following section.



PRIMARY SOURCES OF SEDIMENT STRESS



There are numerous ways in which reefs can be stressed by

sediment. These include resuspension by boat traffic, hazardous

spills, inadvertent dumping of sediment into ‘the marine

environment (e.g. open-ocean dumping), landfill and a host of

others. The most common problems, however, are related to two

general activities: marine dredging and upland development. While

the importance of the other potential sources of stress should

not be ignored, these latter two represent the most common

assault on the marine environment, certainly in the Caribbean and

likely on a worldwide basis. As they undoubtedly represent the

primary problems from a standpoint of local resource management,

the following discussions will focus on these two activities.



17

Dredging



Probably the most direct and easy to visualize impacts on the

marine environment are related to dredging. Direct impacts are

related to disruption (i.e. removal) of the marine habitat in the

area of excavation. In addition, numerous downstream effects

related principally to shading and smothering by suspended

sediment take on equal importance.



The adverse effects of dredging on coral reefs and seagrass

beds is well documented (Nichols, et al., 1972; Johannes, 1975;

Dodge and Vaisnys, 1977; Bak, 1978; Taylor and Saloman, 1978;

Penn, 1981). The immediate impact on the environment is obvious.

A significant portion of the sea bed is disrupted. Downstream

effects are more subtle and difficult to predict.



Although the area being disrupted is occasionally a reef (e.g.

channel excavation), more typically it is open sediment or

seagrass beds. Although seagrasses are more tolerant of

sedimentation than reefs, they can be smothered given sufficient

quantities of suspended sediments. The general importance of

seagrass beds has been discussed extensively (for review, see

Taylor and Saloman, 1968; Thayer, et al., 1985; Burrell and

Schubel, 1977; McRoy and Helfferich, 1977, 1980). Removal of

seagrass beds can impact stability of the substrate. Furthermore,

the potential for seagrasses to act as sinks for heavy metals

(Faraday and Churchill, 1979; Lyngby, et al., 1982) raises the

likelihood of long-term toxic effects.



Once totally uprooted, seagrass beds will take over 5 years

to recover even under ideal conditions. (Patriquin, 1975; Zieman,

1976; Thorhaug, 1981). While recovery can be accelerated by

transplantation (Phillips, 1976; 1980), direct loss of seagrasses

must be thought of as a long-term disturbance.



Downstream impacts on seagrass beds are harder to quantify

and predict. Likewise, the major impact on adjacent mangrove

systems are related to removal, and stands remaining after

development (both natural and replanted) often appear to be

coping with existing conditions. Since the 60s, the south coast

of St. Croix has come under heavy pressure from industrial

construction and operations. Despite high suspended-sediment

levels over a protracted period of time, expansive seagrass beds

still remain in the area between two major industrial complexes



(VI Marine Advisors, 1984). No estimates o th ri

productivity of that system have been made, nor fave fheks BSSx



any studies of the indirect impacts on other marine organisms

using those grassbeds. Nevertheless, they are existing at

surprisingly high levels of stress from ambient sedimentation

levels.



18

Generally the hardest hit, and therefore the areas of

greatest potential concern, are the reefs. Sediment suspended by

the dredge or poorly managed sediment-receiving areas on shore

can move considerable distances from _ the initial point of

introduction. How far the sediment will travel depends ona

number of factors. These include:



- sediment size (settling velocity)



~ current speed



- water depth



- importance of resuspension downstream



& ON’ ke



Once the dredging has ceased, the potential often remains for

resuspension as the newly dredged area becomes a center for

commercial navigation. The impacts due to this phenomenon are not

trivial, and must be considered in terms of long-term

environmental degradation.



Upland Development



Probably more important in the Caribbean are the impacts of

upland development. Poor land management can result in a

substantial increase in the sediment load delivered to the

shore's edge. One factor that is often ignored and thus makes

terrestrial impacts all the more dangerous is the cumulative

impact of small projects that would be somewhat benign by

themselves. As will be discussed below, a major problem in our

present management and protective schemes is a system that is

set up to evaluate primarily larger projects, while ignoring

smaller ones that can collectively have a great impact.



To better understand the nature of the problem, it is

instructive to first examine examples from Caribbean areas, and

to then discuss some of the factors responsible for damage

document in the literature. Morelock, et al. (1983) related

dramatic increases in sedimentation off Mayaguez over recent

years to urbanization, industrialization and cane agriculture in

western Puerto Rico. Loya, (1976) described the effects of

increased turbidity on the reefs south of Mayaguez, againa

likely response to upland activities. Degraded reefs off

Guayanilla on the south coast of Puerto Rico have had similar

impacts due to nearshore development, dredging and ship traffic

(Morelock, et al., 1979). On St. Croix, industrialization on the

south shore has resulted in substantial loss of habitat

(primarily seagrass and mangrove), and undoubtedly contributes in

part to the poor water clarity along the southwest corner of the

island. All three islands in the U.S. Virgin Islands have come

under increasing pressure from upland development, and this

problem is becoming progressively more acute on St. John, the

least developed of the three.



19

The importance of this problem has been recognized at least

to some extent by the National Park Service on St. John and the

VIBR in that terrestrial sedimentation has been one focus of

VIRMC studies over the past two years. The Park (and the VIBR)

must coexist with adjacent development, and the impacts of these

surrounding activities therefore take on paramount importance in

the formulation of a workable management plan.



Central to minimizing the impacts of upland development on

adjacent marine systems is understanding the factors that control

runoff. An excellent review of the subject at a general level can

be found in Gottfried (1985). Excellent references are made to

worldwide importance of upland erosion (Crosson, 1983: Eckholm,

1976; Brown and Wolf, 1984), the importance of short intense

rains typical of the Caribbean in affecting high rates of runoff

(Suarez de Castro, 1950; Wolman and Miller, 1960; Hudson, 1971;

Roose, 1977) and the effects of land use on runoff (Smith and

Abruna, 1955; Wilson, 1972; Dunne, 1979; Veloz, et al.,, 1985).



Jordan (1972) described decreases in overland runoff in the

U.S.V.I. over the past century, and related them to gradual

reforestation of the island watersheds after the decline of the

sugar cane industry on those islands. On St. John, excellent tax

records compiled by Tyson (report in prep for VIRMC) show

patterns of land use similar to those described on St. Croix by

Jordon (1972). A likely conclusion would be that runoff in

subsequent years showed a similar decline, thereby reducing

stress levels on nearby reef systems. However, Hubbard, et al.

(1985) were not able to relate this supposed decrease in

sedimentation to any measurable change in the growth rates of

Montastrea annularis sampled in Reef or Fish Bays on the south

shore of the island. Short-term impacts on the growth rates of

nearshore corals in Hawksnest Bay were found to correlate well

with construction activity in the watershed, but no long-term

effects could be found.



Crucial to the problem of managing upland development is

understanding the effects of various land-use practices on

sediment runoff, and to be able then to relate elevated

sedimentation levels to specific levels of damage. Gottfried

(1985) agreed with the contention of Dunne (1979) that land use

is probably the primary control of runoff in tropical systems.

Therefore, management of upland development takes on paramount

importance in any management scheme. In this light, potential

land-use problems and management solutions are discussed at the

end of this report. At this point, however, some

discussion of general controls of runoff are in order.



20

Controls of runoff - General guidelines for predicting the

amount of fresh-water runoff (and therefore, sediment runoff) are

provided in the Engineering Field Manual for Conservation

Purposes (Kautz, 1975). The principal controls are:



- watershed area



- rainfall (volume and intensity)



watershed slope



- soil conditions (i.e. is the soil wet or dry?)

- land use



ak OD

{



Deitrich, et al. (1982) summarized the pathways through which

water from precipitation might be cycled:



P = I + OF + AET + SM + GWS + GWR, where:



= precipitation

= water intercepted by vegetation



OF = water flowing over the ground surface

= evapotranspiration

= soil moisture



GWS = potential for groundwater storage



GWR = underground runoff



A discussion of the importance of each of these parameters

is beyond the scope of this discussion. However, some general

comments on some of these factors is instructive. In the Virgin

Islands, evapotranspiration is high, resulting in a significant

loss of water back into the atmosphere during periods between

rains. Thus, much of the water retained in the upland system is

lost before it can be converted to potable water. This lies at

the heart of our local water problem which often takes on crisis

proportions. Typically, the potential for groundwater storage is

moderate to small on all but the largest islands (e.g. the size

of Puerto Rico). This is compounded even further during periods

when antecedent soil moisture is high and most of the rainfall

runs overland to the sea. As a result of these factors, modest

olumes delivered in short but intense bursts on many small

Caribbean islands do little to ameliorate the potable water

problem while causing above-normal sedimentation damage.



GENERAL SEDIMENTATION PROBLEMS IN THE CARIBBEAN



The Caribbean islands (especially in the eastern Caribbean)

share many common problems with respect to land use, water

Management and stress of nearshore and coastel areas. For a

number of obvious reasons, development has and will continue to

be concentrated along island shorelines. This development

includes home construction, hotels, condominiums, port

development and industrialization, to name a few. Each of these

types of development carries with it a peculiar set of stresses,



21

but they all share the common impact of increased sedimentation.

In the case of land-based development, initial sedimentation is

generally related to increased runoff as sites are cleared for

construction. Later on, lower levels of chronic sedimentation

related to permanent modifications of upland drainage pathways

become more important. In the marine environment, stress is

generally related to habitat disruption during dredging and

filling operations, spreading of suspended solids away from the

project site, disruption of previously existing flow patterns in

the area and resuspension of sediments by continual operation of

the new facility. This section focuses on problems occurring

within the U.S. Virgin Islands and the VIBR, but it should be

understood that most of the problems discussed below occur

throughout the region.



Land-Based Development



There are numerous and recent examples of problems with

upland development in the Virgin Islands. As recently as the

spring of 1986, 30 acres of land were cleared for development of

a resort hotel in Davis Bay on the island of St. Croix. Despite

efforts to maintain construction-related runoff, sediment plumes

have been seen after even moderate (ca. 1 inch) rains. Much of

the upland drainage from the adjacent 400 acres has been diverted

into a single watercourse, and the effect of this modification

will have to await the passage of time. It is certain, however,

that if sedimentation becomes a chronic problem in this area that

the Acropora palmata formations to the west (i.e. downcurrent) of

the project will suffer, as they are very intolerant of

sedimentation (Rogers, 1983).



Hotel construction is on the rise on both St. Thomas and St.

John. At the. -Virgin Grand Hotel on St. Thomas, major

modifications to the upland watershed could have adverse impacts

on nearshore coastal waters in the future. On St. John, hotel

construction in Great Cruz Bay has opened a substantial hillside

to erosion with few apparent erosion-control measures. The area

was already modified in the past by dredging, but increased

runoff will undoubtedy have an effect nonetheless.



During October, 1980, ground was broken for the construction

of a hospital at the head of Hawksnest Bay on St. John. Studies

of the corals in the bay fronting the watershed showed a

significant decrease in the coral-growth rates after

post~-construction rains in 1981 and 1983 (Hubbard, et al., 1985).

Prior to construction, more severe rainstorms had produced no

such effects. Fortunately, the impact of construction was

short-lived, and the significant amount of vegetative cover

separating the construction from the ocean somewhat buffered

sedimentation impacts. A gradual increase in water quality and

coral-growth rate followed cessation of construction and gradual

restabilization of at least part of the upland watershed. Were



22

the construction closer to the beach, however, or were it part of

a longer-term project, it is likely that the damage would have

been considerably more severe. .



In the British Virgin Islands, development appears to be

progressing not out of any need for employment, but rather in

response to a growing government need to financially support its

infrastructure. Thus, management is driven by other criteria and

is somewhat more complicated. Development around Roadtown Harbor

has progressed with no apparent plan, and little evidence of

traditional West Indian architecture is readily discerned in new

construction. The proliferation of small homesites, roads to

serve them, dredging in the harbor and hotel construction are all

proceeding at avery rapid pace. On Peter Island, a proposed

18-hole golf course could profoundly alter present runoff

patterns and have far-reaching impacts on the nearshore reefs.



Another significant component of shore-based development is

industrialization. Morelock, et al. (1979) cited this as part of

the reason for increased sedimentation on the west coast of

Puerto Rico. On the south shore of St. Croix, the South Shore

Industrial Complex was developed starting in the 60s, and

continues today. Contained in the complex are two refineries

(Hess and VIRCO) anda major alumina processing plant (formerly

Harvey Aluminum and now Martin Marietta). Over a 10 year period,

many acres of mangrove were either dredged, filled or indirectly

disrupted as part of the project. A declining economy and a need

for local jobs were cited as a rationale for sacrificing the

largest mangrove complex in the Virgin Islands. Ironically,

Martin Marietta is now closed, Hess Oil has drastically cut back

its work force and the recognition that tourist dollars and not

heavy industry are now needed to solve all our financial woes

represents the basis for the latest onslaught on the marine

system - hotel and condominium construction.



The negative impacts of industrialization are shared by many

members of the Caribbean community. Refineries and oil-handling

facilities are located on St. Croix, Puerto Rico, Trinidad, St.

Lucia and Barbados (ECNAMP, 1980). Tourism is on _ the rise

throughout the Caribbean, and will likely accelerate in light of

a strengthening U.S. economy and a rise in world-wide terrorism.

Accelerated development raises the liklihood of poor planning in

the face of a rapid influx of tourists and dollars.



Another Caribbean-wide sedimentation problem is agriculture.

Traditionally sugar cane has been a major crop. throughout the

Caribbean, and presumably nearshore marine environments have

suffered in the past. The fact that Hubbard, et al. (1985) were

unable to relate land-use practices on St. John to long-term

changes in the growth rates of Montastrea annularis raises some

concern over our ability to detect sediment stress in the absence

of adequate baseline data. This method has been very useful in



23

other areas, but either adaptation of local colonies to stress or



some other factor (perhaps an absence of stress) have resulted in

a relatively stable population of this one coral species on St.

John over time.



On some Caribbean islands, sugar cane cultivation continues

today (e.g. st. Kitts, Barbados, Antigua; ECNAMP, 1980).

Elsewhere (St. Lucia, Guadalupe), large-scale agriculture is

based on other crops (mostly bananas and coconuts). On Dominique

agriculture exists at a subsistence level, but the cumulative

impact of individual farmers can still be substantial.



A major problem on St. Croix and many Caribbean islands

centers around clearing large hillsides of brush and forest to

encourage grass. The plots are cleared just prior to the rainy

season to ensure an adequate water supply for the new vegetation.

Unfortunately the flashy rains typically result in wholesale

Slope erosion, loss of valuable topsoil and the introduction of

large volumes of sediment into the marine environment. In 1977, a

large rainstorm deposited a soil delta 60 ft out into Teague Bay

on the north shore of St. Croix. Direct smothering and subsequent

degradation of water quality due to resuspension likely caused

significant damage to the bay ecology. At Salt River, to the

west, a similar event flushed large quantities of suspended

sediments into the bay and onto steep reef environments beyond.

Visibility was reduced to less than 2 m for a period of several

months, resulting in an estimated 20% reduction in live coral

cover. Little was apparently learned from this episode as recent

agricultural clearing near the base of the watershed and plans

for marina development threaten further damage. Further evidence

of indifference to this problem lies in the exemption granted

to agriculture under the Coastal Zone Management Act of 1978.

Under this mandate, all activity within the coastal zone, except

agriculture, must come under the scrutiny of the organization

created by the Act.



Port Development



Other than general upland construction, the most widely

shared environmental pressures in the Caribbean probably come

from port development. In an island community that has

traditionally depended upon the water for transportation,

commerce and communication, opening of further marine-based

connections continues to dominate our thinking. Except now,

instead of small-scale down-island commerce, we are facing tanker

traffic and cruise liners of ever-increasing size.



Port. development shares all the impacts of upland

construction. Unique to port development, however, are:



1 - habitat loss due to dredging and filling

2 ~- long-term degradation of water quality due to resuspension



24

3 - potential pollution from spills and discharges



Between 1966 and 1972 over 0.5 million cubic yards of

sediment were removed from Christiansted Harbor (V.I. Marine

Advisors, 1983). Justifications included creation and maintenance

of navigable channels, creation of new fastland, beach

nourishment and excavation of construction aggregate. Many of the

present harbor-erosion problems are related to construction of

condominiums on land created during that time. In the western

harbor, one complex presently sits 25 m seaward of the natural

shoreline that existed prior to shoreline filling. The occupants

are committed to a long-term program of beach nourishment to

protect their investment. Next door, a costly seawall was built

to stem runaway erosion related to the same problem.



It is difficult to assess the impact of all this activity on

the marine environment as little or no baseline data exist.

Eastern Long Reef and Round Reef certainly support a sparser

cover than do other areas to the east and west. Relating this to

specific events or to sedimentation in general is difficult in

the face of nonexistent data prior to development. Similarly, on

the south coast of the island, water quality is typically poor

near and downcurrent of the South Shore Industrial Complex

(SSIC). While turbidity levels are demonstrably higher than those

upcurrent, there are several lines of evidence that construction

is only in part responsible for the dirty water in the area.

First, turbidity levels are typically elevated in the same area

on aerial photographs prior to construction. Second, the

southwest corners of tradewind islands typically exhibit a

similar pattern in the absence of a readily identifiable

development source. And finally, the presence of Sandy Point

downstream of the development infers a persistent flow of

sediment into this area over a very long span of time. The SSIC

has likely protracted the turbidity problem along St. Croix's

south shore, but the problem is in determining to what degree

that has occurred and how the benthic population has changed as a

result.



On St. Thomas, Charlotte Amalie harbor is coming under

increasing development pressure. Expansion of port facilities in

the western harbor continue as vessel traffic becomes

progressively heavier. Recent dredging to accommodate the S.S.

Norway increased the maximum harbor depth. Port development on

this scale has a host of other problems including pollution,

navigation conflicts, cross uses of the harbor and increasing

density of moored and transient vessels. Sediment damage due to

port creation and maintenance is difficult to assess as little or

no data exist upon which to make an evaluation.



On St. John, Cruz Bay is falling under increased pressure to

accommodate more vessel traffic. Present users include the

National Park Service, small charter operators, local boaters,

various ferries and commercial freight carriers, small cruise .

ships and the V.I. Seaplane Shuttle. Congestion in the harbor has

necessitated plans to move part of the port operation to other

sites, primary among them a small pond to the south. In addition

to the lost sediment-retention function of the pond, the

potential of sediment damage during dredging looms as a major

possibility.



In the British Virgin Islands, increased boating traffic and

construction is raising the need for larger harbors and the

location of suitable sources of construction material. A large

dredging project is presently underway in Roadtown harbor. Plans

are being evaluated to select dredging sites on the eastern end

of the island for extraction of construction aggregate.



Similar activities are occurring throughout the eastern

Caribbean. Port operations in Guadalupe, St. Lucia and Trinidad

all rely on dredging to maintain navigable ports. These

activities undoubtedly continue on a smaller scale throughout the

islands, largely without any real regard for damage to the marine

environment. More examples could be given, but the basic story

would remain the same. Expansion of ports and shore-based

facilities continues throughout the eastern Caribbean to meet the

demands of a spreading technological and tourism base. These

projects are done largely without adequate baseline data upon

which to predict effect or measure impact. These problems are not

limited, however, to poor third-world countries who lack the

technology or the money to properly address the problem. Many of

the best available examples available of unecessary environmental

damage occur within the U. S. Virgin Islands, and the local

government has apparently learned little from past lessons.



The remainder of this report will focus on identifying

elements of the problem that can be addressed at the local level.

Primary development problems are listed, and possible solutions

are suggested. Hopefully, some of these strategies will prove

viable at least within the VIBR, and eventually in the Virgin

Islands and the eastern Caribbean.



SPECIFIC PROBLEMS AND STRATEGIES



Problems



Examples of the general kinds of problems that occur in the

Caribbean region have been discussed above. Also, the types of

concerns that need to be addressed in studying the impacts of

sedimentation in the marine environment have been elucidated.

This section provides a more specific list of the main problems

that exist specifically within the VIBR, but also within the



26

greater Caribbean as well. A discussion of management strategies

follows. Finally, a brief list of possible projects that might

advance our knowledge of sedimentation effects is proposed.



Slope clearing - This represents one of the most significant

problems facing the U.S. Virgin Islands today. Upland contruction

sites are typically cleared with little or no regard for impacts

of runoff. In the rare instances where sedimentation control

measures are required by government agencies, they consist of a

short-term sediment fence, temporary berms or similar

structures. These measures are generally ineffective, poorly

monitored, and do nothing to stem the longer-term erosion

problems once the temporary structures have been removed and the

development goes into operation. The clinic on St. John stands as

our best documented example of this problem. Short-term

degradation was documented (Hubbard, et al., 1985) and was

minimized only by the short duration of the project and the

remaining heavy vegetation in the lower watershed. Larger

construction projects can often clear entire watersheds, and the

potential for impact is much greater.



Agricultural clearing - Similar in impact to

construction-related clearing is agricultural development. Two



additional problems typically make this an even greater problem.

First, clearing is often done just prior to the rainy season,

thus maximizing the potential for sediment runoff. Second, this

activity falls outside the control of Coastal Zone Management

(CZM) and many other agencies created to stem erosion.



Building in watercourses - With the shortage of available

building sites and the steep slopes that dominate most eastern

Caribbean islands, many homesites and commercial developments are

placed in the central valleys to watersheds. Structures placed

along the sides of the valley add to the water and sediment load

within the central gut. Those directly within the gut reduce the

ability of the streambed to retain water and sediment. This can

have significant impacts both within the watershed (increasing

runoff to lower properties) and in the marine environment beyond

(increased sediment load).



Road construction - Generally associated with any sort of

development is the creation of roads and accessways. On steep

slopes typical of Caribbean islands, these scars along hillsides

not only serve as sites of erosion but can aiso provide channels

to facilitate the carrying of eroded sediment to the ocean.



Infilling of coastal ponds - Over the past few decades, there

has been a gradual reduction in the number of coastal ponds.

Reasons include insect control, creation of fastland, and the

ease with which such areas can be converted to level building

sites. Underlying all these is a general disregard for the

valuable functions that these ponds provide. In addition to their



27

direct and varied ecological functions, these ponds typically

serve as sediment sinks and settling basins. Typically these

ponds formed at the entrances to embayments during the most

recent rise of worldwide sea level. Since their formation, these

ponds have been gradually filling with sediment derived from the

erosion of associated upland watersheds. Because sediment is

trapped in the ponds, the nearshore environments are buffered

from the deleterious impacts of intense rains. With the

elimination of the ponds, runoff and sediment are permitted to

drain directly into the ocean.



Coastal and flood-plain clearing - Like the coastal ponds

discussed above, low-lying areas serve to buffer the marine

environment from upland runoff. Although the trapping function of

coastal flood plains is more diffuse than that of coastal ponds,

vegetative cover still serves to slow down water flow and thus

retard the introduction of sediment into the ocean. Clearing of

these low-lying areas minimizes or eliminates their

sediment-trapping ability. In fact, drainage plans usually

incorporate some means of improving the runoff potential of these

areas (see discussion of channelization below).



Clearing of mangroves - Mangroves serve a number of valuable

environmental functions that are sufficient reasons to justify

their preservation. With respect to sedimentation, they serve two

important functions. First, they stabilize the shoreline and

prevent erosion. Inasmuch as they are typically associated with

muddy shorelines, this translates into lower quantities of

fine-grained sediment being introduced into the adjacent bay.

With respect to upland runoff, they again trap sediment and thus

reduce the amount of suspended load reaching seaward environs.

The root structures break up flow and slow down the water coming

from ._ adjacent land areas. This results in localized

sedimentation, lowering turbidity on the open shelf in the short

run and creating protected areas which will further retard runoff

down the line.



Building on filled submerged lands - With the shortage of

flat land along the island shores, dredged material is often used

to artificially extend the present shoreline. This material is

often incapable of supporting the subsequent structures built in

the area, causing costly engineering problems. Equally important

is the greatly increased possibility of erosion and the

subsequent need for coastal defense structures. The inherent

instability of these areas often results in increased

sedimentation offshore.



Opening of coastal ponds for marinas) ~ If coastal ponds are

tempting as future building sites, they are even more in demand

as potential marinas. The already existing water body reduces

the amount of dredging needed, and the cost of the project is

lowered accordingly. As in the case of filling, the trapping



28

function of the pond is compromised. Although the loss of

function is not as complete as in a filled pond (i.e. the marina

will still trap some sediment), the opening to the ocean still

raises the potential for the movement of sediment into the ocean

beyond, especially during periods of heavy rains. Fine-grained

sediments trapped in the marina can necessitate maintenance

dredging at a later date and can be resuspended by powerboat

activity within the marina.



Channelization of water guts in lowland areas — One of the

secondary problems of coastal development is the need to prevent

flooding of low-lying areas. Typically sediment control plans

amount to nothing more than effectively routing runoff around or

through a particular area in some manner that minimizes upland

flooding. While this is an understandable goal from a development

standpoint, it increases the intensity of coastal sedimentation.

A recent CZM permit on St. Croix included a condition wherein the

developer would help to channelize runoff from adjacent

properties. By eliminating periodic flooding in the surrounding

neighborhood, the developer is providing an apparent service to

the community. Unfortunately, the flooding of surrounding

lowlands had prevented sedimentation in Christiansted harbor by

ponding water long enough for some sediment to settle in the

ephemeral pond created by the rains. The desire to protect

personal property is understandable, but the impact on marine

sedimentation occurs nonetheless.



Harbor dredging - Harbor dredging has been discussed in

detail earlier in this report. Direct impacts are related —

primarily to habitat removal. Indirect effects include

downcurrent sedimentation, habitat degradation and long-term

resuspension due to vessel traffic. In areas where seagrasses are

removed, sediments may become unstable even in the absence of

traffic. In areas where reef is removed, the exposure to

increased wave action can likewise result in increased sediment

suspension and shore erosion.



Seagrass removal - The primary physical function of

seagrasses is to stabilize the substrate. In experiments in

Teague Bay on St. Croix, the removal of Syringodium from a small

area of the lagoon allowed sediment that had been stable in

currents over 1 m/ sec to be moved by currents of only 20-30

cm/sec (Hubbard, unpubl. data). Removal of seagrass on a large

scale can result in a significant reduction in water quality as

the fine-grained sediments are gradually winnowed from the newly

exposed substrate. Eventually water clarity improves, but

migration of the margins of the excavated area, especially in the

presence of wave action, can cause the problem to migrate over

time, greatly extending the impact of the initial removal both

spatially and temporally.



29

Coastal defense structures - The main problem with structures

placed in the marine environment is that they change the

prevailing flow patterns in their vicinity. Scour around the

edges of seawalls, jetties and the like can suspend sediment and

cause localized erosion. This is a problem particularly at the

ends of poorly planned seawalls. The most significant impact,

however, is in wave reflection. Walls placed along the beach

cause waves to be reflected seaward, much like a ball off a

billiard cushion. Sediment suspended by the incoming wave is

moved seaward by the reflected wave, and erosion results in front

of the wall. This sediment is moved seaward and onto whatever

might be in the immediate offshore zone. While small in

comparison to problems discussed above, sedimentation related to

wave suspension combined with the potential for disruption during

construction do represent potential problems that will increase

as shore development becomes more prevalent in the islands.



Clearing of upland vegetation - Most of the above activities

in some way remove vegetation, and increased erosion typically

results. In some instances, however, vegetation removal is not

part of a larger construction project, but rather is done solely

for the purpose of improving visual or physical access to the

beach. The removal of dune grass in the mainland U.S. is a prime

example. Locally it is more common for homeowners or developers

to remove grass and shrubs to create more open sand, or to remove

trees because they block their view. This problem is more related

to ignorance, and is therefore more difficult to control.

Nevertheless, the increased mobility of the underlying material

results in beach erosion and the introduction of potentially

large quantities of sediment into the surf zone. The future need

for artificial protective structures adds to the problem.



Cumulative impacts of homesite development - Worth

considering is the relative importance of single, large

development projects vs. several smaller homesites. This is a

hard subject with which to deal quantitatively, as homesite

development can be so variable. Nevertheless, some thought needs

to be given as to whether several homesites developed with

virtually no sediment-retention measures can actually cause more

damage than a larger project which has been forced to implement

at least a poorly-conceived sedimentation control plan.



|

The primary potential for damage is the confidence that small

projects will have small impacts. This is not always the case.

A single homesite in western Reef Bay has had a substantial

impact on slope stability in the immediate area. The actual

impact on the adjacent marine environment has not yet been

quantified, but considerable concern has been raised within the

Park Service. As pressure increases on areas like St. John,

homesite development could potentially play a role



exceeding that of larger development. ,



30

Management Strategies



Typically there are two approaches to mananagement. One

involves education, and the other regulation. Education simply

consists of making people aware of the problems so they are more

sensitive to them in the future. Unfortunately, due to the

advanced stages of the problem and the small likelihood that

developers will be in a frame of mind to be "educated" in the

short term, regulation emerges as the primary tool of the

manager. Past history has shown that with development, education

usually emerges from regulation if only in the sense that the

developers (large and small) "learn" what they can and cannot get

away with. Certainly Coastal Zone Management in the Virgin

Islands has brought to the forefront many of the environmental

issues that concern us today. The presence of legislation and

regulation at least forces the developer to listen, and hopefully

to learn.



Because of the above problems with direct education, the

remainder of this section will deal with legislative and

regulatory approaches to management within the VIBR and the

Virgin Islands in general. Inasmuch as most of the problems

common in the area are related to physical and biological

elements of the region, most of the strategies discussed below

should be useful in the eastern Caribbean as well. What will

differ from island to island is not the strategies that would be

useful in a particular case, but rather the cultural elements of

the situation that make one strategy or another more appropriate

in each instance. The first section addresses legislative and

regulatory options presently open to the territories. The final

discussion suggests additional approaches that might be

considered. General guidelines for the kinds of areas that should

and should not be developed are suggested.



Existing regulations and laws - A number of local laws exist

that can be used to affect marine protection. A paperback volume

available from the Department of Conservation and Cultural

Affairs (Environmental Laws and Regulations of the Virgin

Islands) outlines these, and provides summaries of their

applications. As these are already available in summary form,

only the general areas of protection will be listed here.



Title 12, Chapter 3 provides protection for trees and other

vegetation adjacent to watercourses. Under these regulations

vegetation cannot be removed from any area within 30 ft of the

center of the watercourse or 25 ft from its edge, whichever is

greater. The problem with this law is likely to be inconsistent

enforcement.



31

Title 12, Chapter 5 contains a number of regulations

pertaining generally to water quality. The most applicable

portion relates to the issuance of a water quality certificate

prior to the granting of other related permits (e.g. Coastal Zone

Management permit). Standards for water quality have been

established, and any probability that a project will compromise

these standards theoretically results in a denial of a

certificate, and therefore, a subsequent permit. Included in

these standards are minimum allowable quantities of turbidity.

Degradation from upland runoff is supposedly considered in this

regard. Unfortunately, color and turbidity standards are set in

terms of optical measures, and these will suffer from all the

problems discussed in an earlier section (i.e. the necessary

calibration standards are not yet available). Nevertheless,

there is a set of regulations within which the impacts of upland

sedimentation can be argued. This represents one area where VIRMC

could make a significant contribution.



The most locally significant piece of legislation presently

in existance is the Virgin Islands Coastal Zone Management Act of

1978. This act created an organization to evaluate development

within the coastal zone and a procedure to initiate that

evaluation. It consists of citizen commissions on each island and

a CZM Office which coordinates the activities of all the

commissioners. The Office of Coastal Zone Management falls

within the Department of Conservation and Cultural Affairs.



Like any organization of this type, CZM has been fraught with

problems ranging from understaffing to political pressure from

above. Nevertheless, it remains as the strongest support for

citizen input to local development yet available. The pros and

cons of this organization can and have been argued on many

fronts. To repeat these arguments here would be of little

purpose. Two major problems with the concept of the legislation,

however, bear heavily on the problem of upland runoff and are

worth mentioning. First, agriculture has been specifically

exempted from the process, presumably based on some perceived

tradition. As wholesale clearing of upland areas undoubtedly

constitutes a major problem in the V.I., removal of this activity

from regulation severely compromises the ability of CZM to

protect adjacent marine waters.



The second, and perhaps larger, problem is the two-tier

system built into the legislation out of deference to the role of

Public Works in the prior permitting process. Under this scheme,

the island is divided into a first tier near the water anda

second tier above. Permits in the first tier are issued by CZM.

Permits in the second tier are within the realm of Public Works.

In some instances, the boundary between the two is a reasonable

physiographic feature (e.g. a ridgeline), but altogether too

often it is simply a_ road or similar cultural structure. The



32

problem with this is two-fold. First, the often arbitrary

boundaries can place critical coastal areas in the second tier,

where permits are much easier to obtain. Second, with the small

size of the three islands and the steep slopes, there are

virtually no areas that do not potentially exert great control

on the coastal zones of the Virgin Islands. A proviso does exist

in the Bill whereby CZM can ask to have input in upland projects

that might directly impact the marine environment, even though

they are in the second tier. However, if this inclusion were

taken seriously, few upland projects would escape the careful

scrutiny of the Office of CZM.



In the late 70s, the V. I. Sedimentation Control Plan was

introduced. The most significant contribution of this program was

a series of maps that provided information on watershed areas,

peak discharges and other critical design factors related to

upland development. While useful from a design standpoint, this

data set provides little or no guidance on the volumes of

sediment potentially eroded from these areas, nor are variations

in land use incorporated into the runoff estimates. Given

opinions by several researchers (e.g. Jordan, 1972; Dunne, 1979)

that land use probably plays the primary role in controlling

runoff volumes, the absence of this factor in the predictions

made by the maps is reason for some skepticism. Nevertheless,

these maps do provide a starting point.



Future strategies - Certainly there is tremendous room for

improving the present levels of environmental protection. The

problems of competition between the local needs for economic

improvement and environmental preservation are numerous, and will

not be discussed here. Nevertheless, there are several specific

management recommendations that have merit and could be

immediately integrated into the management of the Biosphere

Reserve. Most of these have wider applicability to the eastern

Caribben as well...



There are several practices that should be either prohibited

or discouraged. These include:



- development in major water courses



- development in watersheds that empty into low-energy

embayments that will have problems dissipating sediments

introduced during heavy rains.



- any dredging within the Biosphere Reserve boundaries



- any removal of seagrasses or mangroves



any filling of coastal ponds



- any large-scale clearing



do iH



Our |

J



In areas where development must occur, certain guidelines

must be provided for the developer. These include:



33

1 - The establishment of a sedimentation control plan. This

should include identification of marine areas sensitive to

sedimentation as well as a thorough discussion of present and

Proposed water and sediment flow to the ocean. Reasonable

measures to guard against runoff during and after construction

(i.e. sediment fences, berms, settling ponds, silt curtains

during dredging, etc.) should be included and described in

detail. It is critical that this plan not be a water management

plan whose main objective is to facilitate the Passage of water

over the property. In fact, the goal of such a plan should be to

retard runoff until it can soak into the ground or sediment can

settle out of suspension. This is typically counter to the

economic interests of any developer.



2 - The encouragement of sequenced development. Recently, 30

acres of watershed were cleared for hotel development in Davis

Bay on St. Croix. Unusual seasonal rains broke through sediment-

retention fences and introduced sediment onto the adjacent shelf.

The developer's answer to allegations was that no project that

clears this kind of acreage can effectively stop this kind of

runoff. This is probably true, and the lesson learned should be

to develop areas in pieces, allowing revegetation of one section

before another is cleared.



3 - The planning and implementation of monitoring schemes. Any

project has a potential for environmental damage. If that damage

is perceived to be high, then some sort of monitoring plan should

be implemented. This approach serves three purposes. First, it

hopefully can identify areas of stress before permanent

environmental damage is done. Second, it establishes a baseline

against which environmental damage can be measured. The

possibility of quantifying damage (and legal responsibility) may

raise the level of consciousness within the development

community and finally, the observations of environmental change

in response to specific levels of stress provide data upon which

to base future project evaluations.



4 - The provision of economic incentives for the developer to

protect the environment. A simple example of this would be to

require a developer to deposit an amount of money into an escrow

account equal to 10% of the anticipated project costs. This money

would serve as a sort of damage deposit which would be used to

offset environmental damage due to violations of the project

permit conditions. If the project is nearly completed as planned

without damage, then this money would be applied to the final 10%

of the project costs. If the developer stays within the

restrictions of his original agreement, then there is no monetary

loss. If there is significant environmental damage or the

developer pulls out of the project, then the money can be put

toward environmental restoration. This example would probably be

impossible to implement in the local V.I. climate of development

panic, but it might work elsewhere in the eastern Caribbean or



34

certainly within park or preserve boundaries where development is

more easily controlled. For this plan to work, the Park Service

(or whoever operates as manager) must fall under the same

restrictions and penalties.



Future Goals and Objectives



Future efforts of VIRMC should center around two elements.

The first is providing baseline data in areas likely to come

under stress. The second relates to establishing some level of

understanding about how individual organisms and systems respond

to different stress levels.



The choice of baseline areas must be based on likely future

environmental pressures, and primary study sites must necessarily

center around those areas that are slated for change. The

importance of "control areas" (i.e. those areas that will remain

natural as a frame of reference) must be recognized, but this

should not be used as an excuse to concentrate on untouched, and

therefore, more scientifically interesting areas.



Understanding environmental change will ultimately center

around studies of the interactions of the stress components with

the elements of each marine system. It is at this level that our

greatest efforts should be concentrated. It is fine to understand

currents, or to trace sediment transport, or to quantify patterns

of runoff in some number of watersheds as has already been done

on St.- John. All of these are important factors but will not

answer the critical questions about levels of stress and their

associated impacts. If we are ever to understand stress responses

of marine systems, we must first assess where impact is presently

- taking place or is likely to occur in the future. After that,

we need to formulate a list of parameters that are most likely

to affect change. Only after completing all these preliminary

tasks, we must compile a plan to measure these parameters and the

responses of the marine environment that result. VIRMC has passed

through a necessary first stage of baseline data gathering. It

has attempted on a localized basis to establish stresses and

impacts. Now is the time to move on to understanding the basic

elements that cause change in the ocean.



In some respects, VIRMC has approached the problem from a

direction opposite to that described above. Rather than

addressing the levels of change, a much greater emphasis has been

placed on establishing the magnitude of "potential" stresses

(e.g. historical analysis of land use; studies of watershed

character) and management. Less emphasis has been placed on

determining where and how much actual impact is and has been

occurring. This approach has assumed (occasionally in error)

that impact is everywhere and measurable.



35

While erring from the basic Plan discussed above, these

early studies were probably necessary. They represented a logical

starting point considering the almost total lack of



background data on the biosphere reserve. But, it is time now to

move on.



With respect to sediment stress, a number of studies would

be useful. Most of these center around characterizing the nature

of sediments being introduced into marine systems and their

impacts on individual corals. For purposes of illustration, one

large-scale experiment will be described, keeping in mind that

the proposed future research objectives will likely have to

consist of pieces of this project conducted by a variety of

individuals.



The experiment would consist of both field and laboratory

studies of corals responding to varying loads of widely differing

sediments. Field experiments would include subjecting marine

organisms to sediment varying in amount, size and composition.

These experiments would be similar to those of Rogers (1977),

with the addition of a better characterization of the sediments

being used. Lethal effects could be determined by simply

observing the corals. Sub-lethal effects would involve

respiration chambers that are now becoming commercially

available. Laboratory experiments would follow a parallel line,

except they would allow more carefully monitored sediment

applications and perhaps a continuous level of stress more

closely approximating natural conditions.



At the same time, a parallel monitoring plan should be

implemented in the field. Reefs near major water guts should be

quantitatively surveyed and a set of basic measurements

established. A protocol should be developed for sampling that can

be followed by a team of observers on short notice. The

following is a partial list of tasks.



1. Baseline survey of selected study reefs near watershed centers

(e.g. Hawksnest, inner Fish Bay; this has already been done on a

limited basis). These surveys should identify specific quadrats

or transects that can be precisely reoccupied. Permanent markers

should be established such that specific areas on the reef (e.g.

individual corals) can be relocated. The level of accuracy on

such a survey would necessarily be much greater than what has

been attempted to date.



2. Selection of the primary channel(s) out of the water course.

At these sites, cross section and flow velocity should be

measured on an hourly basis during rain storms. Water samples

should be taken for characterization of TSS and sediment

character as described in an earlier section.



36

3. Sampling of marine waters near water guts and in the bay

during rains. Surface, mid-water and near-botton (1 m) samples

should be taken hourly at each site. Sample sites should be

placed on a regular grid. The size of the grid would depend on a)

the size of the sediment plume and b) the extent of potentially

impacted marine systems in the bay.



4. Sampling of settling sediments. Traps as described above

should be retrieved on at least a daily basis. Trapped sediments

should be weighed and their size distribution should be

determined.



5. Permanent quadrats/transects should be examined regularly to

detect sub-lethal effects of sedimentation. Field chamber

experiments could be used in conjunction, especially to quantify

shading effects. The logistics of this are substantial, however.



6. Once enough successful field monitoring programs have been

completed, the conditions measured in the field could be

duplicated in the lab. By increasing either the sediment doses or

the duration of exposure, conditions beyond those measured in the

field could be examined.



While the above approach has been described for upland

runoff, a similar regimen could be applied to in-water projects

such as dredging. For this type of approach to yield usable data,

a significant long-term commitment must be made to specific field

sites. Gathering of baseline data is an important first step.

Unless we start to examine responses of marine organisms,

however, our research efforts will never advance beyond

documenting what is lost or destroyed, and our ability to predict

damage will never be realized.



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