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MARINE PROGRESS SERIES Published April 5 Mar. Ecol. Prog. Ser.

REVIEW

Responses of reefs and organisms to sedimentation

Caroline S. Rogers

Virgin National Park, PO Box 710, St. John, USVI 00830

ABSTRACT: Unprecedented development along tropical shorelines is causing severe degradation of coral reefs primarily from increases in sedimentation. particles smother reef organisms and reduce light available for . Excessive sedmentation can adversely affect the structure and function of the by altering both physical and biological processes. Mean sediment rates and suspended sediment for reefs not subject to stresses from human activities are < 1 to ca 10 mg cm-* d-' and < 10 mg I-', respectively. Chronic rates and concentrations above these values are 'hlgh'. Heavy sedmentation is associated with fewer coral , less live coral, lower coral growth rates, greater abundance of branching forms, reduced coral recruitment, decreased calcification, decreased net of , and slower rates of reef accretion. Coral species have different capabilities of clearing themselves of sediment particles or surviving lower light levels. Sedlment rejection is a function of morphology, orientation, growth habit, and behavior; and of the amount and type of selment. Coral growth rates are not simple indicators of sediment levels. Decline of tropical fisheries is partially attributable to deterioration of coral reefs, beds, and from sedimentation. Sedimentation can alter the complex interactions between and their reef . For example, sedimentation can lull major reef-building corals, leading to eventual collapse of the reef framework. A decline in the amount of shelter the reef provides leads to reductions in both number of individuals and number of species of fish. Currently, we are unable to rigorously predict the responses of coral reefs and reef organisms to excessive sedimentation from coastal development and other sources. Given information on the amount of sediment which will be introduced into the reef environment, the coral community composition, the depth of the reef, the percent coral cover, and the patterns, we should be able to predict the consequences of a particular activity. Models of physical processes (e.g. sediment transport) must be complemented with better understand- ing of organism and ecosystem responses to sediment stress. Specifically, we need data on the threshold levels for reef orgarusms and for the reef ecosystem as a whole -the levels above which sedimentation has lethal effects for particular species and above which normal functioning of the reef ceases. Additional field studies on the responses of reef organisms to both temgenous and are necessary. To effectively assess trends on coral reefs, e.g. changes in abundance and spatial arrangement of dominant benthic organisms, scientists must start using standardized monitoring methods. Long-term data sets are critical for tracking these complex .

INTRODUCTION associated with construction of hotels, condominiums, runways, roads, and military installations and with Sedimentation from and runoff constitutes replenishment has destroyed reefs, seagrass one of the biggest potential sources of reef degradation beds, and mangroves (Endean 1976, Jaap 1984, Dahl from human activities in the and in the 1985, Salvat 1987, White 1987). Dredging near coral Pacific (Johannes 1975, Dahl 1985, Rogers 1985). It is reefs and accelerated runoff of eroded soils increase also a serious threat to reefs in (e.g. , thereby cutting down light available for Chansang et al. 1981, Hodgson & Dixon 1988). In the photosynthesis, as well as increasing sediment load on western Atlantic, Caribbean and Pacific, dredging corals. Sediments which settle on coral colonies or

D Inter-Research/Printed in F. R Germany 186 Mar. Ecol. Prog. Ser.

which cause high turbidity while suspended in the from pipeline dredging. Other seagrass beds in column have sub-lethal and lethal effects. were buried by suspended by cutterhead dredg- Sometimes dredging and other activities which ing. Penn (1981) noted that dredging of sand from increase sediments in the water appear to cause only seagrass beds in the Islands did not affect the localized or negligible effects on corals (Brown & How- seagrass beds adjacent to the sites of sand extraction, ard 1985). The dumping of 2200 tons of kaolin () and from the remaining beds helped to cargo from a freighter grounded on a reef in the recolonize the dredged areas. Maragos (1983) reported Hawaiian Islands created large plumes of the sus- that mangroves will not become re-established on pended clay but had no apparent adverse effects be- dredged holes deeper than about l m. We know almost yond a radius of 50 m from the grounding site (Dollar & nothing about the responses of seagrass beds and man- Grigg 1981). Based on a brief qualitative survey, Shep- groves in cases where there is not complete . pard (1980) suggested that dredging and blasting in Excessive sedimentation can adversely affect the Diego Carcia (Indian ) had resulted in a structure and function of the coral reef ecosystem by variable and low coral cover but no reduction in coral altering both physical and biological processes (Fig. 1). diversity. Construction of a boat harbor in actu- The objectives of this paper are to review what we ally resulted in an overall increase in coral cover know about sediment effects on coral reefs and reef because of colonization of harbor surfaces (USACE organisms, to suggest effective monitoring techniques, 1983). In 1979, work began to extend the runway of the and to identify areas for further research. Knowledge of airport in St. Thomas (U.S.Virgin Islands) 726 m into the precise effects of sedimentation is limited because water 27 m deep. Monitoring of fish populations, - of a lack of direct research. To date there has been no grass beds and coral reefs in the vicinity, over a 31 mo rigorous, comprehensive, before, during, and after period, revealed no significant deterioration attribut- study of the effects of dredging or terrestrial runoff on able to the plume from the dredge and fill operations the structure and function of a coral reef. Quantitative (Rogers 1982). Sediments are less likely to cause a data are scarce and much of the evidence of coral problem when strong currents are present as in this damage from sediments is circumstantial. At times, case. In some of these studies, more detailed or longer excessive sed~fnentationis just one of many stresses investigations might have revealed detrimental effects. affecting a reef, making it difficult to differentiate the Decline of tropical fisheries, evident for the Carib- response to sediments from that to fresh-water, sew- bean (Rogers 1985) and the Pacific (Dahl 1985) is at age, or drilling-fluid components (Pastorok & Bilyard least partially a result of degradation of coral reefs, 1985). This review addresses our current inability to seagrass beds, and mangroves from sedimentat~on. adequately predict the consequences of increasing Increases in sedimentation rates can also alter the sediment concentrations and rates of accumulation in interactions between organisms and their . marine at a time of unprecedented development Juveniles of many fish species and other organisms in tropical coastal areas. depend on mangroves and seagrass beds for food and shelter, moving to deeper waters and offshore reefs as they mature. Deterioration of any of these ecosystems SEDIMENTATION: ECOSYSTEM LEVEL EFFECT can lead to a decline in fish populations. Cutting of mangroves trees which normally entrap sediments can. Dredging result in excessive for nearby seagrass beds and reefs from runoff after heavy rains. Destruction of The purpose of dredging is to obtain sand and corals red mangroves with submerged prop roots decreases for building materials or beach replenishment and to the habitat for juvenile (Thayer et al. 1987). deepen na\igation channels and harbors (DuBois & Excessive sedimentation can affect the complex food Towle 1985). The magnitude and nature of the effects web on the reef by killing not only corals, but also of dredging vary substantially depending on the equip- or other organisms which serve as food for ment which is used (DuBois & Towle 1985, Salvat commercially important fish and shellfish. 1987). We know little of the effects of sedimentation on Dredging often affects not only the portion of the reef tropical marine systems other than coral reefs. Con- which is actually removed or smothered but also down- struction of airport runways led to burial of reefs and stream areas where currents carry increased concen- seagrass beds in Hawaii (Chapman 1979), Truk (W trations of fine suspended particles. Continual resus- Pacific) (Amesbuq et al. 1978) and Kosrae (W Pacific) pension and transport of dredged sedlments can cause (Maragos 1983). At Kosrae, Maragos (1984) noted reef degradation after dredging ceases (Brock et burial of seagrass beds and reefs under up to 0.5 m of al. 1966, Grigg et al. 1972, Marsh & Gordon 1974) For fine slurry muds that accumulated above m.ean low example, dredging and filling destroyed 440 ha of reef

188 Mar. Ecol. Prog. Ser. 62: 185-202, 1990

at Johnston and resulted in siltation which Runoff adversely affected 6 times thls area (Brock et al. 1966). In , Dodge & Vaisnys (1977) attributed The amount of fresh-water runoff which enters the lower amounts of living coral in Castle Harbor relative water will depend on (1) watershed size and slope, (2) to other study reefs to extensive dredging 35 yr earlier. volume and intensity of rainfall, (3) soil condition, and DiploJYa Iabyrinthiforrnis was more abundant than D. (4) land use (Hubbard 1987). Turbidity from runoff stn'gosa, although the 2 species had been more evenly reduces the light available for photosynthesis by mac- distributed before dredging. Hubbard & Pocock's roscopic and turf and endosymbiotic zooxanthel- (1972) laboratory studies suggested that D. labyrinthi- lae within the tissues of corals, anemones, and other forrnis is more capable of rejecting sediments than D. organisms, thereby affecting the overall of stngosa. Dodge & Vaisnys (1977) suggested that larger a coral reef. Rogers (1979) demonstrated that artificial corals are more susceptible than small ones to damage shading of a portion of a reef in Puerto Rico, a partial from smothering by sediment particles because seh- simulation of extreme turbidity, resulted in bleaching ment removal from the colony surfaces is random and of cem'cornis, labyrinthiformis, and uncoordinated, resulting in a greater probability that Montrastrea annularis colonies, a reduction in the particles would remain on a larger colony. growth rate of A. cervicornis, and a decrease in pro- 's reefs are deteriorating partly as a result of ductivity. Some growing tips of A, cervicornis intense economic for upland development disintegrated. and beach replenishment (Jaap 1984, Voss 1988). Few detailed scientific assessments of the effects of Dredging, chemical and thermal are all con- runoff on coral reefs are available. In some cases, it is tributing to the demise of the reefs. In the in difficult to determine if death or bleaching from loss of the 1960s and 1970s, numerous waterfront channels is a response to sediment particles or to were dredged to obtain fill to elevate low-lying coastal . Excessive rainfall during a 1965 in areas for home construction. The dredge plume from Hawaii led to death of reef organisms from a combina- one of these projects, off , resulted in turbidity tion of high turbidity, low salinity, and other factors levels above 200 mg 1-' (Griffin 1974). The largest (Banner 1968). Increased runoff after Hurricane Flora dredging projects now occurring in Florida are for beach led to bleaching of corals, zoanthids, and sea anemones replenishment. Blair & Flynn (1988) quantified exten- in shallow water off Jamaica (Goreau 1964). Increased sive mechanical damage to reefs from the drag head of river discharge may be responsible for the less than 2 % the dredge used to obtain sand for the Sunny Isles Beach coral cover on Algarrobo Reef off the west of Restoration Project in southern Florida. The drag head Puerto Rico and for the accumulation of which was repeatedly pulled across the reefs adjacent to the lulled all corals on a nearby reef (Morelock et al. 1983). sand deposits, resulting in some places in a damage tract of the shoreline and runoff from hillsides can up to 20 m across within which all benthic organisms result in the filling of shallow reef areas and the were basically destroyed. At 2 sites a total of about smothering of corals. The shoreline apparently ex- 6000 m2 of reef was devastated. Marszalek (1981) sur- tended 2 km across the reef in one Hawaiian veyed reef areas before and after a large-scale dredging because upland erosion was accelerated by farming project off Florida and found that sea whips and other (Moberly pers. comm. cited in Johannes 1975). Some- gorgonians were the most tolerant of the reef times, apparently flourishing coral communities are mostly because their morphology prevented accumula- found in naturally turbid conditions. For example, a tion of sediments. No mass mortality of hard corals turbid lagoon at Fanning Island (Central Pacific) had occurred, but an increased number of colonies exhibited an abundance of primarily branching corals although symptoms of stress such as parhal bleaching and exces- the coral community was less diverse than in a clear sive mucus secretion. Marszalek (1981) suggested that lagoon with mostly massive and encrusting corals (Roy prolonged turbidity was more detrimental than short- & Smith 1971, Maragos 1974). term accumulation of sediments. Dredging for 10 mo (October 1986 to July 1987) caused heavy sedimentation on an intertidal reef in Historical records of sedimentation on coral reefs Thailand and decreased both living coral cover and species diversity (B. E. Brown unpubl.). More diverse Coral skeletons contain a historical record of areas \nth more susceptible coral species have been sedimentation events because they trap terrigenous slower to recover. Rapid growth of injured colonies has sediments (Cortes & hsk 1984, Isdale 1984). Fluores- led to rapid recovery with respect to living coral cover, cent bands of fulvic acids within the yearly growth although the number of coral species has not reached bands are indicators of runoff, and large corals can pre-dredging values. provide a long record of runoff events (Isdale 1984). Rogers: Responses of cor a1 reefs to sedimentation 189

With pollen analysis and of sedi- to sedimentation levels is a result of assumptions that ments, it is possible to learn more about the processes certain levels are 'high' and others 'low' (see below, of sedimentation which influence coral reef develop- 'Thresholds'). Also, use of different methods, particu- ment. Nichols & Brush (1988) assessed relative in- larly sediment traps of different types, has complicated fluences of human activities on natural sedimentation interpretation and comparison of results from different rates in a swamp near Reef on St. John, sites. For example, traps with high height to aperture USVI. Extensive deforestation in the 18th and 19th ratios will be less subject to resuspension of their con- centuries on sugar cane plantations in the Reef Bay tents than shallower traps. Traps placed on or just watershed apparently resulted in no dramatic changes above the substrate collect more sediments than those in sedimentation rates. Presumably, in this case, near- higher in the (Ott 1975). Mean sedimen- coral reefs would not have suffered deleterious tation rates for reefs which are not subject to stresses effects from increased sedimentation as a result of from human activities range from less than 1 to about clearing of the hillsides. In a study of Reef, Fish and 10 mg cmp2 dC1 ( 1). In the absence of better Hawksnest Bays, St. John, Hubbard et al. (1987) found information, we can suggest that chronic rates of grea- a gradual reduction in coral growth over the last 100 to ter than 10 mg cm-' d-' are 'high' (see also Pastorok & 200 yr (based on limited data from coral heads). In Bilyard 1985). Confusion also arises over differential some cases, the growth decline corresponded to the responses to reduced light from turbidity and smother- period following intensive cultivation of the island. ing by sediment particles. They suggest that recovery of the forests may have In reef zones with heavy sedimentation (whether been accompanied by a decrease in the ability of the from natural processes or human activities), one might land to hold and retain sediment and water as more hypothesize the following, relative to areas with less extensive vegetation (e.g. grasses) was shaded out by sedimentation: (1) lower species diversity, with some trees. Breakdown of the terracing systems from the species absent; (2) less live coral (percent cover); (3) plantation era could also lead to an increase in near- greater abundance of forms and species with greater shore siltation. When trylng to analyze the effects of resistance to sediment smothering or reduced light hstorical and current land-clearing practices, it should levels; (4) generally smaller coral colonies, because of be remembered that modem practices of clearing land their greater efficiency at rejecting sediments; or, (5) with bulldozers that can remove topsoil down to under- generally larger colonies, because sediments limit lying and completely uproot trees are poten- recruitment; (6) lower growth rates; (7) an upward shift tially far more destructive than past methods. in depth zonation; (8) a greater abundance of branch- ing forms. Average size of coral colonies on a particular reef may Relation of sedimentation to coral and coral reef give little indication of the influence of sedimentation. distribution On Cahuita Reef, Costa hca, Cortes & &sk (1984)found a correlation of heavy river discharge with lower diver- Sedimentation is a major controlling factor in the sity, lower cover, lower growth rates, and generally distribution of reef organisms and in overall reef larger coral colonies. Maragos (1974) also found larger development (Hubbard 1986, Macintyre 1988). For colonies in the turbid lagoon than in the clear lagoon at example, reefs are generally better-developed, have Fanning Island. Brown et al. (1986) speculate that fusion more coral species, higher coral cover, and faster rates of Goniastrea colonies into larger colonies in shallow of framework accretion the farther they are from sour- areas off Thailand could be a response to hlgher ces of runoff or the lower the sediment load in overlying sedimentation rates. In contrast, smaller colonies were waters (Randall & Birkeland 1978, Morelock et al. 1983, associated with high sedimentation rates in Puerto Rico Hubbard et al. 1987). However, because of the com- (Loya 1976) and Bermuda (Dodge & Vaisnys 1977). plexity of reefs and the numerous factors which affect Live coral cover and species diversity is much lower growth and survival of corals, it is not necessarily valid on the inner east wall of Salt River to compare 2 areas and conclude that observed differ- on St. Croix (USVI), than on the inner west wall where ences in coral community composition are due to differ- sedimentation rates are much lower (Hubbard 1986). ent sedimentation rates. Documentation of a correla- However, these 2 parameters are similar on the more tion of high sedimentation levels with a particular seaward, outer portions of the walls where rates of assemblage of coral species is not the same as demon- sedimentation are comparable (Rogers et al. 1984). strating a causal relationship between this parameter At Cahuita Reef, Costa Rica, characterized by heavy and coral dstribution patterns. sedimentation rates (Table l), the abundant corals Some of the confusion which arises when interpret- were agaricites, Siderastrea radians, and ing the composition of a coral comn~unityas a response porites (Cortes & Risk 1984). Loya (1976) 190 Mar Ecol. Prog. Ser. 62: 185-202, 1990

Table 1. Comparison of sedimentation rates and turbidity levels for different reefs

I Location Rates Total suspended Comments Source (mg cm-' d-') solids (mg I-')

Caribbean Jamaica (Discovery Bay) 0.5- 1.1 Reef lagoon, Dodge et a1 (1974) (means for traps 50 cm ca (4 m deep) above substrate) St Thomas, USVI 0.8 +_ 0.4 -5.8 ? 13.3 Five coral reef areas, Rogers (1982) (means 2 SE for traps 3-5 m deep 10 cm above the substrate) 0.1 f 0.1- 1.6 k 0.7 (means f SE for traps 50 cm above the sub- strate) Puerto Rico 1 - 15 Reef 9-33 m deep Cintron et al. (1974) Puerto Rco 2.5 f 0.9 - 2.6 i. 1.2 Backreef 4 m deep Rogers (1983) (means f SE for traps 50 cm above the sub- strate) 9.6 -C 2.4 (means f SE for traps 10 cm above the sub- strate) Costa Rca (Cahuita) 30-360 Cortes & Risk (1984) 40 Tomascik & Sander (1985) Barbados ca5 to 10 Barrier reef 13.5-45 m Ott (1975) (means for traps ca 5 cm above the sub- strate - 7 stations) 1 (means for traps ca 1 m above the substrate - l station) --Pacific Hawaii (Kaneohe Bay) Rates from lagoon Maragos (1972) slopes, stabons 6 m deep or less; reefs subjected to several stresses, including heavier than normal runoff during study

reported higher cover by , &ion- In a study of the diskibution of coral communities tastrea cavernosa, Siderastrea radians, and Diplona located near 2 rivers in , Randall & Birkeland strigosa, fewer coral species, and less overall live cover (1978) concluded that observed decreases in natural on a reef receiving up to 15 mg cm-* d-' than on a sedimentation rates along a gradient from the river nearby reef with less sedimentation. mouths to the open sea explained the increase in In 1983, Morelock et al. (1983) reported that Algar- number of coral species, from less than 10 to over 100, rob0 reef and Escollo Rodriguez reef off the west coast and number of genera, from less than 10 to 35 and of Puerto Rico were being buried by silt. At Algarrobo, above. Percent living coral cover increased from less only Porites astreoides, Montastrea cavernosa, and Mil- than 2 to over 12 along the same gradient. The authors lepora alcicornis were present, and live coral cover was predicted that sed~mentationrates ranglng from 162 to less than 2 %. Heavy sedimentation at these reefs was 216 mg cm-' d-' will be associated with less than 10 attributed to increased discharge from rivers and ero- species while rates from 5 to 32 will be correlated with sion resulting from agriculture and development. over 100 coral species (data converted from original). Rogers: Responses of :oral reefs to sedimentation 191

Because of the variety of environmental factors which SEDIMENTATION EFFECTS AT THE can affect coral growth and distribution, caution should ORGANISM LEVEL be used in interpreting observed distnbution patterns as responses to single factors such as sedimentation Although burial of corals generally leads to death and in extrapolating findings to other locations. after a number of hours (Mayer 1918, Marshall & Orr The importance of bottom topography in determin- 1931), some species can withstand applications of large ing coral distribution should not be underestimated. amounts of sediments in the laboratory (Edmondson Highest coral diversity is often associated with forereef 1929, Hubbard & Pocock 1972, Bak & Elgershuizen slopes (Porter 1972, Sheppard 1982), presumably at 1976, Lasker 1980) and in the field (Edmondson 1929, least partly because sediments do not accumulate as Marshal1 & Orr 1931, Lasker 1980, Rogers 1983). Corals easily in these areas. Around the island of St. John, haie a variety of mechanisms for coping with sedi- numerous fringing reefs exhibit relatively high coral ments including use of their tentacles and cilia, sto- cover where they slope steeply to about 10 m to end modeal distension through uptake of water, and entan- abruptly on a flat sandy or algal plain. However, in a glement of particles in mucus which later sloughs off few locations where deeper water is close to shore and the colony surface (Hubbard & Pocock 1972). Corals a sloping bottom exists, vigorous coral growth is found exhibit both active and passive removal of sediment to at least 30 m (C. Rogers pers. obs.). particles (Lasker 1980). Where currents are strong, Adey et al. (1977) provided an interesting geological water movement will help to keep sediment particles perspective on development of western Atlantic reefs from settling on colony surfaces, and corals will have to and further evidence of the way sedimentation con- spend less energy in sediment rejection. trols reef growth. They suggested that high turbidity Species differ in their ability to reject sediments, with and nutrient levels, which resulted from erosion of colony and calyx morphology playing an important role Pleistocene shelves, caused deterioration of shallow (Hubbard & Pocock 1972). Colonies of Agaricia Acropora paln~ata reefs over 7000 yr ago. As water agaricites and Montastrea annularis exhibit changes in quality improved, coral species better adapted to the orientation and morphology which appear to reflect deeper water established communities on these relict adaptations to sediment stress (Bak & Elgershuizen reefs. Hubbard et al. (1986) noted a dramatic change 1976). Logan (1988) suggests that the frequently in the style and rate of reef accretion along the mar- observed orientation of the large calyx in Scolymia gins of Salt fiver submarine canyon, St. Croix, related cubensis at a steep angle from the horizontal may be an to formation of the Salt River 5000 to 6000 yr adaptation whlch facilitates sediment removal. ago. Subsequently, accretion has slowed substantially Field observations are sometimes contradictory and in response to increased levels of suspended sedi- at times appear to differ from laboratory results. For ments. example, laboratory experiments (Hubbard & Pocock 1972, Bak & Elgershuizen 1976) indicated that Porites astreoides would be inefficient or only moderately Recruitment good at rejecting sediments, relative to other species, but Morelock et al. (1983) and Cortes & fisk (1984) Sedimentation is one of several parameters which found it one of the most abundant species in heavily affect coral recruitment (Birkeland 1977, Bak & Engel sedimented areas. In contrast, Bak (1978) documented 1979, Birkeland et al. 1981, Rogers et al. 1984). Coral susceptibihty of this species to dredging. Meandrina larvae tend to settle on vertlcal surfaces possibly in meandrites rejected sediments very efficiently in Bak & response to higher sedimentation rates, as well as com- Elgershuizen's (1976) laboratory experiments, but were petition with algae, and other factors (Birkeland 1977, incapable of rejecting any sediments in Hubbard & Rogers et al. 1984). Coral larvae cannot successfully Pocock's (1972) studies. Additional studies in the field establish themselves in shifting sediments. Increases in and laboratory using standardized methods with close sediment input (either in suspension or as accumulat- attention to growth habitat might resolve some of the ing particles) could radically alter the distributions of apparent discrepancies. reef organisms by influencing the ability of their larvae In a study of San Cristobal reef, Puerto &CO,Rogers to settle and survive. Tomascik & Sander (1987) sug- (1983) found that sediment particles could not adhere gest that lower light levels may inhibit development of to the cylindrical branches of Acropora cervicornis but coral larvae by reducing the amount of energy avail- were able to accumulate on flat portions of Acropora able to maturing ova or embryos. They found reduced palmata. sediments were applied in situ to numbers of larvae from colonies of Porites porites colonies of Montastrea annularis, Diploria striyosa, D. growing on reefs polluted by nutrients and suspended clivosa, A. paln~ata, and A. cervicornis in different particulate matter. frequencies and doses. A. palmata was the most sensi- Table 2. Coral responses to sediment application in the field and laboratory

Coral species Treatment Amount or Duration Response/effect Source

- - -= Field studies Monlastrea annularis Field application 1000 to 1 dilution Death of colonies Thompson & Bright (1980) of dri.lling mud Agaricia agariciles Death of colonies Acropora cervicornls Death of colorues Poriles aslreoides No mortality Porrles d~varrcata No mortality Porites furcata No mortality Dlchocoenia stokes1 No mortality Monlastrea cavernosa Reef sediment under natural Evldence of the ability to clear Lasker (1980) conditions m the field up to 345 mg sediment 25 cm-' d-' (overestimate) Ponles aslreoides Dredging Death of entire colony Bak (1978) or portion Madracis n~lrabills Decreased calcification (33 '10) Agarlcra agarrcites Decreased calcification (33 %) Montastrea annular~s Long-term resuspension Decreased growth Dodge et al. (1974) of bottom sediment Acropora palmata Field appl~cation Death of underly~ngtissue Rogers (1983) of reef carbonate sand Montaslrea annularis 800 mg cm-' Death of underlying 400 mg cm-' Temporary bleaching D~ploriaslrlgosa Daily apphcation of 200 mg cm-2 No effect Acropora cervrcornls Dally applrcahon of 200 rng cm-' No effect Montaslrea annular~s Dally appllcahon of 200 mg cm-' No effect Montastrea annularrs Peat ~njectec 525 mg I-' Decrease In net production; Dallmeyer et al. (1982) lnto resplrometer increase In Acropora palmata Reef sediments applied in Decrease in net production; Abdel-Salam & Porter Montaslrea annularis resplrometer increase in resplratlon (1988) Dlploria strrgosa Table 2 (continued)

Coral species Treatment Amount or concentration Duration Responseleffect Source

Laboratory studies 19 Caribbean species Lab applicat~onof carbonate 430 mg cm-'' Up to > 24 h A. palmala, A, cervicornis, Bak & Elgershuzen (1976) examined sand from the reef P. astreoides, & A, agaricites (horizontal onentation) least efficient; ColpophyUia natans, D. strigosa, M. rnirabilis, among the most efficient Lab application of sand and oil 430 mg cm-' Lethal to: A. agaricites, M. annularis, D. stokesi, & MycetophyUia aliciae Montastrea annularis Drilling muds 0 PPm None Szmant-Froelich et al. (1981) 1 None 10 Respiration and calcification lower than control (but not statistically significant) 100 Calcification rate decreased by 84 % Respiration rate decreased by 40 % production decreased by 26 '10 after 5 wk uptake decreased by 48 % Ammon~auptake decreased by 49 % Feedng response was impaired Corals were bleached and several died by the end of the experiment blontastrea cavernosa Lab application of 25 m1 of 1 part mud or calcium Mortality for all species Thompson & Bright Montaslrea annulan's drilling mud and pure carbonate and 1 part from drilling mud (1977) Diplon'a strigosa calcium carbonate Faster cleaning rate for D. sln'gosa (322 mm2 h-') than the other 2 species Converted from original data 194 Mar. Ecol. Prog. Ser. 62: 185-202, 1990

tive of the species tested. Single applications of 800 mg thiformis, and Diploria strigosa) and species with larger cmp2 to M. annularis colonies and 200 mg cmp2 to A. calices (e.g. M. cavernosa). In this experiment, corals palmata colonies caused death of underlying coral tis- did not have the usually concurrent problem of sedi- sue, while the other experimental species were not ment removal. significantly affected by any of the doses. The differ- Synthesis of field and laboratory observations ential response of A. cervicornis and A. palmata to (Table 2) suggests the following: (1) Different species sediment application implies we cannot assume that have different capabilities of clearing themselves of branching corals are generally more tolerant than head sediments or surviving lower light levels. (2) The corals to sediment stress although for some species this amount and type of sediment will influence the ability appears to be the case (Chappell 1980). Response will of a coral to reject sediments which settle on the colony probably differ depending on whether the stress is from surfaces. (3) Sediment rejection is a function of mor- reduced light levels from high turbidity or from phology (of the whole colony, the calices, and the accumulating particles. For example, A. cervicornis colony surface), orientation (vertical, horizontal), and was the most susceptible species to shading in Rogers' behavior. (4)Experimental corals may not respond nor- (1979) experiment. mally in the laboratory. Dredging near a in Curaqao resulted in mortality of portions or entire colonies of Porites astreoides (at depths of 15 to 25 m) and decreased Changes in coral growth with increases in calcification rates for Madracis mirabilis and Agaricia sedimentation agancites, with calcification remaining suppressed for over 1 mo after the turbid water cleared up (Bak 1978). The growth of a coral skeleton is the end result of The apparent cause was reduction of light levels to only several physiological processes which can be altered 1 % of surface illumination. by environmental conditions. It is not always clear what Although we might expect smaller-polyped 'auto- triggers specific growth responses in corals. Coral trophic' corals which depend more on light to succumb growth does not appear to be a simple indicator of more quickly to turbid conditions than large-polyped excessive sedimentation. Skeletal growth is a function corals which rely more on as an energy of linear extension, bulk density, and calcification, source, we lack data either to conclusively support the parameters which can vary independently (Barnes & validity of separating corals into 'autotrophic' and 'het- Crossland 1980, Gladfelter 1982, 1983, Dodge & Brass erotrophic' categories (Porter 1976) or to test the 1984). Growth can vary greatly between colonies of the hypothesis of differential sensitivity. Montastrea caver- same species under similar environmental conditions nosa (with large calices), and Siderastrea siderea and and even within a single colony (Rogers 1979, Brown & the Pacific coral Porites lutea (both with small calices), Howard 1985). This variability makes rigorous statisti- are relatively tolerant of high levels of sedimentation cal analysis and interpretation of results difficult. (Lasker 1980, Maragos pers. comm.). Dodge (1982) exposed Montastrea annularis colonies to There are few data on the susceptibilities of different drilling fluid and found decreases in the length of the coral species to suspended sediments. Maragos septa, columella, endothecal base, and fossa. However, (unpubl.) indicates that several Pacific species, includ- Foster (1980) did not find a simple relationship be- ing many with large polyps, are less sensitive than tween fossa length and sedimentation levels. other species and suggests that corals normally found Because corals and associated zooxanthellae depend in shallow near shore areas will be more resistant than on light for rapid of calcium carbonate those on seaward reefs. Examination of a table pre- (Chalker 1981), high turbidity can reduce coral growth sented in Randall & Birkeland (1978) suggests that the rates. Growth may also decrease because of - following Pacific corals are relatively resistant to high sion of energy to removal of sediment particles. Dodge sedimentation, based on their occurrence in areas et al. (1974) described the inverse correlation between where the highest sedimentation rates were recorded: natural sedimentation and Montastrea annu1an.s Pocillopora darnicornis, verilli, Porites lutea. growth rates. Growth rates of this species from the East Brown (unpubl.) found that P. lutea was less suscept- Flower Gardens Bank reef in the of Mexico were ible to the effects of dredging at a site in Thailand than negatively correlated with discharge of sediments and some of the faviid species. fresh-water from the Atchafalaya River (Dodge & Lang In a simulation of extreme turbidity, the shading of a 1983). section of a coral reef off Puerto Rico, Rogers (1979) Hubbard et al. (1987) documented a correlation found that Acropora cervicornis colonies were the most between short-term decreases in Montastrea annularis sensitive, followed roughly by species with medium- growth and construction in the watershed of Hawksnest sized calices (Montastrea annularis, Diploria labyrin- Bay, St. John. Hubbard & Scaturo (1985) found that Rogers. Responses of col:al reefs to sedimentation 195

growth rates of 7 coral species from Cane Bay and Salt Some corals may fuse in response to increased fiver, St. Croix (USVI), decreased with depth and sug- sedimentation (Brown et al. 1986). Hughes & Jackson gested that turbidity and sedimentation were among the (1985) reported higher survival rates for colonies which major controls of growth rate. Colonies of M. annularis fused than for those which arose from fission of larger grew faster at Cane Bay than at corresponding depths at colonies in reefs off Jamaica. Salt hver where concentrations of suspended materials are consistently higher. Examination of growth bands suggested slower growth of Diplorja colonies in Ber- Changes in coral metabolism with increases in muda for several years prior to death from siltation sedimentation associated with dredging (Dodge & Vaisnys 1977). Tomascik & Sander (1985) investigated the effects of Particles in suspension in the water can alter both water quality on h4ontastrea annularis growth rates off intensity and spectral quality of light reaching reef Barbados over a gradient of increasing organisms, thereby affecting their metabolism. Few (primary , industrial effluent). They found that studies of coral metabolic responses to sediment stress mean concentration of suspended particulate matter have been conducted. Rogers (1979) shaded a portion (mg I-') was the strongest single estimator of growth of San Cristobal reef (Puerto Rico) to simulate the rates, with the most rapid coral growth occurring at the shading effects of turbidity and found decreased net site farthest from the primary pollution source. productivity by the coral community. Edmunds & Sometimes, some of the corals in an area die from Davies (1986, 1989) calculated energy budgets for sedimentation, although surviving colonies show no Porites porites colonies growing at 2 sites off Jamaica. decline in growth. Hudson et al. (1982) noted little Colonies growing at the site with lower light levels and suppression of growth in Porites lutea colonies from an higher sedimentation rates had lower growth rates but area around an oil drilling site although they attributed higher productivity because of photoadaptation. It a 70 to 90 % reduction in colonies of several species to would be interesting to determine energy budgets for smothering by drill cuttings. Brown et al. (unpubl.) P. porites colonies growing in areas with much higher noted that increased sedimentation on a coral reef in sedimentation rates than those reported in this study. Thailand led to death of 30 % of the P. lutea colonies Using a respirometer, Dallmeyer et al. (1982) found a but no evidence of decreases in linear growth of decrease in net production by Montastrea annularis remaining colonies of this species. colonies exposed to particulate peat during daytime experiments. At night, colonies exhibited increased respiration and active clearing behavior. Colonies of Changes in coral growth form with increases in Acropora palmata, Montastrea annularis, and Diploria sedimentation strigosa showed significant increases in respiration and decreases in net photosynthesis following application Sedimentation can affect not only growth rates but of sediments from a road construction site in other also colony morphology. Foster (1979, 1980) has shown respirometer studies off St John, USVI (Porter & Rogers that Montastrea annulan's colonies exhibit changes in unpubl.). These species responded in similar ways to their skeletal morphology when transplanted to loca- doses of carbonate reef sediments in experiments off St tions with higher sedimentation rates. Hubbard et al. Croix, USVI (Abdel-Salam & Porter 1988). The terri- (1987) suggest the multi-lobed, knobby growth form of genous sediments had more pronounced effects on this species may reflect sediment stress. In studies off both respiration and photosynthesis. The integrated St. John, they found this form consistently grew closer P/R ratios for all sediment-treated corals in the St Croix to sources of runoff and was common in backreef areas. study were < 1. Barnes (1973) speculated that the sides of a colony could approach a critical radius because they receive less light than the upper colony surface. A columnar Effects of drilling fluids on coral reef organisms growth form could result, with this column later divid- ing into units of smaller radius. This process of column The search for additional supplies of oil and natural formation and isolation could be accelerated by sedi- gas has led to a dramatic increase in offshore drilling ment particles settling in concave areas of the colony and concern over the possibly detrimental effects of surface and killing the underlying tissues. The flat- discharged drilling fluids (used to remove drill cuttings tened or plate-like growth form of M. annularis which and to lubricate drill bits). In their comprehensive appears to be an adaptation to low light intensities review of the effects of these fluids on reef corals, (Dustan 1975) would be less efficient at removing sedi- Dodge & Szmant-Froelich (1985) note that there is 'no ments than a more rounded form. clear-cut separation between effects due to sedimenta- 196 mar.Ecol. Prog. Se

tion alone versus those caused by potentially toxic organisms bore into and weaken the substrate (Hedley chemical constituents, or due to a synergism between 1925, Sano et al. 1987). With a decline in the number the two'. of crevices and hiding places that the reef provides, Exposure of corals (Montastrea annularis and other there is a reduction in both the number of individuals species) to drilling fluids can cause death (Thompson of fish and the number of species that the reef can 1979, 1980), alter feeding behavior (Szmant-Froelich et sustain. This decrease in both the number of fish and al. 1981), disrupt the normal pattern of expansion the number of species could be a function of a reduc- and retraction (Thompson & Bright 1980),alter physiol- tion in the amount of living coral cover as well as a ogy (Krone & Biggs 1980), cause morphological chan- decrease in the amount of shelter the reef can provide ges (Foster 1979, 1980) and lower the density of zoo- (Bell & Galzin 1984). Sano et al. (1987) found more xanthellae (Szmant-Froelich et al. 1981). Calcification species and individuals of fish on a living (mostly appears to be one of the first processes disrupted by Acropora spp.) reef than on a primarily dead reef exposure to drilling fluid (Szmant-Froelich et al. 1981). which had low structural relief following an Acanthas- In many of the experiments cited above, a drilling fluid ter planci infestation. Apparently, there was a further concentration of 0.100 m1 1-' appeared to be critical decline in fish abundance and diversity as the dead with lower concentrations eliciting little or no response. reef collapsed into rubble 2 yr later. Maragos (pers. Hudson et al. (1982) attributed a 70 to 90 O/O reduction in comm.) notes that fishermen in Kosrae reported their coral cover of several species in the to catch dropped by half following burial of some reefs drilling several years previous to their study. Dodge & and seagrass beds. Szmant-Froelich (1985) conclude that sensitivity to Dredging apparently can lead to a decrease in fish drilling fluid may vary widely among species, within diversity, but data are limited. Galzin (1981) reported species, and with the type and amount of fluid tested. that resumption of dredging in Grand Cul de Sac Marin, (), led to the disap- pearance of 20 fish species out of a total of 29 which RELATION OF SEDIMENTATION TO CORAL were observed (during a single census) after dredging REEF FISHES had ceased for over a . Fewer fish species were associated with areas near dredge sites. A loss in liv- Sedimentation can alter the complex interactions ing coral cover rather than a loss of topographical between fish and their reef habitat. Fish graze on dead relief may have been responsible for the suspected coral, breaking down the calcium carbonate skeleton decline. and producing large quantities of sediment; provide Amesbury (1981) found that the number of fish nutrients in their wastes; and graze on coral larvae, species decreased significantly at monitoring stations thereby influencing the reef's structure. Randall (1974) near a runway construction site in Truk where fine suggested that the continuous rain of sediments from sediments had accumulated from dredging and filling and surgeonfishes adversely affects reef activities. Burial of one coral mound resulted in disap- organisms. However, fish faeces may enhance coral pearance of all the fish, while partial burial of another growth (Meyer et al. 1983) and supply essential nu- patch reef led to decline of 50% of the species. He trients (Szmant-Froelich et al. 1981). In a synthesis of noted that territorial fish species and those with limited studies of the effects of fish on coral reef ranges remained even under conditions of high turbid- structure, Hixon (1986) noted that which ity and suggested that fish behavior was not a very defend algal territories directly influence coral recruit- effective indicator of environmental degradation. At ment and growth, as well as . Numerous (Central Pacific), the disappearance of studies demonstrate the effects of f~shgrazing on reef 12 species of Chaetodontidae () which algae (e.g. Ogden & Lobe1 1978). Economically impor- eat coral was correlated with extensive death of the tant fish (e.g. snappers, grunts) and conchs feed on corals from siltation associated with dredging (Houri- the benth~c microalgae and invertebrates in reef gan et al. in press). sediments. Herrnkind et al. (1988) studied the effects of siltation The highest number of fish species and greatest on () recruitment in the abundance of individuals tend to be associated with Florida Keys, USA. Following a series of laboratory forereef zones or other areas which provide the great- experiments and field surveys, they concluded that the est topographical relief and structural complexity (e.g. relative lack of juvenile lobsters in heavily silted areas Risk 1972, Luckhurst & Luckhurst 1978, Gladfelter et was a result of both lower postlarval settlement and al. 1980, Boulon 1987). The death of major reef-build- actual avoidance of algal habitats w~thhigh silt loads. ing corals, from sedimentation, disease, or other cau- Clumps of the red alga Laurencia spp. are preferred ses, can lead to collapse of the reef framework itself as hab~tatfor newly settled postlarval lobsters. Fewer prey Rogers: Responses of coral reefs to sed~mentation 197

items (e.g. gastropods and amphipods) are found in RECOMMENDATIONS FOR MONITORING algal clumps with large amounts of trapped silt. Silt SEDIMENT STRESS apparently did not have an effect on survival of pueruli through metamorphosis to the first benthic stage or on Peters & Pilson (1985) provide a list of methods for time to metamorphosis. Herrnkind et al. (1988) note monitoring coral stress responses which includes vis- that most of the silt in their survey areas was calcare- ual, physiological, and histopathological examination ous, probably resulting from biological sediment pro- (Table 3). Their study of the response of Astrangia cessing. However, they suggest that human activities danae to sediments is one of the few to date which which introduce siltation into marine waters or acceler- incorporates histological examination. ate normal siltation rates are detrimental to spiny lob- One useful and inexpensive monitoring technique is ster recruitment. the successive observation and photography of indi- vidual coral colonies over time to reveal sediment smothering, algal overgrowth, disease or bleaching. RECOVERY AFTER SEDIMENT STRESS Colonies should be selected randomly and identified with numbered plastic tags using plastic cable ties to Few examples of recovery of coral reefs after severe secure them to the substrate near the coral or to con- sediment damage have been documented. With respect crete nails driven into the substrate. Corals have to recovery and recolonization of reefs, Brown & Howard annual growth bands and patterns of growth which can (1985) suggest that 'both generalizations and predic- sometimes be correlated with changes in water quality tions are dangerous'. They recommend consideration of or other environmental disturbances (Dodge et al. each case individually. Sometimes increased sedimen- 1974, Hudson 1981). However, the colonies which are tation is accompanied by other stresses, prolonging or analyzed are the survivors and therefore possibly poor inhibiting recovery. Maragos (1972) estimated that 80 O/O indicators of stress. Further calibration of growth with of the coral communities in the lagoon in Kaneohe Bay, different conditions will make 'sclerochronology' even Hawaii, died because of a combination of dredging, more useful. Successful establishment and growth of increased sedimentation, and sewage discharge (see coral recruits presumably indicates sedimentation rates also Roy 1970). Six years after discharge of sewage into are not at a detrimental level. Kaneohe Bay ceased, dramatic recovery of corals and a No simple relationship exists anlong water transpar- decrease in the growth of the smothering alga Dictyo- ency (% Light transmission, Secchi disk depths), sphaeria cavernosa were reported (Maragos et al. 1985). nephelometer turbidity units, suspended matter con- Maragos et al. (1985) suggest that the sewage had centrations, and sediment deposition rates (Jerlov delayed or prevented recolonization of corals on 1970). When feasible, all of these should be measured. dredged surfaces by stimulating growth of algae which When resources are limited, water samples can be competed with corals for space. filtered for calculations of suspended matter concen-

Table 3. Methods for monitoring coral responses to sedimentation (adapted from Peters & Pilson 1985)

Visual observations (behaviour and appearance) 1. Unusual polyp contraction or expansion 2. Extrusion of mesenterial filaments 3. Unusual mouth opening responses 4. Change in feeding behaviour 5. Increased mucus production/muco-ciliary activity 6. Decrease in zooxanthellae concentration ('bleaching') 7. Appearance of bare skeleton or abnormal tissue growth (e.g. lesions) 8. Appearance of accumulations of layers of sediments over living portions of colony Physiological measurements 1. Variation in metabolic rate based on respiration 2. Change in excretion rate/excretory products 3. Differences in biochemical composition 4. Decrease on increase in calcification rates (growth rates) 5. Change in photosynthesis by zooxanthellae Histopathological examinations 1. Reduced gonad development or change in reproduction cycle 2. Change in morphology and/or composition of tissues and cells, abnormal accumulations of bioyenic deposits 3. Presence of microparasites or pathogens 198 Mar Ecol. Prog. Ser. 62: 185-202, 1990

trations. The quantity and quality of light reaching degradation of water quality with continued logging, photosynthetic reef organisms should be measured Hodgson & Dixon (1988) concluded that the predicted when possible. increase in revenue from logging was less than the loss in income to and fisheries resulting from degra- dation of the marine systems. PREDICTING THE EFFECTS OF COASTAL DEVELOPMENT ON CORAL REEFS FUTURE RESEARCH NEEDS Dredging is not likely to cease especially in small developing tropical islands and countries where other More rigorous, comprehensive research is needed to sources of building materials are inaccessible. Hillsides quantify the response of individual reef organisms and will continue to be cleared of vegetation to make way the reef system as a whole to sedimentation from for more and more shoreline development. Conse- dredging and watershed development (runoff). Ideally, quently, we must find the most effective ways to pre- scientists should conduct a multidisciplinary study to dict and to limit the consequences. Often the careful augment our understandmg of how increases in planning and implementation of protective measures sedimentation alter the structure and function of coral during construction projects can reduce damage to reefs and associated marine ecosystems. Emphasis marine systems (DuBois & Towle 1985, White 1987). should be on changes in abundance and spatial For example, use of silt screens, settling , and arrangement of dominant benthic organisms. If scien- berms can reduce adverse effects (Salvat 1987, White tists are going to effectively assess changes and trends 1987, Maragos 1989).Natural drainage patterns should on coral reefs, they must start using standardized be altered as little as possible. Developers should be monitoring methods. Long-term data sets are abso- required to monitor the effects of coastal construction lutely necessary for these complex ecosystems. on nearby marine ecosystems as a condition of their The interactions and linkages among mangroves, permits. seagrass beds, and coral reefs require further study, In some cases, scientists are hindered in their evalua- along with the effects of sedimentation on these interac- tion of the consequences of a particular coastal project tions. More studies on the life cycles of fishes and their because of a lack of information on basic coral biology dependence on the major ecosystems are a prerequisite and the lack of even simple models to aid in prediction for effective . We need to know of environmental responses. Necessarily vague scien- more about how fish and shellfish depend on and tific assessments of possible impacts (e.g. from hotel influence their habitats at different stages of their life construction on a beach with an offshore reef) are easy cycles. We need to discover how pollution, sedimenta- to ignore in the face of more definitive, concrete tion from runoff and dredging, and other stresses from economic benefits. human activities affect (directly and indirectly) the It is essential to incorporate environmental consider- organisms, the food webs, the habitats and the interac- ations into coastal zone management decisions. Hodg- tions among them. Exactly what is the connection son & Dixon (1988) provide an interesting evaluation of between habitat degradation and fisheries decline? alternative plans for the development of the area of Bacuit Bay, (Philippines) where nature-based tourism (primarily ) and marine fisheries Thresholds are in conflict with the logging industry. Clearing of trees and building of logging roads have increased Further research is needed on the threshold levels for sheet erosion and introduced high levels of sediment individual reef species (hard corals, soft corals and into the bay. Hodgson & Dixon (1988) found that high others) and for the reef ecosystem as a whole - the levels rates of sediment deposition significantly reduced coral above which sedimentation has lethal effects for par- cover and diversity, with a reef closest to the mouth of a ticular species and above which normal functioning of river which empties into the bay losing almost half its the reef ceases. With reference to experiments on indi- live coral following heavy rainfall. Based on a 1 yr vidual organisms, we need more studies on corals other study, these authors predict an annual decrease in than Montastrea annularis. What turbidity level (con- coral cover of 1 % for every additional 400 mt kmp2 of centration of total suspended solids) will result in a sediment deposition in Bacuit Bay; an annual loss of given percent decrease in the amount of living coral one coral species per increase of 100 mt km-' sediment cover? What sedimentation levels cause death of coral deposition; and a decrease of 2.4 1L in fish for species in the field? 'Normal' sedimentation rates for each 1 O/O decrease in coral cover Using a model based coral reefs appear to be on the of 10 mg cm-2 d-' or on these results and various assumptions, e.g. about less, and typical suspended solids concentrations less Rogers: Responses of coral reefs to sedimentation 199

than 10 mg 1-' (Table l), but how high can these respect to late Cenozoic coral reef development in the concentrations and rates go before reefs and reef organ- western Atlantic. Proc. 3rd int. Coral Reef Symp. 2: 15-21 isms are adversely affected? Do responses to terrigenous Amesbury, S. S. (1981). Effects of turbidity on shallow water reef fish assen~blages i.n Truk, Eastern . sediments differ from responses to calcium carbonate Proc. 4th int. Coral Reef Congr. 6: 491496 sedln~ents?There is a need to study the effects of both Amesbury, S. S., Clayshutte, R. N.. Determan, T A., Hedlund, reef-derived and anthropogenic sediments on different S. E.. Eads, J. R. (1978). study of coral species and different reef organisms under as airport runway expansion site, Moen, Truk. Eastern Caroline Islands, Part A: Baseline study. Univ. of Guam realistic conditions as possible. We need more field Mar. Lab. Tech. Rep. No.51, p. 1-87 stud~eson responses of organisms to sediments during Bak, R. P. M. (1978). Lethal and sublethal effects of dredging dredging and to application of sediments actually col- on reef corals. Mar. Pollut. Bull. 9: 14-16 lected from construction and dredging sites. Bak, R. P. M,, Elgershuizen, J. H. B. W. (1976). Patterns of oil Are short-term, acute pulses of sediments into the sediment rejection in corals. Mar. Biol. 37: 715-730 Bak, R. P. M,, Engel, M. S. (1979). Distribution, abundance, reef environment less detrimental than chronic sedi- and survival of juvenile hermatypic corals () mentation at lower levels? At what concentration of and the importance of life history strategies in parent coral suspended sediments does coral growth cease? Does comn~unity.Mar. Blol. 54: 341-352 coral reef zonation shift to shallower depths with high Banner, A. H. (1968). A freshwater 'kill'on the coral reefs of Hawaii. Hawaii Inst. Mar. Biol. Tech. Rep. No. 15, p. 1-29 turbidity? Only with greater understanding of coral Barnes. D. J. (1973). Growth in colonial scleractinians. Bull. physiology can we begin to differentiate the effects of mar. Sci. 23: 280-298 disturbance, whether natural or man-made, from nor- Barnes. D. J., Crossland, C. J. (1982). Variab~tyin the calcifi- mal long-term fluctuations on reefs (Brown & Howard cation rate of measured wth 1985). What are the cun~ulativeeffects of a number of radioisotopes. Coral Reefs l: 53-57 Bell, J D., Galzin, R. (1984). Influence of live coral cover on small development projects, and how do they compare communities. Mar. Ecol. Prog. Ser. 15: to the effects from a single large project? We need 265-274 answers to all of these questions to enable us to predict Berwick, N. L.. Chamberlin, R. (1985). Systems analysis for the consequences of coastal development projects. integrating tropical coastal resources with watershed use. Proc. 5th int. Coral Reef Congr. 5. 569-575 Computer models should be useful in this regard. Birkeland, C. 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This review was presented by Professor C. Birkeland, Guam, Manuscript first received: May 15, 1989 USA Revised version accepted: January 8, 1990