United States Office of Water September 1983
Environmental Protection Program Operations (WH-546) 430/9-83-010
Agency Washington DC 20460
<>EPA Ecological Impacts
of Sewage Discharges
on Coral Reef Communities
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ECOLOGICAL IMPACTS OF SEWAGE
DISCHARGES ON CORAL REEF COMMUNITIES
September, 1983
by
Tetra Tech, Inc.
1900 116th Ave., N.E.
Bellevue, WA 98004
Contract Number 68-01-5906
Prepared for:
Office of Water Program Operations
U.S. Environmental Protection Agency
Washington, D.C. 20460
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EPA REVIEW NOTICE
This report was prepared under the direction of the Office of Marine
Discharge Evaluation (WH-546), Office of Water Program Operations, Office of
Water, U.S. Environmental Protection Agency, 401 M Street, S.W., Washington,
D.C.,'20460, (202) 755-9231.
This report has been reviewed by the Office of Water and the Office of
Research and Development, U.S. Environmental Protection Agency, and approved
for publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
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ACKNOWLEDGEMENTS
The report was prepared under EPA Contract No. 68-01-5906. We wish to
thank the Office of Marine Discharge Evaluation of the U.S. EPA for
management and review of this project. Dr. Henry Lee and Mr. Mark Schaefer
of U.S. EPA provided a bibliography of pollution effects on coral reefs. We
are also grateful to Dr. Henry Lee for initial regression analyses of
sedimentation data. Many persons responded generously to our request for
information. We would like to thank all of them, especially Drs. P. Alpino,
C. Birkeland, D. Cheney, J. Gonzalez, C. Rogers, and E. Shinn.
Drs. C. Birkeland and S.V. Smith made valuable comments on the first draft.
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CONTENTS
Page
INTRODUCTION 1
CORAL REEF ECOLOGY 2
Coral Reef Architecture and Habitats 2
Biological Communities 4
Abiotic Controls on Coral Reef Development 10
SENSITIVITY TO POLLUTION 11
RECOVERY POTENTIAL 13
IMPACTS OF SEWAGE DISCHARGES 18
POTENTIAL IMPACTS 18
Oxygen Consumption 18
Nutrient Enrichment 18
Sedimentation 19
Toxicity 19
CASE HISTORIES 19
Gulf of Aqaba, Red Sea 22
Kaneohe Bay, Hawaii 23
IMPACTS OF SEDIMENTATION 34
POTENTIAL IMPACTS 34
Sensitivity of Corals to Sedimentation 34
Individual Effects 36
Population and Community Effects 39
CASE HISTORIES 39
Natural Sources of Turbidity/Sedimentation 41
Anthropogenic Sources of Turbidity/Sedimentation 45
SYNTHESIS • 50
NUTRIENT ENRICHMENT 51
11
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SEDIMENTATION 53
TOXICITY 61
CONCLUSION 67
APPENDIX: LITERATURE SEARCH AND INFORMATION SOURCES 69
REFERENCES 72
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FIGURES
Number Page
1 Generalized profile of a coral atoll 3
2 Idealized variation of coral growth forms, diversity, and
abiotic factors across a simple reef profile 12
3 Sewage loading in Kaneohe Bay and Kailua Bay, Hawaii, 1950-
1979 24
4 Location of coral reefs and prediversion/postdiversion
sampling stations, Kaneohe Bay, Hawaii 25
5 Spatial gradient and- parameter responses to sewage diversion,
Kaneohe Bay, Hawaii 31
6 Relationships between percent living coral cover, turbidity,
and water depth, Negro-Bank Reefs, Puerto Rico 43
7 Growth rate of coral (Montastrea annularis) in relation
to sediment resuspension rate, Discovery Bay, Jamaica 46
8 Coral cover versus sediment cover, Kaneohe Bay, Hawaii 48
9 Coral species richness as a function of sedimentation rate,
Guam 55
10 Coral percent cover as a function of sedimentation rate,
Guam 56
11 Coral colony size as a function of sedimentation rate,
Guam 57
12 Coral species richness as a function of coral cover, Guam 58
IV
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Various Levels of Sedimentation - Summary
TABLES
Number
1 Primary Framework Builders of Coral Reefs 6
2 Estimates of Coral Reef Recovery Time Following Disturbance 14
3 Case Histories of Sewage Discharge Impacts on Coral Reefs 20
4 Summary of Responses to Sewage Diversion, Kaneohe Bay,
Hawaii 3U
5 Sensitivity of Some Common Coral Species to Sedimentation 37
6 Case Histories of Sediment Impacts on Coral Reefs 40
7 Coral Community Structure and Sedimentation Rates in Fouha
and Ylig Bays, Guam 44
8 Estimated Degree of Impact on Coral Community Caused by
60
9 Estimated Degree of Impact on Coral Community Caused by
Various Levels of Sedimentation 62
10 Worst Case Estimates of Solids Deposition Rates for Sewage
Outfalls near Coral Reefs 63
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INTRODUCTION
Sewage pollution of coral reefs has been recognized as a major
environmental problem for some time (e.g., Doty 1969; Banner 1974). Current
U.S. environmental regulations allow Publicly Owned Treatment Works (POTWs)
to apply for a modified National Pollutant Discharge Elimination System
permit to discharge effluent receiving less-than-secondary treatment to
marine waters. Under Section 301(h) of the 1977 Clean Water Act (as amended
by the Municipal Wastewater Treatment Construction Grant Amendments of 1981,
P.L. 97-117), POTWs are required to demonstrate to the U.S. Environmental
Protection Agency that less-than-secondary treatment of their discharge will
not result in certain adverse ecological impacts. The effects of effluent
suspended solids and nutrients on coral reef communities are of special
concern. In the context of the 301 (h) sewage discharge evaluation program,
coral reefs are considered "distinctive habitats of limited distribution."
Their protection is especially important because of their ecological
significance or direct value to man.
This report provides a synthesis of current information on the
ecological impact of sewage discharges on coral reefs. Three major
components of sewage pollution are addressed: 1) eutrophication associated
with high nutrient concentrations in discharged wastewaters,
2) sedimentation of suspended solids, and 3) toxic effects. A review of
sewage discharge impacts is presented, with emphasis on nutrient enrichment
aspects (Section 2). The effects of solids deposition on corals are
considered in Section 3. Finally, the available data are synthesized to
develop functional relationships between discharge characteristics,
sedimentation rates, and reef community impacts (Section 4).
The remainder of this introduction provides a brief summary of coral
reef ecology, the susceptibility of reef communities to pollution impacts,
and the potential for ecosystem recovery.
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CORAL REEF ECOLOGY
Literature on the basic ecology of coral reefs is voluminous. Most of
this information is reviewed in detail by Wells (1957), Stoddart (1969a),
Sheppard (1982), and others. The intent of the following sections is to
present brief descriptions of coral reef habitats, biological communities,
and environmental controls of reef growth. The reader is referred to the
reviews cited above and the specific papers cited below for further
information on coral reef ecology.
Coral Reef Architecture and Habitats
Based on geomorphology and dominant biotic assemblages, complex
classification schemes have been developed for coral reef types (Stoddart
1969a; Ladd 1977) and habitat zones (e.g., Wells 1957; van den Hoek et al.,
1975; Sheppard 1980a). A simplified version of reef zonation includes the
following characteristic habitats (Figure 1):
• Sandy beach - borders the reef proper; with calcium
carbonate sediments, low diversity, no living corals
• Coral lagoon - several meters to greater than 50 m deep;
varies from high cover and diversity of living corals to few
scattered heads interspersed with sandy bottom and seagrass
beds
• Reef flat - intertidal or shallow subtidal; usually high
diversity and cover with branching, encrusting, and delicate
corals in Caribbean; planer rock surfaces covered with algae
and seagrass in Indo-Pacific
• Reef crest - supratidal to shallow subtidal; high wave
energy zone on windward reefs; upper portions encompass
algal ridge or coral rubble zone
t Reef front and terrace - subtidal zone with generally steep
slope, complex topography, and large sediment transport;
"groove and spur" zone; often high diversity and cover with
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SOURCE: Modified from Demond, 1957
Figure 1. Generalized profile of a coral atoll.
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massive staghorn, brain, and branching corals (many delicate
gorgonians in Caribbean); deeper terraces may have scattered
coral heads interspersed with deep sediments
• Seaward reef slope or deep fore reef - deep subtidal zone
mostly beyond the influence of surface waves and currents;
steep to nearly vertical slope; patches of coral rubble and
sand; lower diversity, with zooxanthellae-containing corals
and algae rare or absent at greater depths.
Depth ranges for the above habitats vary depending on exposure, reef type,
geographic region, and water quality. As an example, the reef front of a
typical coral reef extends from near the surface to 15 m (49 ft), the
submarine terrace is found at about 15-18 m (49-59 ft), and the seaward reef
slope occupies the 18-100 m (59-328 ft) depth zone (Stoddart 1969a; Goreau
et al., 1979).
Biological Communities
The biological communities of coral reefs have been described in detail
by many authors (e.g., see references in Jones and Endean 1973, 1976).
Glynn (1973) reviewed reef communities and biotic interactions for the
Western Atlantic region [also see Milliman (1973) and Stoddart (1976) on the
Caribbean], and Maragos (1972) and Grigg (1983) described the ecology of
Hawaiian reef corals. Other reviews include Wells (1957) and Wiens (1962)
on marine biota of Indo-Pacific atolls, and Stoddart (1973) on reef
communities of the Indian Ocean.
Corals and Associated Microflora—
The principal foundation species of coral reef communities, i.e., those
species that contribute the most to community structure (Dayton 1972), are
the hermatypic corals. Reef-building corals provide food and habitat for a
wide variety of organisms (Robertson 1970; Patton 1976). All healthy
hermatypic corals harbor symbiotic zooxanthellae (Dinophyceae), which
apparently contribute substantially to coral nutrition (Muscatine 1973),
reef calcification (Goreau et al., 1979), and primary production (Yonge
1972). Although corals feed extensively on zooplankton (Muscatine 1973),
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they also consume planktonic algae, bacteria, and dissolved organic matter
(Sorokin 1973a, b, c,). After death, the coral skeletons contribute to the
reef framework and sedimentation processes (Stoddart 1969a).
Living corals produce copious amounts of mucus that is used in sediment
rejection and prey capture (Hubbard and Pocock 1972; Lewis 1976). Eventual
release of mucus from the surface of the coral colony results in the
formation of organic aggregates (Johannes 1967). These organic aggregegates
are an energy-rich food source for small reef fishes and possibly
zooplankton (Benson and Muscatine 1974; Ducklow and Mitchell 1979). The
important trophic role of bacteria and detritus in coral reef systems is
discussed by Johannes (1972), Sorokin (1973a, b, c), and Ducklow and
Mitchell (1979).
Competition for space among reef corals has been studied in relation to
light availability, colony growth rates, colony shape, and aggressive
interactions. In general, fast-growing branching species (e.g., Acropora
spp.) may kill smaller colonies indirectly by shading them (Connell 1973).
Massive species in the families Mussidae, Meandrinidae, and Faviidae are
able to inhibit growth of neighboring colonies by extracoelenteric digestion
with mesenterial filaments (Lang 1973; Connell 1973). Lang (1973)
established a competitive aggression hierarchy for western Atlantic species.
Sheppard (1979, 1980a) reported on interspecific aggression,'diversity, and
depth zonation of reef corals of the Chagos Atolls (Central Indian Ocean).
The complexity of interspecific interactions and the unpredictability of
competitive outcomes in nature may limit the extent to which aggression
hierarchies influence coral community structure (Bak et al., 1982).
The principal hermatypic species responsible for coral reef formation
are listed in Table 1 (see Sheppard 1982 for references). In the Atlantic
province, the main reef-forming species is the massive coral Montastrea
annularis. Branching Acropora palmata occurs on seaward slopes and an
encrusting Agaricia/Millepora assemblage occurs in'shallow turbulent areas
(Stoddart 1969a; Glynn 1973). In the Indo-Pacific region, Pocillopora and
Acropora species are most often cited as primary framework builders.
Acropora species are extremely rare in Hawaii (Grigg et al., 1981). There,
Porites compressa, P_. lobata, and Montipora verrucosa assume the role of
dominant reef builders, especially on the well developed reefs of leeward
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TABLE 1. PRIMARY FRAMEWORK BUILDERS OF CORAL REEFS
Species
Site (depth, m)
Atlantic Ocean
Acropora palmata
A. cervicorm's
Forites furcata
Montastrea annul an's
M. cavernosa
i 11epora
poi
TTi
spp.
algae
coralline
Sclerosponges
Indo-Pacific Ocean
Pocillopora damicornis
PocillppoTa spp.
Stylophora pistillata
Acropora pal ifera
A. humilis
7T. Ryacinthus
fcalaxea astreata
Porites californica
Mi 11epora
po
TV
spp.
algae
Coralline
Porites lobata,
Porites compressa,
Montipora spp.
and
Jamaica (0-6)
Florida (0-3)
Bonaire
Lesser Antilles (0-10)
Bonai re
Panama (0-2.5)
Jamaica (6-20+)
Lesser Antilles (6+)
Bonaire
Puerto Rico (8-20)
Lesser Antilles (shallow)
Lesser Antilles (shallow)
Jamaica (70-105)
Panama (0.5-6)
Galapagos
Eilat (0-4)
Chagos (0-4)
N. Great Barrier Reef (0-5)
Lord Howe Is.
N. Great Barrier Reef (5-11)
Chagos lagoon (4-10)
Chagos lagoon (20-30)
Cocos Is.
Eilat (2)
Hawaii and
Atolls
central Pacific
Source: Sheppard (1982) and references therein.
Smith (17 April 1983, personal communication).
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coasts (Maragos 1972; 1973; Grigg 1983). Coral reefs of the Indo-Pacific
generally have a greater number of coral species (total of 700 species) than
those of the Caribbean region (total of 60 species) (Milliman 1973).
Hawaiian reefs are unusual in the Indo-Pacific region in having only 40 to
50 species of stony corals, possibly due to their geographic isolation
(Grigg 1983).
Macrophytes—
The conspicuous macrophytes of coral reefs include coralline algae,
fleshy algae, and seagrasses. The green alga Halimeda is an important
primary producer on coral reefs throughout the tropics (Doty 1973;
Hillis-Colinvaux 1980). Crustose coralline algae, such as Hydro!ithon
reinboldii in Hawaii and several species of Porolithon throughout the
Indo-Pacific, contribute substantially to reef construction (Littler 1973).
Porolithon and to a lesser extent Lithothamnium are the primary components
of the algal ridge zone found at the crest of Indo-Pacific coral reefs
(Stoddart 1969a). Other algae are agents of reef destruction, either
directly by boring into coral skeltons (Highsmith 1981) or indirectly by
overgrowing coral colonies (Banner 1974; Sammarco 1982).
Tropical seagrass beds are often found on reef flats and shallow sandy
terraces adjacent to coral reefs. Seagrass beds serve as foraging grounds
for reef fishes, sea urchins, sea turtles, and manatees; and as nursery
grounds for commercial species such as the pink shrimp Penaeus duorarum,
mullet, sea trout, and stone crab [Zieman (1975) and references therein].
Much of the organic production of seagrass and its associates supports
detritus-based food webs. By acting as baffles against extreme wave action,
seagrass beds also stabilize the substrate and limit sediment resuspension.
Grazers—
The conspicuous grazers of coral reefs include fishes, sea urchins,
manatees, and sea turtles. The conspicuous lack of vegetation cover in many
coral reef habitats can often be attributed to the efficient grazing
activity of sea urchins and fishes (Ogden 1976; Hay 1981). On most reefs,
the main herbivorous fishes are parrotfishes (Scaridae) and surgeon fishes
(Acanthuridae) (Ogden 1976; Goldman and Talbot 1976), and perhaps damsel fish
(Pomacentridae) in shallow back-reef zones (Williams 1981).
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Grazing by urchins and fishes prevents space monopolization by fleshy
algae, which may otherwise overgrow living corals and coralline algae, trap
sediments, and discourage recruitment of coral (Fishelson 1973; Birkeland
1977; Hay 1981, Sammarco 1982). Grazing on seagrasses by fish and urchins
also maintains barren areas, or halos, separating reef borders and adjacent
seagrass beds (Ogden et a!., 1973; Tribble 1981). Algal biomass is usually
greatest where grazing pressure is low, such as on shallow wave-washed
platforms and in deeper areas of the fore reef (Ogden 1976; Benayahu and
Loya 1977; van den Hoek et al., 1975).
The effects of sea urchins and fishes on coral community structure are
complex, depending on grazer abundance and the particular species involved.
For example, grazing by the urchin Echinometra viridis on a patch reef in
Discovery Bay, Jamaica, was highly patchy (up to 50 individuals/m2), whereas
the effects of the urchin Diadema antiVlarum were more uniformily dstributed
at equivalent or lower densities (Sammarco 1982). In the absence of all
urchins, percent cover of adult corals was greatly reduced by algal
overgrowth. However, removal of Diadema alone enhanced coral cover because
this species removes juvenile corals (especially Agaricia and Porites) by
its normal feeding activity. In a back-reef habitat of Discovery Bay,
interference competition by three spot damselfish (Eupomacentrus plam'frons)
promotes coexistence of the two echinoids (I), antillarum and £. viridis) via
habitat partitioning (Williams 1981). Effects of damselfish competition on
urchin densities and distributions may prevent distructive overgrazing of
the coral substate by the echinoids. Finally, exclusion of herbivores from
territories defended by small pomacentrid fishes may result in development
of a thick algal mat, which restricts coral growth and diversity (Vine 1974;
Potts 1977). In some instances, however, pomacentrid territoriality has
been correlated with increased diversity of adult corals (Sammarco 1980).
Wellington (1982) demonstrated that damselfish presence favors branching
pocilloporid corals over massive coral species by protection of
pocilloporids against grazing coral!ivores and by cultivation of algal mats
on massive coral species.
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Predators--
Predators and parasites on living corals include polychaetes,
gastropods, asteroids, echinoids, crustaceans (cyclopoid copepods,
cirripedes, and brachyuran crabs), and fishes (Robertson 1970; Glynn 1982).
Of these, fish and asteroids (discussed below) are probably the most
important. However, predation by the sea urchin Eucidaris on Pocillopora
has been shown to limit the lateral and vertical expansion of Galapagos
coral reefs (Glynn et a!., 1979).
Scarids (parrotfishes) are probably the most important fish predators
on coral populations (Bakus 1972; Frydl 1979), even though predation by
scarids may be incidental to their grazing activity (S.V. Smith, 17 April
1983, personal communication). As with Diadema grazing, the effect of
parrotfishes varies with predator density. At low grazing intensities, the
reef community is dominated by fleshy algae. At intermediate intensities, a
high diversity of corals is found; but with dense parrotfish populations,
coral diversity and cover are low (Brock 1979). Other fishes known to feed
directly on corals include species of triggerfish (Balistidae), filefish or
leather-jackets (Monacanthidae), butterflyfish (Chaetodontidae), and a few
damsel fish (Pomacentridae) and small wrasses (Labridae) (Randall 1974;
Birkeland and Neudecker 1981). Although fish predation on corals may be
greatest in shallow waters above 10 m (33 ft) on some reefs (Bakus 1969,
1972), substantial feeding activity has been reported at depths to at least
65 m (213 ft) (van den Hoek et al., 1975). Control of Pocillopora depth
distribution by fish predation has been suggested by field experiments
(Neudecker 1977, 1979). Fish predation may be instrumental in maintaining
the high diversity of reef corals and other invertebrates (Neudecker 1979;
Ayal and Safriel 1982).
Further information on trophic roles of carnivorous reef fishes is
available in the detailed reviews by Goldman and Talbot (1976) and Sale
(1980). Whether the community patterns of coral reef fishes are determined
by resource partitioning (Anderson et al., 1981) or stochastic events of
recruitment and mortality (Sale and Williams 1982) is undetermined at
present.
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In the Indo-Pacific region, population increases of the asteroid
Acanthaster planci are responsible for widespread mortality of corals
(Endean 1973). On some reefs, Acanthaster may increase coral species
diversity by compensatory mortality of dominant forms (Porter 1972; Colgan
1981), whereas in other areas preferential predation on rare coral species
decreases diversity (Glynn 1974). Survival of Millepora communities,
colonization of dead coral skeletons by algae, and invasions of alcyonarians
have been noted following Acanthaster infestations (Sheppard 1982). Endean
(1973; 1977) has maintained that Acanthaster outbreaks are probably
triggered by extensive collection of molluscan and piscine predators of the
starfish by humans. Other authors have suggested natural causes (Frankel
1977), such as unusually good recruitment of Acanthaster larvae under
optimal conditions of food, temperature, salinity, and predation (Lucas
1973, 1982; Birkeland 1982).
Abiotic Controls on Coral Reef Development
The distribution and growth of coral reefs are influenced by several
abiotic factors, including light availability, salinity, temperature,
turbulence, sedimentation, and dessication. Because of their dependence on
photosynthates produced by zooxanthellae, corals are generally limited by
light availability to depths above 60-100 m (van den Hoek et al., 1975;
Sheppard 1982). Experimental shading of a coral reef for 5 wk decreased
primary production and caused death of corals (Rogers 1979). High turbidity
combined with low salinities and siltation from runoff may also lead to mass
mortalities of reef organisms, especially following periods of excessive
rainfall (Banner 1968). Reef development may be limited by low salinity
(e.g., 25-30 ppt) near river outflows or by high salinity (50-70 ppt) in
arid regions (Wells 1957; Stoddart 1969a). Corals are notoriously sensitive
to thermal variations, and low temperatures (or associated competition from
macrophytes) limit the poleward distribution of most hermatypic species
(Rosen 1981; Sheppard 1982; Johannes et al., 1983). Dessication stress on
reef flats exposed at low tide may favor opportunistic coral species such as
Stylophora pistillata (Loya 1976b, c).
Coral growth is usually greatest on the shallow reef front where waves
and currents prevent excessive sedimentation. Although hydromechanical
stresses limit branching coral species to quieter waters, these forms are
10
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well adapted to heavy siltation rates (Chappell 1980; Sheppard 1982). Heavy
sediment loads produced by dredging restrict reef growth and favor coral
species able to reject settled materials efficiently (Dodge and Vaisnys
1977; Bak 1978).
A semiquantitative model proposed by Chappell (1980) integrates the
effects of natural environmental "stresses" on coral growth forms,
diversity, and reef development (Figure 2). Detailed reviews of ecological
controls on coral populations are available in Stoddart (1969a) and Sheppard
(1982).
SENSITIVITY TO POLLUTION
Coral reef ecosystems are considered extremely sensitive to
environmental perturbations, including various forms of pollution (Johannes
1975; Loya and Rinkevich 1980). The high sensitivity of coral reefs to
pollution stresses is linked to three factors (Johannes and Betzer 1975;
Johnson and Pastorok 1982):
• Narrow physiological tolerance of corals
t Susceptibility of key species interactions to perturbation
(e.g., plant-herbivore relationships, algae-coral
competition)
• Increased effects of toxic pollutants at higher
temperatures.
Corals have extremely narrow tolerance ranges for environmental
conditions (Johannes 1975; Endean 1976). Thus, any variation of
physical-chemical parameters outside their usual narrow range could be
detrimental to coral growth and survival (Endean 1976; Pearson 1981).
Destruction of hermatypic corals by pollution leads to the eventual demise
of many reef species dependent on living corals for food, shelter, and
refuge from predators (Johannes 1975). Through initial disruption of
complex symbiotic relationships, pollution impacts may cascade throughout
the reef system.
11
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Impacts of toxic pollution may be enhanced at high water temperatures
common to coral reef environments (Johannes and Betzer 1975). Documented
effects of high temperatures include increased solubility, faster biotic
uptake, and greater toxicity of pollutants tested.
RECOVERY POTENTIAL
Recovery of coral reef communities from small, localized disturbances
usually requires a decade or less (Table 2; Endean 1976; Pearson 1981).
Small perturbations may increase coral diversity by compensatory mortality
of dominant forms (Porter 1972; Connell 1978), while promoting asexual
reproduction by fragmentation and dispersal of branching forms, e.g.,
Acropora palmata and ^. cervicornis (Highsmith et al., 1980). Following
severe damage, however, hermatypic corals may exhibit negligible
recolonization, even after 20-30 years (Stephenson et al., 1958; Endean
1976). Extreme habitat modification may preclude complete recovery
(Johannes 1975; Endean 1976; Pearson 1981).
Coral recolonization and rates of natural recovery are influenced by:
• Location of damaged habitat
• Size of disturbed patch
t Intensity and frequency of disturbance
• Reproductive "seed" population
• Larval and adult dispersal capabilities
t Current patterns
t Substrate available for larval settlement
t Larval/adult survival and competitive interactions
• Ecosystem productivity.
13
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TABLE 2. ESTIMATES OF CORAL REEF RECOVERY TIME FOLLOWING DISTURBANCE
Disturbance
System
Reef slope—mixed growth
forms, British Honduras
Reef slope — branched and
staghorn corals, FL
Cause
Hurricane
Hurricanes
Magnitude
Large area
Total destruc-
tion
Many 1 ive
corals
rema i ned
Measure of
Recovery
Recolonization
Normal cover
Visual
appearance
Recovery
Time
30 yr average
60-100 yr
maximum
5 yr
2 yr
Reference
Stoddart 1963,
19695, 1974
Shinn 1976
Reef slope—mixed plate Hurricane
and massive corals,
Great Barrier Reef,
Australia
Reef slope—reefs on Volcanic
submerged lava, HI
Reef slope—branching and Cold
massive corals,
Persian Gulf
Major storm
Colonization
of sterile
habitat
Acropora damage
Massive corals
unaffected
Good coverage
of well dev-
eloped colonies
Percent cover
No. species
Diversity
Recolonization
Visual
appearance
<20 yr
20 yr exposed
50 yr sheltered
4 yr
Woodhead (App. E
in Walsh et al.,
1971)
Grigg and
Maragos 1974
Shinn 1976
Reef slope—Gulf of Mexico Red tide
Reef flat—Guam
Low tide
Most fish,
corals, other
invertebrates
died
Mass mortali-
ties, including
corals
Recolonization -vl yr
of small
colonies
Recolonization >3 yr
Normal cover
Smith 1975
Yamaguchi 1975
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TABLE 2. (Continued).
System
Reef flat— Red Sea
Patch reef— tabular
Acropora, Enewetak Atoll
Reef front, terrace, and
slope—Guam
Reef lagoon— Arno Atoll,
Marshall Islands
Reef slope— Innisfall ,
Queensland
Reef slope— Feather Reef,
Queensland
Disturbance
Cause Magnitude
Low tide 80 to 90% coral
mortality
Nuclear Total mortality
blast Skeletons left
intact
Acanthaster 30% decrease
in number of
species
>50% decrease
in coral cover
Acanthaster Most coral
died
Acanthaster Extensive
coral
mortalities
Acanthaster Extensive
coral
mortalities
Measure of
Recovery
Return to pre-
vious community
structure
Regrowth of
dominant coral
Diversity
Percent cover
Colony size
Growth forms
Recolonization
of small
colonies
Percent cover,
No. colonies,
No. species
Recruitment of
young colonies
Community
structure
Recovery
Time
5-6 yr
>13 yr
20 yr subtidal
terrace
31 yr seaward
slope, possibly
100' s yr
3 yr
>8 yr
<6 yr
>12 yr
Reference
Loya 1975, 1976b
Johannes 1975
Randall 1973
Branham 1973
Pearson and
Endean 1969
Pearson 1974,
1981
Pearson and
Endean 1969
Pearson 1981
-------
TABLE 2. (Continued)
System
Great Barrier Reef--
Australia
Tangulsson Reef--
Guam
Disturbance
Cause Magnitude
Acanthaster Extensive coral
mortalities
Acanthaster Major reduction
in species rich-
ness, density
and cover of
corals
Measure of Recovery
Recovery Time
Community 20-40 yr
structure
Community 12 yr
structure
Reference
Endean 1971,
1973, 1976
Colgan 1981
Several coral reefs--
Various locations
Floods
Volcanic
water
Dredging
Extensive
often complete
mortalities
of corals
Recolonization
of small
colonies
No recovery
>30-50 yr
Endean 1976
Pearson 1981
-------
In general, recovery of coral reef communities may be fastest on the
reef flat and the shallow reef front, and slowest in the coral lagoon and
seaward reef slope zones (Pearson 1981; Johnson and Pastorok 1982). Life
history strategies of dominant species and key trophic interactions
influence the initial response to natural or anthropogenic perturbations as
well as the direction and timing of recovery (Loya 1976b, c; Pearson 1981;
Highsmith 1982; Porter et al., 1982). For example, recovery of exposed
coral reefs which are dominated by early successional communities is usually
more rapid than recovery of sheltered reefs where communities are closer to
"climax" associations (Grigg and Maragos 1974; Table 2). Opportunistic
species occupy disturbed habitats in lieu of "climax" community taxa (Loya
1976c). Finally, recovery of corals may be delayed if depression of grazer
populations allows space monopolization by benthic algae (Fishelson 1973;
Birkeland 1977; Sammarco 1982).
17
-------
IMPACTS OF SEWAGE DISCHARGES
The effects of sewage discharges on coral reef communities are
discussed in the following sections. After a brief discussion of potential
impacts, a summary of case histories is presented.
POTENTIAL IMPACTS
The potential impacts of sewage effluent on coral reef communities may
be broadly classified into four categories: 1) oxygen consumption, 2)
nutrient enrichment, 3) sedimentation, and 4) toxicity.
Oxygen Consumption
Most tropical organisms, including corals, are living in environments
near their critical tolerance levels for dissolved oxygen (Kinsey 1973).
Hence, oxygen utilization by organic matter and microbes in sewage effluent
"may constitute a significant stress" (Johannes 1975). Note that depression
would be most critical at night, when oxygen levels are usually at their
daily lows. Kinsey (1973) indicated that reef communities maintained a
constant rate of oxygen consumption (respiration) as ambient dissolved
oxygen levels declined to zero in field experiments. However, isolated
corals may decrease their respiration rates to survive short periods of
hypoxia (Yonge et al., 1932).
Nutrient Enrichment
Nutrient enrichment of coastal waters by sewage effluents can lead to
dramatic modifications of physical, chemical, and biological parameters
(Smith et al., 1981). Johannes (1975) summarizes the effects of
anthropogenic nutrient inputs on reef communities and provides a discussion
of "eutrophication-loving" organisms. Various aspects of enrichment are
discussed more fully in later sections of this report.
18
-------
Sedimentation
Sedimentation of sewage solids may result in accumulation of
organic-rich deposits around outfalls located in poorly flushed waters
(Maragos 1972). Resuspension of sediments and direct deposition of sewage
particles on coral colonies could produce a variety of stresses including
reduced light availability, enhanced bacterial populations, and the
expenditure of additional energy to remove sediment from the colony surface
(Roy and Smith 1971; Johannes 1975; Walker and Ormond 1982). Sedimentation
impacts are treated in detail later (see below, Impacts of Sedimentation).
Toxicity
Toxic effects on corals and other reef organisms may result from
chemicals present in sewage effluents (e.g., chlorine, phosphate,
pesticides, PCBs, metals, and petroleum hydrocarbons) or release of hydrogen
sulfide from anaerobic sediments. Although toxic substances contained in
sewage effluents are potentially harmful to reef communities, their effects
have received little investigation (but see, e.g., Davis 1971 as cited by
Johannes 1975; Sorokin 1973c; Olafson 1978; Kinsey and Davies 1979; Loya and
Rinkevich 1980).
CASE HISTORIES
The available case histories of sewage effects on coral reefs are
summarized in Table 3. It is apparent that few detailed studies have been
conducted.
Short-term studies conducted within a year after initiation of small
sewage discharges reveal minor physical damage associated with outfall
construction, but little evidence of coral community impacts has been found
(e.g., Tsuda et al ., 1975; Amesbury et al., 1976). Although algal
populations may increase rapidly in response to sewage enrichment,
community-level impacts on corals may require a year or more for development
after initiation of the discharge. The most common response to high sewage
loading is an increase in benthic algae and filter-feeding invertebrates
(e.g., bryozoa, sponges, and tunicates), with a corresponding decrease in
the diversity and abundance of hermatypic corals (Maragos 1972; Smith et
19
-------
TABLE 3. CASE HISTORIES OF SEWAGE DISCHARGE IMPACTS ON CORAL REEFS
ro
o
Discharge Characteristics
Location
Aqaba, Jordan
Fringing reef
Gulf of Aqaba,
Red Sea
Pt. Gabert outfall
Atoll lagoon reef
Moen, Truk
Effluent Mass
Flow Emissions
0.0004- ,
0.0007 m-Ysec
(0.010 -
0.015 MGD)
Distance
Depth from Reef Other
on reef 200-400 tons apatite
per year. Primary
treated sewage
8.4 m on reef Secondary treatment.
(27.6 ft) Diffusers located on
sand/silt substrate
with little coral cover
Reported Effects
Higher death rate of coral
Stylophora pistil Tata 1n polluted
area. Elevated algal and grazer
abundance near outfall
No apparent effects on corals,
algae, fish, and zooplankton3
Reference
Walker and Ortnon
(1982)
Tsuda et al .
(1975)
Tourist hotel
outfalls, Fringing
reefs, Northern
coast, Jamaica
Oonltsch outfall
Lagoon fringing
reef, Yap,
W. Caroline Is.
Halanae outfall
Fringing reef
Oahu, Hawaii
H1lo outfall
Patch reefs,
Hilo Bay
Oahu, Hawaii
Hokapu outfall
Fringing reef
Oahu, Hawaii
varied
many on
reef
6m on reef
(20 ft)
0.053 m3/sec
(1.2 MGD)
0.131 m3/sec
(3.0 MGD)
0.425 m3/sec
(9.7 MGD)
204 kg/day
annual
average
(450 Ib/day)
793 kg/day
(1,760 lb/
day) end of
permit
1,175 kg/day
(2,591 lb/
day)
10.4 in
(34 ft)
17 m
(56 ft)
27.1 -
33.2 m
(89 - 109
ft)
on reef
adjacent
to reef
outcrops
on reef
Varied treatment and
suspended solids
Preoperational data
only
Primary treatment.
No industrial flow
Primary treatment
Primary and
trickling filter
treatment. No
Industrial flow
Possible Impacts of detergents,
nutrient enrichment, solids deposi-
tion, and bacterial contamination
were noted3
Damaged corals and seagrass beds
due to outfall construction. In-
creased number of fish species in
rubble and seagrass zones, de-
creased number of fish species in
coral-dominated zones3
No apparent effects on corals,
mlcromolluscs, and zooplankton3'
Higher biomass of frondose algae
and Increased abundance of fish
at outfall3
Although coral cover near the out-
fall was lower than that at the
control site, sewage was considered
less important than other stresses3
Decreased abundance of micro-
molluscs and coral from preopera-
tional to postoperational
period3* . Increased chlorophyll
£, blue-green algae, and fish
Barnes (1973)
Amesbury et al.
(1976)
Reed et al.
(1977)
Bowers (1979a)
Tetra Tech
(1982c)
Bowers (1979b)
Tetra Tech
(1982a)
Russo et al.
(1977, 1979)
Russo (1982)
Tetra Tech
(1982b)
-------
TABLE 3. (Continued).
Kaneohe Bay
outfalls, Lagoon
fringing and
patch reefs,
Oahu, Hawaii
Sand Island
outfall , Fringing
reef, Oahu,
Hawaii
0.2-0. 3d m3/sec
(5-8° MGD)
2.98C m3/sec
(68. Oc MGD)
Similar to
Mokapu
outfall
21,000C
kg/day
(46,000C
Ib/day)
7 m
Marine
Corps
Station
8 m
Kaneohe
Municipal
It m
(35 ft)
lagoon Predlverslon and post-
adjacent diversion data.
to reef Mainly secondary
treatment. Two out-
falls and nonpoint
sources
on reef Raw sewage discharge,
1955-1977
Enhancement of chlorophyll a and
zooplankton biomass. Decline of
coral reefs due to overgrowth of
benthlc green algae and filter-
feeders (bryozoans, sponyes,
tunicates, etc.)
Complete absence of reef corals,
enhancement of polychaete
(Chaetopterus) populations within
400 m of outfall. Diversity of
corals and other benthos enhanced
in intermediate Impact zone
Marayos (1972)
Banner (1974)
Caperon et al .
(1976)
Laws and Redalje
(1979, 1982)
Smith et al .
(1981)
Dollar (1980)
Grigy (1975)
Tetra Tech (1980)
a Study design or survey methods places limitations on reliability of data.
b Reduced percent cover of corals attributed to inconsistency 1n transect locations rather than sewage impact.
c Values for new deep water outfall only.
d End of operational period. See Figure 3 below.
-------
al., 1981; Walker and Ormond 1982). In well-flushed waters along an open
coast, few significant effects of sewage on coral reef communities have been
demonstrated (Bowers 1979a, b; Russo et al., 1977, 1979; Russo 1982).
However, the data from these latter studies on the response of corals is
limited by improper study designs and small sample sizes.
Two case histories, the Gulf of Aqaba (Red Sea) and Kaneohe Bay
(Hawaii) illustrate significant effects of sewage on coral reef communities.
These studies are reviewed in detail below.
Gulf of Aqaba, Red Sea
The dynamics of coral mortality and algal growth resulting from sewage
pollution have been studied on a fringing coral reef near Aqaba, Jordan
(Walker and Ormond 1982). The reefs are potentially affected by a sewage
discharge and by sediment deposition from an apatite ore loading facility.
Although the relative importance of sewage pollution and apatite loss from
ships was not determined, spatial effects of the sewage discharge were
apparent. An increase in algal cover, a decrease in coral diversity, and an
increase in small grazing molluscs were "obvious" from 5 m "upstream" to
about 50 m "downstream" of the outfall. Walker and Ormond (1982) found that
the death rate of coral tissue near the outfall was 4-5 times the death rate
observed in a control area. Stylophora pistillata, a fast-growing
opportunistic species (Loya 1976c), was the only remaining abundant coral
species. Dead portions of colonies were covered with filamentous algae.
Although biomass of algae (mainly Ulva 1actuca and Enteromorpha
clathrata) was elevated at the outfall site compared with the control area,
algal overgrowth did not appear to be a direct cause of coral death.
Mortality was possibly related to inhibition of calcification by high
phosphate concentrations, stress caused by high sediment loads, or localized
bacterial infection triggered by the sewage effluent. Because grazer
populations were higher at the sewage area compared to the control site,
Walker and Ormond (1982) attributed the excessive algal growth to nutrient
enrichment rather than a relaxation of grazing pressure. The authors
concluded that the effect of increased sediment loads near the outfall were
greatly aggravated by the ability of the algal mats to trap sediment,
resulting in further stress to adjacent coral tissues.
22
-------
Kaneohe Bay. Hawaii
Kaneohe Bay, located on the northeastern side of Oahu In the Hawaiian
Islands, received sewage Inputs for a period of about 30 years (Laws 1981).
After a period of increasing sewage discharge rates from 1950-1977,
wastewaters from the Kailua-Kaneohe and Marine Corps treatment plants were
diverted to an open ocean outfall off Mokapu Point (Figure 3). The effects
of sewage enrichment on coral reef communities in Kaneohe Bay and their
initial recovery following diversion of wastewaters are particularly well
documented (e.g., Maragos and Chave 1973; Banner 1974; Laws and Redalje
1979, 1982; Smith et al., 1981). Although other impacts of urbanization
such as dredging, Increased runoff, and sedimentation complicated the
initial interpretation of sewage discharge effects, (Banner 1974), the
Kaneohe Bay diversion project offered an unprecedented opportunity for
evaluation of sewage impacts on coral reef ecosystems (Smith et al., 1981).
Biological changes following wastewater diversion are interpreted as a
reversal of sewage impacts.
Physical Setting--
Kaneohe Bay is a semienclosed embayment, with a barrier reef extending
along much of the bay mouth (Figure 4). The bay is divided longitudinally
into four sectors on the basis of urban influence (especially sewage
inputs), with increasing urbanization from north to south. The area of the
inner bay is 31 km2 (12 mi2), and the mean depth varies from 5.0 m (16.4 ft)
in the outfall (OF) sector, where the two major sewage discharges were
located, to 10.2 m (33.5 ft) in the southeast (SE) sector (Smith et al.,
1981). A variety of coral reef and lagoon habitats are found in Kaneohe Bay
(Smith et al., 1981).
Water enters the bay primarily across the broad barrier reef at the bay
mouth, then moves into the southern basin from the central sector (Bathen
1968; Smith et al., 1981). In the inner central (CE) and northwest (NW)
sectors, the predominant flow is from the south to the northwest. Water
exits from the bay primarily through two deep channels, one north and one
south of the barrier reef. Because the SE sector is largely isolated from
direct oceanic exchange by Coconut Island and a system of shallow reefs,
23
-------
U3
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VO 3
ro
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CX3
Cu
Ql
3
Q.
C
OJ
00
Ol
THOUSANDS OF CUBIC METERS/DAY
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7-
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Z
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a
z
•0
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F S
r o
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f^ m 0)
m z 5
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GO
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-------
CORAL REEFS
KANEOHE WASTEWATER TREATMENT
PLANT OUTFALL
KANEOHE MARINE CORPS
AIR STATION SEWER OUTFALL
MOKAPU POINT SEWER
OUTFALL
WATER QUALITY AND
PLANKTON SAMPLING SITES
BENTHOS BIOMASS AND/OR
METABOLISM TRANSECTS
LAGOON-FLOOR METABOLISM SITES
LINES SEPARATE SECTORS OF BAY
SOURCE adapted from Smitri et al , 1981
J NAUTICAL MILES
KILOMETERS
Figure 4. Location of coral reefs and prediversion/postdiversion
sampling stations, Kaneohe Bay, Hawaii.
25
-------
water circulation is restricted compared to the CE and NW sectors.
Nevertheless, tidal flushing is efficient, yielding residence times of about
24 days for the SE sector and 12 days for the rest of the bay (Sunn, Low,
Tom, and Hara, Inc., 1976). From a model of tidal flushing in Kaneohe Bay,
Smith et al. (1981) calculated a flushing time of 8 days for the entire bay
and 13 days for the southern basin (SE and OF sectors combined).
Impacts of Sewage—
The quantity of sewage wastewater entering Kaneohe Bay from 1950
through 1979 is shown in Figure 3. From 1963 on, the bulk of the
wastewaters discharged to the bay resulted from secondary sewage treatment.
Water Quality and Plankton—About 74 percent of the nitrogen and 75
percent of the phosphorus influx to Kaneohe Bay was contributed by sewage
discharges from the Kaneohe municipal and Kaneohe Marine Corps Air Station
treatment plants (Sunn, Low, Tom, and Hara, Inc., 1976). The main effects
of nutrient enrichment on water quality and plankton were:
• Increased concentrations of inorganic phosphorus and
particulate nitrogen: the average concentration of each
nutrient in the outfall sector was almost four times that in
the rest of the bay (Laws and Redalje 1979).
• Reduced water clarity (Laws and Redalje 1979; Smith et al.,
1981).
t Enhancement of phytoplankton biomass and total primary
productivity: e.g., average chlorophyll a_ near the outfall
was 6.7 times the average value for the central and
northwest sectors combined (Caperon et al., 1976; Laws and
Redalje 1979; Smith et al., 1981).
t Appearance of "red tides:" e.g., Exuviella sp. near the
outfall and throughout the south sector (Clutter 1972).
t
Minor enhancement of zooplankton biomass, with a decrease in
species diversity (Clutter 1972; Smith et al., 1981).
26
-------
Other parameters showed little change with distance from the sewage
outfalls or little response to sewage diversion. For example, average
dissolved oxygen concentrations for the period January, 1976, to June, 1977,
were similar throughout Kaneohe Bay, with the lowest time-averaged value of
94 percent saturation in the outfall sector (Smith et al., 1981). Inorganic
nitrogen levels were insensitive to sewage loading because of rapid uptake
in a nitrogen-limited system (Laws and Redalje 1979, 1982; Smith et al.,
1981).
Benthic Invertebrates and Macrophytes—The primary impacts of sewage on
benthic communities in Kaneohe Bay included:
• Decreased coral cover, taxonomic richness, and net
calcification rate (Banner 1974; Kinsey 1979; Smith et al.,
1981).
t Increased biomass of algae Ulva and Hydroclathrus in OF/SE
sectors and bubble algae Dictyosphaeria cavernosa throughout
the CE sector (Soegiarto 1973; Banner 1974; Smith et al.,
1981).
t Shift of benthic community structure away from corals and
associates toward filter feeders such as sponges and
zoanthids (Maragos 1972; Smith et al., 1981)
In addition, the diversity of benthic algae in the southern basin may have
been reduced, as indicated by the absence of common lagoon algae (Soegiarto
1973). Despite this trend and the spatial gradient of increasing coral
species richness away from the south basin (Maragos 1973; Maragos and Chave
1973), Smith et al. (1981) concluded that sewage inputs did not cause major
shifts in species composition of the benthos.
The effects of nutrient loading on coral communities in Kaneohe Bay can
be attributed to several mechanisms (Maragos and Chave 1973; Laws 1981;
Smith et al., 1981). First, abundant phytoplankton in the sewage enriched
waters of the southern basin reduced light availability to coral
zooxanthellae, probably resulting in poor nutrition, growth, and survival of
27
-------
corals. Second, enhanced production of organic particles favored benthic
filter-feeders. Living corals transplanted to the south bay were quickly
outcompeted by tunicates, bryozoans, sponges, sabellids and other
filter-feeders (Maragos 1972). Third, the low diversity of corals and other
benthos in southern Kaneohe Bay was attributed in part to the toxicity of
hydrogen sulfide in anoxic bottom sediments (Maragos and Chave 1973).
Maragos (1972) found that the survival time of transplanted corals was
directly proportional to distance from the sewage outfalls. Moreover,
Sorokin (1973c) indicated that sulfide levels increased and the anaerobic
layer expanded closer to the Kaneohe sewage outfall.
Finally, sewage influenced the coral reefs of central Kaneohe Bay
indirectly by stimulating growth of Dictyosphaeria cavernosa (Smith et al.,
1981). This green bubble algae kills corals (mostly Porites compressa) by
forming thick mats which smother all underlying reef organisms (Maragos and
Chave 1973; Banner 1974). As a result of grazing pressure and better
flushing in the northwest sector, D. cavernosa failed to dominate benthic
communities there. Bubble algae were rare in the southern basin (Soegiarto
1973), probably for the same reasons corals are absent (Maragos and Chave
1973). Smith et al. (1981) presented experimental evidence that light
limitation was one important factor restricting growth of ]3. cavernosa in
the outfall (OF) sector.
In the lagoon area of Kaneohe Bay, Maragos (1972) calculated that 8.5
percent of the living reef front was killed by the direct effects of sewage
discharge, 23.5 percent was overgrown by Dictyosphaeria cavernosa, 29.3
percent was removed by dredging, and 9.8 percent was destroyed by freshwater
influx and sedimentation. Further, he estimated that 26.4 percent of the
reef fronts in the northern sector have died, 86.8 percent in the central
sector, and 99.9 percent in the southern sector.
Fishes—The fish communities on reef slopes and crests exhibit
substantial differences among the various sectors of Kaneohe Bay. Species
richness is lowest in the southern basin (6 resident species) compared with
the central (43 resident species) and northern sectors (40 resident species)
(Smith et al., 1981). Presumably, this pattern results from the reduced
habitat complexity of the southern sector due to the absence of living
corals. In contrast, the species richness of fishes associated with the
lagoon floor does not vary among sectors.
28
-------
Planktivorous fishes (e.g., Stolephorus purpureus and Pranesus
insularum) were more abundant in the southern basin than in the rest of the
bay (Clarke 1973), perhaps due to enhancement of prey populations near the
sewage outfalls. By the late 1970s, planktivorous species dominated fish
communities of the central sector (Brock et al., 1979). In contrast, other
reefs are generally dominated by predators on larger prey (Goldman and
Talbot 1976). Some common reef dwellers (e.g., Stethojulis, Scarus.
Acanthurus, and Chaetodon spp.) were rare in the southern sector (Key 1973).
Ecosystem Response to Sewage Diversion-
Diversion of sewage from Kaneohe Bay outfalls to the Mokapu outfall
occurred in two stages: 1) the diversion of the Kaneohe discharge in
December, 1977 and 2) the diversion of the Marine Corps discharge in May,
1978. The study by Smith et al. (1981) spanned a prediversion period
(January 1976 through November 1977) and a "postdiversion" period (December
1977 through August 1979).
The responses of physical, chemical, and biological parameters to
sewage diversion in Kaneohe Bay are summarized in Table 4 and Figure 5.
Smith et al . (1981) evaluated the responses of biomass, nutrient
concentrations, and rate parameters quantitatively as the percent decrease
in the average value of each parameter for the southern basin (i.e., sector
nearest the outfall) from the prediversion survey to the postdiversion
survey. Water column variables were volume-averaged (Smith et al., 1981).
A spatial gradient for the postdiversion period was determined as the ratio
of a mean parameter value at Station OF to an average transition zone value
(i.e., volume- or area-weighted means for stations NW and CE). Since
detailed taxonomic identifications were not performed, changes in community
structure were evaluated subjectively (e.g., Table 4).
Parameter responses to sewage diversion fall into three groups (Figure
5):
1. Moderate Response to Sewage Diversion, Moderate Spatial
Gradient:
29
-------
TABLE 4. SUMMARY OF RESPONSES TO SEWAGE DIVERSION,
KANEOHE BAY, HAWAII
Diversion Response3 Spatial Gradient
Variable (Percent) Responseb
Quantitative Variables
Dissolved inorganic nitrogen 37 1.4
Dissolved inorganic phosphorus 70 1.8
Participate organic carbon 36 1.3
Phytoplankton biomass 37 2.3
Phytoplankton growth rate 36 1.0
Macroplankton dry weight 35 2.7
Microplankton ash-free dry weight 35 1.9
Hard bottom algal biomass 62 0.2
Hard bottom cryptofaunal biomass 76 2.5
Lagoon floor biomass 83 0.4
Lagoon floor nitrogen release 42 1.3
Extinction coefficient 25 1.8
Detritus 8 1.2
Qualitative Variables:
Community Structure
Zooplankton slight moderate
Benthic algae slight to moderate slight
Benthic macrofauna slight or none moderate
Fish none? large
a Percent decrease in the southern basin (volume-weighted means of the
southeast and outfall sectors of the bay).
b Ratio of post diversion values in the outfall sector to values in the
transition zone (volume- or area-weighted means of central and northwest
sectors).
Source: Smith et al. (1981).
30
-------
PERCENT DECREASE
UJ
UJ
O
<
cr
o
O
to
cc
o
LINES DELINEATE THREE RESPONSE
GROUPS DISCUSSED IN TEXT
NONE
MODERATE
LARGE
DIVERSION RESPONSE
DIN = Dissolved inorganic nitrogen
DIP = Dissolved inorganic phosphorus
POC = Paniculate organic carbon
PB = Phytoplankton biomass
PGR = Phytoplankton growth rate
MAPW = Macroplankton dry weight
MIPW = Microplankton ash-free dry weight
HBAB = Hard bottom algal biomass
HBCB = Hard bottom cryptofaunal biomass
LFB = Lagoon floor biomass
LNR = Lagoon floor nitrogen release
EC = Extinction coefficient
D = Detritus
Z = Zooplankton
BA = Benthic algae
BM = Benthic macrofauna
F = Fish
• Quantitative variables
O Qualitative variables
See footnotes to Table 4
SOURCE: Smith etal., 1981 (modified)
Figure 5. Spatial gradient and parameter responses to sewage
diversion, Kaneohe Bay, Hawaii.
31
-------
Dissolved inorganic nitrogen (DIN)
Participate organic carbon (POC)
Phytoplankton biomass (PB)
Phytoplankton growth rate (PGR)
Macroplankton dry weight (MAPW)
Lagoon floor nitrogen release (LNR)
Extinction coefficient (EC)
2. Large Response to Diversion, Wide Range of Spatial
Gradients:
Dissolved inorganic phosphorus (DIP)
Hard bottom algal biomass (HBAB)
Hard bottom cryptofaunal biomass (HBCB)
Lagoon floor biomass (LFB)
3. Slight Response to Diversion, Small to Large North-South
Gradient:
Detritus (D)
Zooplankton structure (Z)
Benthic algal structure (BA)
Benthic macrofauna structure (BM)
Fish structure (F).
Variables in Group 1 include all of the water column mass parameters
(except dissolved inorganic phosphorus). The various particulate and
dissolved inorganic materials, phytopiankton, and microheterotroph masses in
Group 1 exhibited gradients from high concentrations near the outfall to low
values in the northern basin (Smith et al., 1981). These parameters
decreased rapidly within the 1-2 yr following sewage diversion, possibly
declining to baseline values (Smith et al., 1981). However, Laws (1981) and
Laws and Redalje (1982) indicated that nutrients released from organic-rich
sediments may have continued to support chlorophyll a^ biomass and nutrient
levels above baseline values throughout the postdiversion period.
The second group of variables, including dissolved inorganic phosphorus
and several benthic biomass measures, showed a large response to sewage
32
-------
diversion (Table 4; Figure 5). Because the Kaneohe Bay system was far from
phosphorus limitation before sewage diversion, the response of phosphate was
large (Smith et a!., 1981). The large response of benthic biomass variables
to diversion reflected the decreased influx of particulate matter to the
benthos compared with that contributed from a water column previously
enriched with sewage nutrients. However, Smith et al., (1981) reported that
benthic conditions at the end of their postdiversion survey did not match
the "presewage" baseline. This result was attributed in part to the
destruction or burial of hard substrate habitat by both "sewage-mediated
biological activity" (e.g., overgrowth of corals by bubble algae) and heavy
siltation from urban runoff. Moreover, the slow recruitment processes
necessary for re-establishment of coral populations (see above,
INTRODUCTION, Recovery Potential) precludes rapid succession and recovery of
reef communities. By mid 1981, partial recovery of the coral communities
was evident (Smith et al., 1981).
The third group of variables showed little response to sewage
diverison. In Kaneohe Bay, the detrital pool was maintained by runoff and
sediment resuspension, not by nutrient input from sewage. The slight change
in community structure variables from prediversion to postdiversion periods
may indicate that the effects of sewage inputs were minor. Alternatively,
the benthic habitat may not have had sufficient time to return to a
predischarge condition (Smith et al., 1981). Disintegration of reef rock,
which was linked to shifts in reef community metabolism caused by the
discharge, may account for the delay in recovery.
33
-------
IMPACTS OF SEDIMENTATION
Quantitative measurements of solids deposition rates are generally
unavailable for sewage discharges in coral reef environments. Consequently,
the following discussion emphasizes sedimentation of particulate matter
derived from terrestical runoff, dredging and filling activities, and
resuspension of bottom sediments.
POTENTIAL IMPACTS
The effects of sediment inputs to a coral reef environment depend
primarily upon the relative'senstivities of the primary framework species.
Sensitivity of Corals to Sedimentation
The sensitivity of a coral species to rapid sedimentation depends on
the sediment-trapping properties of the colony and the ability of individual
polyps to reject settled materials. Horizontal plate-like colonies and
massive growth forms present a large, stable surface for interception and
retention of settling solids. Conversely, vertical plates and upright
branching forms are less likely to retain sediments on the surface of the
colony (Bak and Elgershuizen 1976; Dryer and Logan 1978; also see above
Figure 2). Tall polyps and convex colonies are also less susceptible to
sediment accumulation than are other growth forms (Lasker 1980).
The physical and chemical characteristics of the sediment are also
important determinants of its effects on reef biota. Physical
characteristics such as density and grain size composition may influence
clearing rates within a given species. Sediment chemistry is also critical:
sediments having high organic content, high BOD, or adsorbed toxic
substances (e.g., pesticides) may exert more pronounced effects on the
behavior and physiology of reef organisms than would less chemically active
sediments (e.g., calcium carbonate, quartz) of the same grain size
composition.
34
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Lastly, sensitivity of corals to sedimentation may be influenced by the
frequency of exposure to suspended solids, and the light attenuation which
results from decreased water clarity. The occasional dosing of corals with
sediments advected into the reef area (primary sedimentation) may be less
harmful than repetitive dosing with resuspended sediments. Aside from
differences in energy expended to clear sediments, rapid light attenuation
with depth, which accompanies turbid conditions, may also affect
photosynthesis by the zooxanthellae. This effect may be most pronounced in
relatively clear waters, where the addition of a small amount of suspended
material greatly decreases light transmittance. In systems where ambient
turbidity is relatively high, a small increase in suspended material will
have little effect on light transmittance.
Sediment Rejection-
Coral polyps reject sediment landing on the surface of the colony by
four mechanisms: 1) polyp distension by uptake of water through the
stomodeum, 2) tentacular movements, 3) ciliary action, and 4) mucus
production (Marshall and Orr 1931; Hubbard and Pocock 1972). Although the
efficiency of sediment rejection has been related to skeletal geometry and
polyp morphology (Hubbard and Pocock 1972; Loya 1976a), polyp behavior may
supercede morphological differences (Bak and Elgershuizen 1976).
Several factors limit the ability of corals to reject sediment. First,
most coral colonies are unable to coordinate transport of sediment off the
colony by the shortest possible route. The pathway followed by a sediment
particle during the rejection process approximates a random walk (Dodge and
Vaisnys 1977). Thus, the sediment rejection process is much more efficient
in small or young corals than in large or old colonies. Second, silt is the
largest particle size effectively removed by many coral species {Hubbard and
Pocock 1972). Larger size fractions, which are removed by some species but
not others, must be transported by polyp distension rather than relatively
weak ciliary action.
35
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Relative Species Sensitivity—
The relative sensitivities of some coral species to sedimentation
effects are given in Table 5. Only those species which have a clear
sensitivity ranking have been included in the table. The relative
sensitivity of a few genera is given to illustrate the variation in rank
among species within a genus (e.g., the common genera Acropora, Porites,
Pocillopora). In general, coral species inhabiting the seaward margins of a
reef are less tolerent of high sediment loads than species found in
nearshore areas (Vaughan 1916; Marshall and Orr 1931; Stern and Stickle
1978).
Montastrea cavernosa is able to effectively reject sediments at
deposition rates as high as 7-8 mg cm'2 day"2 (Lasker 1980). The upper
limit to M. cavernosa's ability to remove sediment effectively appears to be
about 14 mg cm'2 day"1 or slightly higher (Loya 1976a, Lasker 1980). Since
M_. cavernosa is an efficient sediment rejector and is commonly found in
environments dominated by rapid sediment accumulation, many other coral
species are less tolerable of heavy sediment inputs.
Individual Effects
High concentrations of suspended solids and rapid sedimentation are
responsible for decreased coral growth rates, changes in colony growth form,
and possibly increased mortalities.
Lethality—
A heavy coating of sediments or complete burial for more than several
hours kills most corals (Edmondson 1928; Marshall and Orr 1931; Roy and
Smith 1971).
Growth Inhibition-
Adverse effects of heavy sediment loads on coral growth may result from
decreased light availability, abrasion, and energy expenditure for sediment
rejection. High turbidity interferes with light penetration to the bottom
and thereby limits photosynthesis of zooxanthellae and coral growth (Roy and
36
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TABLE 5. SENSITIVITY OF SOME COMMON CORAL
SPECIES TO SEDIMENTATION
Sensitivity
Species Low Moderate High
Montastrea cavernosa x
Siderastrea radianT" x
Siderastre? siderea x
Manicina areolatax
Fungi a spp. x
Agancia agaricites x
Acropora hyacinthu? x
Acropora corymbosa" x
Acropora cerviconn's x
Other Acropora spp. x
Pori tes astreoides x
Other Porites spp. x x
Pocillopora spp. x x
Source: Edmondson (1928), Marshall and Orr
(1931), Yonge (1935), Hubbard and Pocock
(1972), Ott (1975), Bak and Elgershuzien
(1976), Loya (1976a), Bak (1978), Lasker
(1980).
37
-------
Smith 1971; Maragos 1972; Dallmeyer et al., 1982). Experimental additions
of peat particles to field enclosures decreased primary production and
reduced chlorophyll content by 22 percent in Montastrea annularis,
indicating loss of zooanthellae from stressed corals (Dallmeyer et al.,
1982). Calcification rates have been reduced by as much as 40 percent by
natural resuspension of sediments (Dodge et al., 1974) and by as much as 33
percent by short-term dredging impacts (Bak 1978). Although some coral
species (e.g., Montastrea cavernosa, Siderastrea siderea) are able to
survive highly turbid conditions (Roy and Smith 1971; Loya 1976a; Randall
and Birkeland 1978), reduction of light levels below the critical
compensation point for photosynthesis may lead to cessation of growth and
eventual death, especially in deepwater corals (Johannes 1975).
Abrasion of coral surfaces by suspended particulates may also
contribute to decreased growth (Johannes 1975 and references therein; Loya
1976a). Wiens (1962) concluded that mechanical scour plays a role in the
destruction of coral reefs, particularly at the reef margins.
Rejection of sediments by corals is an energetically-expensive process.
Dallmeyer et al. (1982) demonstrated a significant increase in coral
respiration rates during vigorous sediment-cleansing activities. Energy
required for sediment removal is diverted from other metabolic functions,
possibly leading to reduced growth and lower reproductive output (Aller and
Dodge 1974; Dodge and Vaisnys 1977; Dallmeyer et al., 1982). Moreover, if
coral polyps are occupied with sediment rejection activities, they may be
unable to capture zooplankton effectively.
Growth Form Changes-
Aside from its effects on the rate of coral growth, rapid sedimentation
is expected to produce changes in the growth form of coral colonies.
Differential accumulation of sediment across the surface of a colony
influences topographical variations in growth rate, possibly modifying
colony growth towards forms more resistant to sedimentation (Marshall and
Orr 1931; Roy and Smith 1971).
38
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Population and Community Effects
Adverse impacts of sedimentation on coral populations and communities
are evidenced by changes in the relative abundances of coral species,
reduced substrate cover by living corals, lowered species diversity, and
inhibition of larval recruitment.
Disturbance of Community Structure-
Healthy coral communities may exist in chronically turbid waters,
especially when strong currents prevent the build-up of sediments on coral
surfaces (Marshall and Orr 1931; Roy and Smith 1971). Nevertheless, corals
exposed to high turbidity or rapid sedimentation are less diverse and less
abundant than those at reference sites with clear water (Roy and Smith 1971;
Loya 1976a; Randall and Birkeland 1978). Since coral depth distribution is
limited by light penetration, increased turbidity levels may produce an
apparent shift of coral depth distributions toward shallower waters.
Because the relationship of species distributions to light levels is complex
(Sheppard 1982), a simple response to elevated turbidity is unlikely.
Reduced Coral Recruitment—
Unconsolidated substrates are unsuitable for settlement and survival of
some coral recruits (Harrigan 1972 as cited by Johannes 1975). For many
coral species, accumulation of sediment over a hard substrate inhibits
larval settlement and juvenile development (Edmondson 1928; Maragos 1972;
Dodge and Vaisnys 1977).
CASE HISTORIES
A summary of case history data on sedimentation in reef environments is
presented in Table 6. Only those studies containing quantitative estimates
of natural sedimentation rates or anthopogenic Inputs are included in the
table. Qualitative information on sediment loading and response of corals
is discussed later.
Examination of the data in Table 5 reveals that several investigators
have found inverse correlations between sedimentation rates and coral
39
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TABLE 6. CASE HISTORIES OF SEDIMENT IMPACTS ON CORAL REEFS
Location
Sedimentation
Sediment Rates3
Source mg cm"' day"1
Responses or Characteristics
Notes
Reference
St. Thomas, U.S.V.I.
Fringing reefs in several
bays and near small off-
shore islands
Gal eta Island, Panama
Nalu Nega, San Bias Is.
Fringing reefs
Discovery Bay, Jamaica
Lagoon fringing reefs
Guayanilla Bay, Puerto
Rico
Fringing reefs
Barbados, West Indies
W. Coast barrier reef
Negro Bank, Puerto Rico
Fringing reefs
Key Largo, Florida Keys
Patch reef
Puerto R1co
Fouha Bay and YUg Bay,
Guam
Fringing reefs
Kaneohe Bay, Hawaii
Fringing reefs
Airport runway
construction
0.7-5.9
Natural sources 0.3-0.9
Resuspenslon 0.45-1.10
Resuspension by 1.1-9.8
ship traffic
Resuspenslon
1-15
Rivers and re- East Reef
suspension 3.0
West Reef
15.0
Dredging, 37 (6-125)
0.7 km (0.5 ml)
upcurrent from
reef
Engineering
experiment
Rivers and
resuspenslon
Sewage dis-
charge and
watershed urban-
ization
150
6-228
36-41,096
No apparent effects on seagrass, corals,
algae, and fish
No apparent Impact on the coral Montastrea
cavernosa
Coral growth was inversely related to
sediment resuspension rate
10-cm diameter
sediment traps
Measured sediment
accumulation on
dead coral
Rogers (1982)
Lasker (1980)
Dodge et al. (1974)
Aller and Dodge (1974)
Low cover and diversity.of corals related to Preliminary results Morelock et al. (1979)
high resuspension rates
Percent dead coral tissue correlated with
sedimentation rate on outer reef slope
High turbidity and sedimentation resulted in
low cover and diversity of corals
No apparent effects on resistant species of
coral, Siderastrea slderea
No apparent effects on.seven coral species
after 9 day's exposure
Higher species richness, percent cover, and
colony size of corals near bay mouths where
sedimentation was less
Growth rate of corals correlated primarily
with light intensity, not sedimentation rate
Turbidity (FTU)
East Reef 1.5
West Reef 5.5
Minor Impact of
dredging on reef
sedimentation
Ott (1975)
Loya (1976a)
Griffin (1974)
Kolehmainen (1974)
Randall and Birkeland
(1978)
Short-term sediment Maragos (1972)
trapping during
winter storms pro-
duced high sedimen-
tation rates
Sedimentation rates include natural background values where anthopogenic sources are involved.
Limited data available.
-------
community parameters (e.g., species richness, abundance, growth). However,
sedimentation rates from different studies listed in Table 5 can be compared
only in an approximate manner for two reasons. First, variations in the
design and deployment of sediment traps influence the absolute differences
among sedimentation rates reported from different studies (cf. Gardner
1980). Second, the lithology and granulometry of the sediments varied among
the studies.
Natural Sources of Turbidity/Sedimentation
In nature, high turbidity and rapid sedimentation are caused primarily
by nearby river drainage, planktonic production, and resuspension of bottom
sediments. In the following case histories, sedimentation effects were
inferred by correlating coral parameters at various sites with corresponding
values of turbidity or sedimentation.
Fanning Atoll Lagoon--
Roy and Smith (1971) studied the effects of turbidity on coral reef
development in unpolluted Fanning Lagoon which is located in the central
Pacific Ocean about 1,500 km south of Hawaii. The lagoon is characterized
by areas of turbid water, with a calcium carbonate suspended load of 3.5
mg/1, and areas of clear water, where suspended solids averaged about 1.0
mg/1. Depositional rates for these areas were estimated at greater than 1.0
mm/yr and about 0.3 mm/yr, respectively. Because of the shallowness of the
lagoon [mostly 4-15 m (13-49 ft)], illumination at the bottom was always
greater than 5 percent incident light; i.e., well above the minimum light
intensity required for coral growth.
Roy and Smith (1971) concluded that reefs in the clear water were
ecologically different from those in the turbid water. Live corals covered
about 60 percent of the bottom in clear water and about 30 percent of the
bottom in turbid water (Roy and Smith 1971). Ramose corals accounted for 55
percent of the individuals at the turbid site and only 10 percent of those
in the clear-water area. Accordingly, the reef structure in clear water was
massive and steep-sided, while in turbid water it had a gentler slope and
more sediment accumulation. Despite clear ecological differences, species
composition in the two areas was similar with only four species being
excluded from the turbid-water area (Maragos et al., 1970).
41
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Negro-Bank Reefs, Western Puerto Rico—
Loya (1976a) examined two reefs along the west coast of Puerto Rico to
determine the role of turbidity and sedimentation in control of coral
community structure. Coral diversity and living cover were high at the
upper East Reef (H1 = 2.196, cover - 79 percent), where average water
turbidty and sedimentation were low {1.5 FTU and 3.0 mg cm~2 day"1,
respectively). At the West Reef, species diversity and cover were
relatively low (H1 = 1.830, cover = 30 percent), while average turbidity and
sedimentation were much higher (5.5 FTU and 15 mg cm"2 day"1, respectively).
The major source of sedimentation stress appeared to be periodic
resuspension and redeposition of fine sediments after heavy seas.
Relationships between living coral cover, water turbidity, and water depth
for the East and West Reefs are shown in Figure 6.
Species composition and the relative abundance of coral species were
also influenced by sedimentation patterns. A coral community resistant to
sedimentation was identified at the West Reef, with Montastrea cavernosa,
Siderastrea radians, ^. siderea, and Diploria strigosa being the most
successful species. Although Montastrea cavernosa was dominant at both
reefs, M. annularis (the main framework-builder throughout the Caribbean)
was considered abundant only at East Reef.
Fouha and Ylig Bays, Guam-
Randall and Birkeland (1978) studied the effects of sedimentation on
coral reefs of two bays in Guam. In both Fouha Bay and Ylig Bay,
sedimentation was high near the river drainage at the head of the bay and
low at the bay mouth (Table 7). Paralleling this decrease in sediment
loading, the species richness and percent cover of coral communities
generally increased along the shore-to-seaward gradient. Only data for the
most favorable coral habitat (i.e., upper slope) are given 1n Table 6.
Other environmental parameters, including temperature, pH, salinity,
nitrates, and phosphates showed no systematic variation among stations.
Based on their data, Randall and Birkeland (1978) would expect a
"depauperate coral community of less than 10 species covering less than 2
42
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100-
90-
CC
LU 80
8 70
O
Z 60
>
-J 50 H
S 40
DC
ai 30
o.
20-
10-
0
x FTU
• EAST REEF
O WEST REEF
-6.0
-5.0
-4.0
-3.0
2.0
•1.5
g
CO
EC
-T , , ,— I i 1 1 1 1 1 I I r-
8 9 10 11 12 13 14 15 16 17 18 19 20 21
DEPTH (M.)
SOURCE Loya, 1976a
Figure 6. Relationships between percent living coral cover,
turbidity, and water depth, Negro-Bank Reefs,
Puerto Rico.
43
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TABLE 7. CORAL COMMUNITY STRUCTURE AND SEDIMENTATION RATES IN
FOUHA AND YLIG BAYS, GUAM
Coral Community - Upper Reef Slope
Station
FN1
FN2
FN3
FN4
FS1
FS2
FS3
FS4
YN1
YN2
YN3
YN4
YS1
YS2
YS3
YS4
Sedimentation Rate
mg cm'2 day"1
228
100
64.4
6.71
210
133
32.7
33.8
98.5
46.0
22.8
23.9
179
25.0
31.2
18.9
No. of
Species
2
39
116
142
3
40
89
104
3
38
94
127
6
42
85
112
Percent
Cover
0.32
5.23
28.47
25.92
0
16.21
16.12
18.06
0
8.88
17.61
22.13
1.22
7.95
16.83
12.25
Mean
Colony Size
(cm)
8.0
16.5
37.3
31.7
8.9
24.2
24.9
20.2
6.0
20.4
29.0
23.7
28.0
25.9
21.4
19.3
Note: Data are means of average sedimentation rates for eight consecutive
6-wk periods, as measured by tubular collectors approximately 2.4-cm
diameter by 41-cm length. F = Fouha Bay, Y = Ylig Bay, N = north side of
bay, S = south side of bay.
Source: Randall and Birkeland (1978).
44
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percent of the solid substrate" where average sediment loads are about
160-220 mg cm"2 day"1. A "rich coral community of over 100 species covering
over 12 percent of the solid substrate" is expected where average
91
sedimentation rates are about 5-32 mg cnr* day .
Discovery Bay, Jamaica--
Dodge et al. (1974) and Aller and Dodge (1974) studied the growth of
Montastrea annularis coral in relation to sediment resuspension in Discovery
Bay. Both the average growth rate and the maximum growth rate of this
species were inversely proportional to resuspension values (Figure 7).
Resuspension rates in this case were measured by sediment traps placed 50 cm
above the bottom, where the median particle size of resuspended material is
less than 0.062 mm. "Resuspension values" also included fresh deposition,
but Aller and Dodge (1974) showed that newly-deposited material was a minor
component of the sediments collected in their traps.
Anthopogenic Sources of Turbidity/Sedimentation
Several of man's activities elevate turbidty and promote rapid
sedimentation in coral reef environments. Anthopogenic sources include
dredging operations, resuspension of sediments by boat traffic, and
terrestrial runoff associated with urbanization or poor land management.
Several case histories involving these activities are summarized below (also
see Johannes 1975).
Castle Harbor, Bermuda—
Dredging was conducted during 1941-1943 in Castle Harbor, a
semi-enclosed bay along the Bermuda coastline (Dodge and Vaisnys 1977).
Increased sedimentation associated with the dredging operation was
apparently responsible for decreased growth rates in corals. Impacts of
substrate disruption persisted for several years after cessation of
dredging, probably due to periodic resuspension of sediments. Eventually,
all corals older than 20 yr (approximately 10 cm in height) died throughout
the harbor. Population age structures in 1974 (35 yr after dredging)
indicated that corals were still in a phase of high recruitment and
recolonization.
45
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E
LU
rr
|
O
rr
O
X
1.1 •
1.0-
0.9-
0.8-
0.7-
0.6-
c
t 1 B
i
A
+
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1,0 1.1 1.2
- RESUSPENSION (mg/crrWday)
E
0,
LU
rr
|
O
rr
O
LU
0
LU
•fc^.
—
1.1-
1.0-
0.9-
0.8-
0.7-
0.6-
C
T B
•— T ' T
4*
A
+
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
RESUSPENSION (mg/crrWday)
Ranges are given for resuspension values.
Error bars for coral growth rate equal
± two standard deviations.
A.B.C are station names
SOURCE. Aller and Dodge, 1974
Figure 7. Growth rate of coral (Montastre'a annularis) in
relation to sediment resuspension rate, Discovery
Bay, Jamaica.
46
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As a result of the initial impact and extended recolonization period,
dominance in the coral community shifted from Diploria strigosa to
I), labyrinthiformis. Hubbard and Pocock (1972) demonstrated that
ID. labyrinthiformis is more capable of sediment rejection than J). strigosa,
at least for particles larger than fine sand.
Piscadera Bay, Curacao—
Bak (1978) investigated the effects of dredging on a fringing reef
community, 700 m (2,297 ft) from the dredge site. Increased turbidity
during dredging resulted in a reduction of light intensity at 12-13 m (39-43
ft), from initial values of 27-30 percent to less than 1 percent of incident
illumination. Colonies of Porites astreoides. an inefficient sediment
rejector, lost their zooxanthellae and died. Calcification rates of other
corals decreased by about 33 percent. Growth rate impacts appeared to
persist for at least 30-60 days following dredging.
Kaneohe Bay, Hawaii--
Urbanization of the watershed surrounding Kaneohe Bay has resulted in
extensive sediment influx, accounting for an average of about 1 m of
sediment accumulation in the lagoon (Roy 1970; Laws 1981; Hollett and
Moberly 1982). Fine, clay-sized sediments originating from terrestrial
runoff have killed many corals, particularly in the southern basin and on
shallow fringing reefs along the shore (Maragos 1972). The percentage of
the substrate covered by living coral was inversely related to the percent
cover by sediment (Figure 8). However, the relationship is not linear, and
a threshold for development of abundant coral seems to exist at or below
about 20 percent sediment cover. Above this value, most sites have less
than 10 percent coral cover. Hollett and Moberly (1982) concluded that
rapid shoaling of the southern bay was caused primarily by unrecorded
dumping of dredge spoils and accidental spills, not by increased
urbanization and altered land use.
By multivariate analysis of 25 environmental .variables, Maragos (1972)
found that light, salinity, and sewage variables (e.g., phosphate, dissolved
oxygen variation, sediment cover) were the most important factors explaining
47
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80-
£ 6°T
O
o
_l
I 40
O
20-
'• •.
%• •
20 40 60 80
% SEDIMENT COVER
100
Note '• Stations near sewer outfalls not included.
N = 91
SOURCE Maragos, 1972
Figure 8. Coral cover versus sediment cover, Kaneohe Bay,
Hawaii.
48
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differences in growth rates of transplanted corals. Sedimentation rates
accounted for less than 5 percent of the total variation in the growth rate
data. However, sedimentation rates measured by Maragos (1972) were not
representative of average conditions. Sediment traps were deployed for 45
days during a winter period of unusually heavy rain and terrigenous sediment
influx. Coral growth rates were measured over a period of about 20 months.
Other Studies-
Additional case histories indicate a wide variety of coral reef
responses to anthropogenic sediment influx, from essentially no impact
(Griffin 1974; Sheppard 1980b; Dollar and Grigg 1981; Rogers 1982) to
widespread degradation of reef communities (Brock et al., 1965, 1966; Marsh
and Gordon 1974). For example, Griffin (1974) found no effects of dredging
on a nearby coral patch reef in the Florida Keys. The dredge project
resuspended 2,000 kg/day of sediments in the water column, an amount
equivalent to 5 percent of the total baseline load for the entire study
area. Sedimentation rates at the patch reef were not greatly enhanced by
dredging, probably because the reef was located a considerable distance [0.7
km (0.5 mi)] upcurrent from the dredge site. Moreover, the coral patch reef
was initially dominated by Siderastrea siderea. a species considered
tolerant of high sedimentation and low DO (Griffin 1974). In contrast,
turbidity and siltation from dredging operations adversely impacted over
7,000 acres of reef and lagoon near Johnston Island, with coral mortaility
in turbid waters ranging up to 40 percent (Brock et al., 1965, 1966).
49
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SYNTHESIS
Sewage discharges may potentially impact coral reef communities through
several processes:
• Nutrient enrichment
• Sedimentation
• Toxicity.
Adverse effects of sewage discharge on coral reefs have been observed
primarily in poorly-flushed habitats; e.g., enclosed bays or lagoons.
Significant adverse impacts of open ocean discharges have not been
conclusively demonstrated for coral reef communities.
Only two comprehensive studies of sewage disposal into reef
environments have been conducted; one in Kaneohe Bay (Hawaii) and one off
the coast of southern Florida. In the former study, interpretation of
sewage impacts is complicated by other anthropogenic perturbations; e.g.,
dredging and urban runoff (Banner 1974). Moreover, surveys conducted after
sewage diversion from Kaneohe Bay covered an insufficient time for
evaluation of the response of coral communities to decreased sewage inputs
(Smith et a!., 1981). In the other study off the coast of Florida, detailed
results concerning sewage impacts are not yet available.
The following sections provide a synthesis of information on the
impacts of sewage discharges on coral reef communities. Potential impacts
are discussed in relation to the underlying mechanisms responsible for
ecological change: nutrient enrichment, sedimentation, and toxicity. Data
from case histories reviewed in previous chapters are integrated below to
produce an overall assessment of sewage discharge effects.
50
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NUTRIENT ENRICHMENT
Nutrient enrichment of coral reef communities produces a variety of
direct and indirect effects. At low levels of nutrient input, primary
production of benthic algae is enhanced without affecting biomass, species
composition, or trophic structure (Kinsey and Domm 1974). Moderate levels
of enrichment cause increased primary production and biomass in both
phytoplankton and benthic algal populations (Laws and Redalje 1979; Smith et
al., 1981). With increasing nutrient inputs, shifts in species dominance
often lead to blooms of nuisance algae, especially planktonic flagellates
(Clutter 1972; Mahoney and Mclaughlin 1977) and benthic green or blue-green
algae (Banner 1974; Snedaker, 24 August 1982, personal communication).
Blooms of green algae (Ulva, Enteromorpha) and filamentous blue-greens have
been observed near sewage outfalls on coral reefs in the Red Sea and in
south Florida, respectively (Walker and Ormond 1982; Snedaker, 24 August
1982, personal communication). Some opportunistic algae are extremely
sensitive to nutrient enrichment. For example, in Kaneohe Bay the green
algae (Dictyosphaeria cavernosa) responded to sewage inputs at distances of
over 10 km (6.2 mi) from the outfalls (e.g., Banner 1974). Enhanced plant
growth and sewage particles around outfalls often attract fishes (Johannes
1975). However, algal blooms may persist even in the presence of enhanced
grazer populations (Walker and Ormond 1982).
In addition to its direct effects on production and biomass of algae,
moderate nutrient enrichment may lead to the following impacts:
• Enhanced bacterial populations may kill coral tissue
(Mitchell and Chet 1975).
• Benthic algae may colonize coral skeletons, overgrow living
corals, and form thick mats which kill all underlying
organisms by blocking light and trapping sediment (Maragos
and Chave 1973; Banner 1974; Walker and Ormond 1982).
t Elevated phytoplankton populations may reduce light
penetration, which probably affects coral nutrition, growth,
and survival through impacts on zooxanthellae (Smith et al.,
1981).
51
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t Increased water-column production may favor enhanced growth
of benthic filter-feeders (e.g., sponges, bryozoans,
tunicates), which outcompete corals for space (Maragos 1972;
Birkeland 1977; Smith et al., 1981; Brock and Smith 1983).
t Opportunistic coral species such as Stylophora pistillata
may dominate or replace other corals (Loya 1976c; Walker and
Ormond 1982).
• Heterotrophic processes may overwhelm autotrophic production
and calcification, leading to net erosion of reefs (Kinsey
1979).
The relative importance of the above mechanisms in controlling coral reef
response to sewage inputs may vary among reef types and geographic regions.
Unfortunately, the available data are insufficient to relate reef structure
and species composition to response mechanisms.
Aside from the previously described impacts attributable to moderate
levels of enrichment, extremely high nutrient inputs exert additional stress
by promoting sedimentation and toxicity. High nutrient loading enhances
planktonic primary production, which leads to increased sedimentation of
organic material, e.g., in Kaneohe Bay (Smith et al., 1981). High phosphate
levels also inhibit calcification by corals and coralline algae (Kinsey and
Davies 1979).
The responses of coral communities to natural variations in nutrient
loading provide interesting comparisons with enrichment effects due to
sewage discharge. Birkeland (1977) described the effects of natural
nutrient inputs by upwelling on coral reef communities off the Pacific coast
of Panama. With a rich supply of nutrients, fouling organisms such as
filamentous algae, bryozoans, and tunicates rapidly colonize open substrate
and overgrow most coral recruits. As nutrient (and light) levels decrease,
the rate of biomass accumulation on benthic substrates declines, and
hermatypic corals have a better chance of reaching a size large enough to
avoid being overgrown. Thus, r-selected fouling species dominate the later
stages of reef succession in upwelling regions of the eastern Pacific. By
52
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contrast, k-selected coral species dominate "climax" communities of the
nutrient-poor Caribbean.
Moderate sewage inputs may mimic nutrient enrichment by natural
upwelling. The parallels between sewage-modified communities and those of
upwelling areas described by Birkeland (1977) are striking; e.g., rapid
growth of benthic organisms, high biomass of filamentous algae, low
diversity of corals, and domination by benthic filter-feeders.
The effects of sewage will vary with reef trophic status, which is
often related to biogeographic differences. In nutrient-poor regions (e.g.,
central Pacific and Caribbean reefs), anthropogenic nutrient inputs may
cause profound shifts in community structure; i.e., from domination by
corals towards increased importance of r-selected filter-feeders. In
upwelling areas (e.g., eastern-Pacific Panamanian reefs), moderate sewage
inputs are less likely to cause dramatic changes since reef biota are
already adapted to nutrient perturbations. Nonetheless, phosphate toxicity
(Kinsey and Davies 1979) may play a role in determining reef calcification
rates in upwelling areas.
SEDIMENTATION
Suspended solids in receiving waters for sewage discharges originate
from three sources: particles contained in effluents, particulate organic
matter produced by nutrient enrichment, and natural seston. The relative
importance of these sources depends on wastewater treatment level.
Little information is available on the direct effects of sewage solids
on hermatypic corals. In most sewage discharge studies (e.g., Russo et al.,
1979; Smith et al., 1981; Walker and Ormond 1982), solids deposition
appeared to be less important to coral reef status than nutrient enrichment.
However, the case histories examined generally involved low mass emissions
of sewage solids (e.g., secondary treatment at Kaneohe Wastewater Treatment
Plant) or efficient dispersal of effluents (Mokapu Point outfall).
High turbidity and rapid sedimentation originate from sources other
than sewage discharge (e.g., dredging, sediment resuspension, terrestrial
runoff). Laboratory and field studies have indicated the following adverse
impacts of suspended or deposited particles on corals:
53
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• Death caused by burial (Edmondson 1928; Marshall and Orr
1931)
• Growth inhibition due to reduced light availability and
additional energy expenditure for sediment rejection
(Maragos 1972; Dodge et al., 1974; Bak 1978; Dallmeyer et
al., 1982)
• Reduced coral abundance and species richness (Roy and Smith
1971; Loya 1976a; Randall and Birkeland 1978)
• Failure of coral recruitment (Maragos 1972; Dodge and
Vaisnys 1977).
Few studies have examined long-term impacts of anthropogenic sedimentation
on coral communities (e.g., Dodge and Vaisnys 1977).
Despite the potential for adverse effects, most corals are capable of
clearing a certain amount of sediment from the surface of the colony. An
efficient sediment-rejector like Montastrea cavernosa is capable of cleaning
itself at deposition rates up to about 14 mg cm~2 day'1 (Lasker 1980).
Average sedimentation rates measured over extended periods (e.g., weeks,
months) in natural coral reef habitats of the Caribbean zone range from 0.3
to 37 mg cnr2 day"1 (Griffin 1974; Ott 1975; Loya 1976a; Lasker 1980; Rogers
1982). In the Indo-Pacific region, corresponding sedimentation values range
from 0.1 to 228 mg cm'2 day"1 (Marshall and Orr 1931; Smith and Jokiel 1975;
Schuhmacher 1977; Randall and Birkeland 1978). At sediment deposition rates
greater than 10-15 mg cm'2 day'1, coral communities exhibit apparent
modifications in response to sedimentation (or turbidity) stress; e.g.,
appearance of sediment-resistant species, reduced abundance and diversity,
predominance of branching growth forms.
Although quantitative data are limited, relationships between coral
response parameters and sedimentation rate have been inferred by many
researchers (e.g., Dodge et al., 1974; Loya 1976a; Randall and Birkeland
1978). Response curves based on data from Randall and Birkeland (1978) are
presented here to illustrate the functional dependence of coral community
structure on the rate of sediment deposition (Figures 9, 10, 11, and 12).
54
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CO
UJ
O
UJ
a.
CO
a:
O
o
200 i
100 •
90-
80'
70-
60-
50-
40-
20-
10'
9
8
7
6
5 •
4 -
3 •
2 -
In Y = 4.97 - 0.018X
r2 = 0.77, P<0.05
\
\
\
\
\
\
95% CONFIDENCE LIMITS \
50
100 150 200 250
SEDIMENTATION RATE (mg cm"2 day1)
SOURCE Data from Randall and Birkeland, 1976
Figure 9. Coral species richness as & function of sedimentation
rate, Guam.
55
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DC
LLJ
o
O
o
o
UJ
g
UJ
£L
100 •
90 •
80 •
70 •
60-
50 •
40-
30 -
20 -
10 •
9'
8'
7 •
6 •
5-
4 -
3 -
2 -
In Y = 3.17 - 0.013X
.r2 = 0.64, P < 0.05
95% CONFIDENCE LIMITS
50 100 150 200 250
SEDIMENTATION RATE (mg cnr* day1)
SOURCE. Data from Randall and Birkeland, 1978
Figure 10. Coral percent cover as a function of sedimentation
rate, Guam.
56
-------
LU
N
CO
O
O
cc
O
O
LLI
100-;
90-
80-
70^
60-
50-
40
30
20
10
9
6
7 •
6'
5
4 -
3-
2-
In Y = 3.29-0.0041X
r2 = 0.34, P < 0.05
95% CONFIDENCE LIMITS
50
100
150
200
250
SEDIMENTATION RATE (mg cnr* day1)
SOURCE Data from Randall and Birkeland, 1978
Figure 11. Coral colony size as a function of sedimentation
rate, Guam.
57
-------
140
120-
100-
co
UJ
O
UJ
a
to 80
_i
cc
8
O
i
60-
40-
20-
In Y = 6.06 + 4.79X
rz = 0.84, P < 0.05
95% CONFIDENCE LIMITS
10 15 20 25 30
PERCENT COVER OF CORALS
SOURCE. Data from Randall and Birkeland, 1978
Figure 12. Coral species richness as a function of coral
cover, Guam.
58
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Only the data from the upper slope communities were used to develop the
curves in Figures 9 to 12. Because the upper slope communities form the
best-developed reefs and are normally subject to the least sedimentation
relative to other coral habitats, they should reveal the clearest responses
to gradation of sediment influx. Lines were fitted to the data in Table 6
by using least-squares linear regression. Species richness, percent cover,
and mean colony size of corals are each inversely related to sedimentation
rate. Coral species richness is positively correlated with percent cover
(r2 = 0.75; p < 0.05), indicating that no single species is a clear
competitive dominant (Porter 1974). In general, the response of coral
communities in other reef zones to sediment inputs is similar to the
responses illustrated here.
The variability of coral community parameters (species richness,
percent cover, and mean colony size) changes along the gradient of
sedimentation rates shown in Figures 9, 10, and 11. At sedimentation values
less than 40-50 mg cm"2 day"1, the variance around the regression lines is
relatively low. Since many corals of the upper reef slope flourish only
where sedimentation is minimal, the low variability of species number and
percent cover at sedimentation rates less than 40-50 mg cm" day" may
reflect the control of community structure through biological mechanisms
such as competition, predation, and mutualism. At the highest sedimentation
rates (150-250 mg cm"1 day"1), the low variance in community structure is a
reflection of environmental stress. Only a few resistant species are able
to survive the extreme sediment influx, and community structure is directly
controlled by physical variables rather than biological interactions. In
the midrange of sedimentation values, both physical and biological
mechanisms may be important in determining community structure, with
moderate stress producing a number of alternative community structures.
Thus, the variance in community structure is greatest at the midrange of
sediment stress (50-150 mg cm'2 day1). Although the data obtained from
Randall and Birkeland (1978) may be too variable for precise prediction of
coral reef impacts following changes in the sedimentation regime, they
nonetheless serve to illustrate the type of data required for development of
quantitative response models.
Based on information from Randall and Birkeland (1978) and other case
histories reviewed previously, an impact scale was developed for various
levels of sediment deposition (Table 8). Individual coral communities were
59
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TABLE 8. ESTIMATED DEGREE OF IMPACT ON CORAL COMMUNITY CAUSED
BY VARIOUS LEVELS OF SEDIMENTATION - SUMMARY
Sedimentation Rate
mg cm"2 day"1
Estimated Impact
1-10
10-50
> 50
SLIGHT TO MODERATE:
Decreased abundance/cover
Altered growth forms
Decreased growth rates
Possible reductions In recruitment
Possible reductions in numbers of species
MODERATE TO SEVERE:
Greatly decreased abundance/cover
Greatly decreased growth rates
Predominance of altered growth forms
Reduced recruitment
Decreased numbers of species
Possible invasions of opportunistic species
(e.g., algae)
SEVERE TO CATASTROPHIC:
Severe degradation of communities
Most species excluded
Many to most colonies die
Recruitment severely reduced
Regeneration slowed or stopped
Invasion of open substrates by opportunists
Coral cover severely reduced
60
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rated according to their response to sedimentation (i.e., slight to
moderate, moderate to severe, etc.) and the corresponding range of
sedimentation rates was recorded under the appropriate response category
(Table 9). The levels of sedimentation listed in Table 8 represent a
summary of the case history data compiled in Tables 3 and 9. Because of the
limited data available, the degree of impact for each level of sediment
deposition should be considered tentative.
A preliminary assessment of sedimentation impacts associated with
sewage discharges has been conducted as part of the technical review process
for Section 301(h) (Clean Water Act) applications received during 1979.
Maximum predicted deposition rates for sewage outfalls located in Hawaii and
Puerto Rico (regions with coral reefs) are summarized in Table 10. It
should be emphasized that the deposition rates in Table 10 are "worst-case"
estimates for sewage solids accumulation; i.e., they do not incorporate
resuspension and transport of sediment particles by waves and currents.
However, they also do not include the effects of toxic substances in sewage
and ambient sediment influx. None of the proposed outfalls will discharge
directly to a coral reef habitat. Despite these limitations, it is
interesting to compare the sediment deposition rates predicted for these
sewage discharges (Table 10) with the ranges of sedimentation rates derived
for various levels of impact (Table 8). All of the sediment deposition
rates calculated for the proposed sewage discharges are extremely low
compared to natural sedimentation rates found on most coral reefs.
TOXICITY
Toxic effects on corals and other reef organisms may result from one or
more of the chemicals commonly found in sewage effluent: metals, chlorine,
phosphate, pesticides, and petroleum hydrocarbons. Concentrations of these
chemicals vary greatly among discharges and through time for a specific
discharge. Because a multitude of toxic substances may occur in sewage
effluent, additive and synergistic effects of pollutants are important.
Aside from the effects of petroleum hydrocarbons, toxic effects on corals
and other reef organisms have received little attention.
The effects of free residual chlorine on reef organisms were reviewed
by Johannes (1975). He cites several studies which indicate that reef
61
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TABLE 9. ESTIMATED DEGREE OF IMPACT ON CORAL COMMUNITY
CAUSED BY VARIOUS LEVELS OF SEDIMENTATION
Estimated Impact'
Sedimentation Bate
mg cm" day"
Reference
SIight to moderate
Moderate to severe
Severe to catastrophic
6-20
3
7-8
^1
1-15
20-50
15
14
37 (6-125)
10
>50
Randall and Birkeland (1978)
Loya (1976a)
Lasker (1980)
Dodge et al. (1974)
Ott (1975)
Randall and Birkeland (1978)
Loya (1976a)
Lasker (1980)
Griffin (1974)
Morelock et al. (1979)
Randall and Birkeland (1978)
Categories correspond to impact levels identified in Table 8
-------
TABLE 10. WORST CASE ESTIMATES OF SOLIDS DEPOSITION RATES FOR
SEWAGE OUTFALLS NEAR CORAL REEFS3
Average Sedimentation Rate
Outfall Location mg cm"2 day"
Honouliuli, HI 0.036
Sand Island, HI 0.029C
Kailua-Kaneohe, HI 0.056
-------
fishes are sensitive to chlorine. Davis (1971 as cited by Johannes 1975)
tested the effects of 0.49 mg/1 chlorine on the planulae of three species of
Hawaiian corals and found that exposure for up to 7 hours was not lethal.
Adult corals were not tested.
Phosphate pollution has been implicated as a factor contributing to the
decline of reef ecosystems in Eilat, Red Sea (Fishe!son 1973; Loya 1975,
1976b; Fishelson 1977). However, chronic oil pollution may account for
most, if not all, of the pollution damage observed on the Eilat reef flat
(Rinkevich and Loya 1977; Loya and Rivkevich 1979). Effects of elevated
phosphorus levels should not be dismissed, however. Kinsey and Davies
(1979) experimentally enriched a patch reef at One Tree Island, Great
Barrier Reef, with phosphate (2 uM) and nitrogen (20 uM urea plus ammonia)
for 3 hours each day at low tide over a period of 8 months. They found that
reef calcification was reduced by at least 50 percent, and attributed this
supression to phosphate enrichment.
Reimold (1975) sampled coastal biota from Puerto Rico and the Virgin
Islands to determine tissue levels of chlorinated hydrocarbons (dieldrin,
DDT, DDE, TDE, PCBs) and mercury. Body burdens of these pollutants were
detected at low levels in reef fishes and invertebrates at one or more of
the 15 survey sites. Olafson (1978) surveyed organochlorine pesticide body
burdens in two species of fish, two species of corals, and one species of
bivalve mollusc from the Great Barrier Reef. Lindane was the only
organochloride consistently detected, and tissue levels were very low. Both
authors hypothesized that land-use practices were a major factor affecting
the distributions of toxic substances in the biota.
Neither Reimold (1975) nor Olafson (1978) assessed the effects of toxic
residues in reef organisms. To date, only the study of McCloskey and
Chesher (1971) has examined the effects of chlorinated hydrocarbons on coral
colonies. McCloskey and Chesher (1971) subjected the corals Montastrea
annularis, Acropora cervicornis, and Madracis mirabill's to mixtures of
p, p'-DDT, dieldrin, and Aroclor 1254 (a PCB) in equal proportions.
Colonies were dosed with 10, 100, and 1,000 ppb of each of the three
compounds. No changes in feeding behavior, polyp extension, sediment
clearing, settling of coral associates, or crystal formation were observed.
However, the authors recorded an increase in respiration (R) and a decrease
64
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in photosynthesis for all three species, such that the P/R ratio fell below
1.0. Photosynthesis remained depressed for up to 4 days, at which time the
experiment was terminated.
Although petroleum hydrocarbons are not usually present at high
concentrations in sewage effluents, chronic exposure of reef organisms to
low concentrations of these toxicants is a potential problem. Loya and
Rinkevich (1980) thoroughly reviewed the effects of oil pollution on reef
communities and documented a multitude of detrimental impacts, many of which
exhibited delayed response. Researchers have documented decreased viability
of coral colonies (Eisler 1975; Loya 1975, 1976b; Rinkevich and Loya 1977,
1979; Peters et al., 1981), decreased growth rates {Birkeland et al., 1976),
damage to cells and tissues (Birkeland et al., 1976; Peters et al., 1981),
altered behavior (Eisler 1975; Reimer 1975a, 1975b; Cohen et al., 1977; Loya
and Rinkevich 1979), and excessive production of mucous with a rich
bacterial flora (Mitchell and Chet 1975; Ducklow and Mitchell 1979).
Elevated bacterial populations were implicated as contributors to coral
demise (Mitchell and Chet 1975; Ducklow and Mitchell 1979). Loya and
Rinkevich (1980) also documented effects of oil pollution on the
reproduction and recruitment of corals. Observed effects included reduced
colonization by corals in areas subjected to chronic oil pollution (Loya
1975, 1976b; Rickevich and Loya 1977), deleterious effects on the
reproduction systems of corals (Loya 1975; Rinkevich and Loya 1977, 1979;
Peters et al., 1981), and premature release of coral planulae upon contact
with petroleum compounds (Cohen et al., 1977; Loya and Rinkevich 1977,
1979). Loya and Rinkevich (1979) speculated that premature release of
planulae results in reduced survival and settlement, especially if the
receiving environment is contaminated with hydrocarbons.
In addition to toxic substances in the sewage effluent, toxic
substances associated with enriched bottom sediments may also have an
important influence on coral reef communities near sewage outfalls.
Hydrogen sulfide in bottom sediments increases with proximity to sewage
discharge sites (Sorokin 1973c). The release of toxic sulfides from bottom
sediments in southern Kaneohe Bay may have been responsible for coral
mortality and the low diversity of reef communities (Maragos 1972, Maragos
and Chave 1973). In some instances, resuspension of sediments during storms
might also result in a transfer of toxic materials (e.g., PCBs, metals,
65
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pesticides) into the water column, increasing the likelihood of biological
contamination.
Past studies have addressed only the short-term effects of toxic
substances on coral reef organisms. Yet results of several studies of
petroleum contamination suggest that sublethal and lethal effects may, in
some cases, be delayed or prolonged. Although uptake of petroleum
hydrocarbons by corals occurs relatively quickly, depuration does not.
Peters et al. (1981) and Knap et al. (1982) reported that depuration of
corals did not occur within 2 weeks after cessation of exposure. Death of
coral tissue following short-term exposure to Bunker C oil may not occur
until 2 weeks after exposure (Birkeland et al., 1976). The persistance of
delayed toxic effects and the severity of those delayed effects have yet to
be established for coral reef systems.
66
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CONCLUSION
The response of coral reef communities to sewage effluent components,
including nutrients, suspended solids, and toxic substances may vary from
reef to reef depending on the specific reef biota and biogeographic zone.
Spatial and temporal variations in the response of coral reefs to sewage
inputs and the mechanisms underlying these responses are not fully
understood. Available information indicates, however, that most coral
species can tolerate limited amounts of nutrient enrichment and
sedimentation rates. Within the range of environmental variation observed
in nature, coral reef communities exhibit dramatic shifts in structure and
function along gradients in nutrient influx (e.g., from oligotrophic seas to
eutrophic upwelling areas) and sedimentation rates (e.g., from inner bays
and lagoons to offshore reef slopes).
Stimulation of marine productivity by slight nutrient enrichment may be
viewed as a potential benefit, but possible subtle changes in reef ecology
due to moderate sewage inputs may have chronic or long-term impacts on these
distinctive habitats of limited distribution. Alterations of coral-reef
community composition, diversity, and abundance caused by moderate sewage
inputs are similar to natural variations of reef communities along
environmental gradients. However, high nutrient inputs from sewage
discharges are potentially harmful to coral reef communities. Although most
coral species can tolerate limited eutrophication and sedimentation, the
cumulative impacts of a large discharge in poorly-flushed waters may lead to
disruption of coral community structure and eventual erosion of the reef
through mechanical, chemical, and biological processes. Climax species of
corals, i.e., slow growing, slow reproducing, K-selected forms, may be more
sensitive to sediments and toxic chemicals contained in sewage effluents
than pioneering (r-selected) species. Moreover, high nutrient inputs may
enhance the growth of pioneering species causing a shift in species
composition eventually, leading to the replacement of corals by other
benthic species (e.g., bryozoans, tunicates, and filamentous algae).
67
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Available data suggest that observed impacts of nutrient enrichment in
coral reef habitats are greater than impacts of sewage-solids deposition.
Maximum predicted sedimentation rates near open-coast outfalls discharging
primary-treated effluent are one to two orders of magnitude lower than
natural sedimentation rates on biologically-rich coral reefs (e.g.,
0.001-0.056 mg cm~2 day"1 for sewage solids vs. 1-10 mg cm~2 day'1 for
natural sedimentation).
Despite the large amount of information available on the basic ecology
of coral reefs, current data on anthropogenic impacts are limited. Although
specific information is available for certain localities, at present, data
gaps exist in the following key areas of concern:
• Effects of toxic chemicals in sewage effluents
• Importance of toxicity, nutrient enrichment, sedimentation,
and oxygen depression as a function of sewage loading and
flushing potential
• Synergistic and additive effects of various components in
sewage effluents
t Recovery times from sewage impacts.
68
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APPENDIX: LITERATURE SEARCH AND INFORMATION SOURCES
An extensive file of information on coral reef ecology and impacts of
sewage was already on hand in the Tetra Tech library. This file was updated
in three ways:
t Computerized search of biological information
• Manual library search
• Personal contacts with recognized experts on coral reef
ecology.
COMPUTERIZED SEARCH
A computerized search for literature on pollution of coral reefs was
conducted by CERL (U.S. EPA, Corvallis, OR) during March, 1982. The
following data bases were accessed: BIOSIS, TOXLINE, NTIS, and WRA. From
computer printouts of references, Henry Lee and Mark Schaefer of CERL
compiled a "Bibliography of Publications related to the Effects of Sewage
Discharges on Coral Reefs (July, 1982). This bibliography, composed of 114
references, was made available to Tetra Tech.
MANUAL LIBRARY SEARCH
A manual search of recent journal and abstract issues was conducted
from August 12, 1982, through December 1, 1982, using the library facilities
of the University of Washington. In general, journal issues for the years
1981 and 1982 were examined. Earlier issues were examined only for high
priority items, some of which are not published annually (e.g., Proc. Int.
Coral Reef Symp.). The search included the following journals.
Adv. Ecol. Res.
Amer. Natur.
69
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Aquat. Bot.
Austr. J. Mar. Freshwat. Res.
Biol. Bull.
Biol. Conserv.
Biol. Geol. of Coral Reefs
Biol. Oceanogr.
Bull. Mar. Sci.
Coral Reefs
Ecology
Environ. Conserv.
Environ. Pollut.
Est. Coast!. Mar. Sci.
Est. Coastl. Shelf Sci.
J. Conseil Explor. Her
J. Exp. Mar. Biol. Ecol.
J. Mar. Res.'
Limnol. Oceanogr.
Mar. Biol.
Mar. Ecol. Prog. Ser.
Mar. Environ. Res.
Mar. Pollut. Bull.
N. Zealand J. Mar. Freshwat. Res.
Oceanogr. Acta
Oecologia
Oikos
Pac. Sci.
Proc. Int. Coral Reef Symp.
Science
Water Air Soil Pollut.
In addition, the following reference sources were consulted:
Aq. Sci. Fish. Abstr. 1982 12(1-3)
Biol. Abstr. 1982 74(1-8)
Current Contents 1982 June 7-October 18
Oceanic Abstr. 1982 19(1-3)
1981 18(1-6)
70
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PERSONAL CONTACTS
Personal contacts with recognized experts on coral reef ecology were
made largely by phone and/or letter. The following individuals were
contacted:
Name
Dr. C.
Dr. D.
Dr. S.
Dr. C.
Dr. T.
Dr. E.
Dr. J.
Dr. G.
Dr. R.
Dr. W.
Dr. R.
Dr. P.
Dr. D.
Dr. A.
Dr. J.
Dr. H.
Dr. J.
Dr. V.
Dr. E.
Dr. R.
Dr. C.
Dr. E.
Dr. T.
Dr. S.
Dr. S.
Dr. T.
Dr. F.
Dr. R.
Birkeland
Cheney
Coles
Cutress
Duke
Gomez
Gonzales
Griffin
Highsmith
Jaap
Johannes
Jokiel
Ki nsey
Kohn
Kumagai
Lasker
Maragos
McFarland
Powel1
Randall
Rogers
Shinn
Sleeter
Smith
Snedaker
Suchanek
Talbot
Tsuda
Affiliation
Univ. Guam Marine Lab., Guam
Shapiro and Associates, Seattle, WA
Hawaiian Electric Co., Honolulu, HI
Univ. Puerto Rico, Mayaguez, PR
U.S. EPA, Gulf Breeze, FL
Univ. Philippines, Quezon City, Philippines
Univ. Puerto Rico, Mayaguez, PR
Univ. Florida, Gainesville, FL
Friday Harbor Lab., San Juan Is., WA
Florida Dept. Natural Resources, St. Petersburg, FL
CSIRO, W. Australia
Hawaii Institute Marine Biology, Kaneohe, HI
Univ. Georgia, Athens, GA
Univ. Washington, Seattle, WA
M & E Pacific, Inc., Honolulu, HI
State Univ. New York, Buffalo, NY
U.S. Army Corps of Engineers, Kaneohe, HI
Waterways Experiment Station, Vicksburg, MS
Texas A & M Univ., College Station, TX
Univ. Guam Marine Lab., Guam
W. Indies Lab., Farleigh, Dickinson Univ., USVI
U.S. Geological Survey, Miami Beach, FL
Bermuda Biological Station Research, Bermuda
Hawaii Institute Marine Biology, Kaneohe, HI
Univ. Miami, Miami, FL
West Indies Lab., Farleigh Dickinson Univ., USVI
California Academy Science, San Francisco, CA
Univ. Guam Marine Lab., Guam
71
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REFERENCES
Aller, R.C., and R.E. Dodge. 1974. Animal-sediment relations in a tropical
lagoon - Discovery Bay, Jamaica. J. Mar. Res. 32:209-232.
Amesbury, S.S., R.T. Tsuda, R.H. Randall, C.E. Birkeland, and F.A. Gushing.
1976. Limited current and underwater biological survey of the Donitsch
Island sewer outfall site, Yap, Western Caroline Islands. Tech. Rep. No.
24, University of Guam Marine Laboratory.
Anderson, G.R.V., A.H. Ehrlich, P.R. Ehrlich, J.D. Roughgarden, B.C.
Russell, and F.H. Talbot. 1981. The community structure of coral reef
fishes. Amer. Natur. 117:476-495.
Ayal, Y., and U.N. Safriel. 1982. Species diversity of the coral reef - a
note on the role of predation and of adjacent habitats. Bull. Mar. Sci.
32:787-790.
Bak, R.P.M. 1978. Lethal and sublethal effects of dredging on reef corals.
Mar. Pollut. Bull. 9:14-16.
Bak, R.P.M., and J.H.B.W. Elgershuizen. 1976. Patterns of oil-sediment
rejection in corals. Mar. Biol. 37:105-113.
Bak, R.P.M., R.M. Termaat, and R. Dekker. 1982. Complexity of coral
interactions: Influence of time, location of interaction and epifauna.
Mar. Biol. 69:215-222.
Bakus, G.J. 1969. Energetics and feeding in shallow marine waters. Int.
Rev. Gen. Exp. Zoo!. 4:275-369.
Bakus, G.J. 1972. Effects of the feeding habits of coral reef fishes on
the benthic biota. Proc. Int. Symp. Corals and Coral Reefs (1969). J. Mar.
Biol. Assoc. India 1972:445-448.
Banner, A.H. 1968. A fresh-water "kill" on the coral reefs of Hawaii.
Tech. Rep. No. 15, Hawaii Institute of Marine Biology, University of Hawaii,
Honolulu, HI. 29 pp.
Banner, A.H. 1974. Kaneohe Bay, Hawaii: Urban pollution and a coral reef
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