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and mich less a Islas Naranjos mad Isla Margarita (19). Moreover, similar differences occurred over just a few hundred meters between shores directly aposed to ar shclered from the wind-driven oil (201. On an cven smaller scal, extreme low rides between 10 and 19 May (6, 21) caused oil to carmulate along the seaward borders of reef flats, whereas just shoreward much less oil contacted the substratum. In general, intercidal babicas just above mean low water were the most heavily oiled, including mangrove roots and sedi

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Fig. 2 Region of the Republic of Pa affected by the 27 April 1986 oil spill, shown as increasing cadangoscens (A o C). (A) Location within Panama, just cast of the Canbbean carance to the Panama Canal. (B) The boxed area includes the most heavily one coastal habitats. Punta Galeta, insick the boxed area is 924N, 79°52'W. Lightly oiled and unoiled study sates are cast of Bahia bas Minas, car Portobelo and Isla Grande. (C) Detail of the most heavily oiled ara and location of study sites. Encircled "R" on Isla Pavardi marts the refinery wtore the oil spill occurred. Horizontal hacching denotes ambarmemes where like all penetrated. Symbols for types of study sites (open symboks, worked as highly oiled sites, filled symbols, osled sites): 4, mangrove root, scara bed; O, subtidal coral reef, data collected only after the oil pit: , suboidal coral reef, data collected both before and after the oil spilt the four sites near Portobelo and Isla Grande were not oiled, the site a Isla Margria was moderately oiled, and the site at Punta Galet was heavily oiled; , roffa somatopods; mulcirayed star, reef flat communicy, Punia Galleta, s-payed symbol, mangrove forest.

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Fig. 3. Organisms and habitus faced by the
April 1986 oil spill a Bahia Las Mines, Press
(all photographs by C. Hansen ccepe (D) by S.
D. Garty). (A) Oi accumulated stong dacia
ward edge of the Galeta reef far a bow ticke (soen
as the dark border in the cover photo), directly
coating and killing plants and animals, including
the zoanchid Pelyhos sp. (higher perd in fore
ground) and the hydrocoral Millo
ing through oil in background). (B) A
od accumulated along sand beaches,
soaked into the sand and scaded on the shore
ward recf flat a low ride, killing scagrana, algas
and invertebrates. The rectangular objects in the
foreground are polyurethane matures wed by
cleanup crews to absorb oil. (C) Underwater vica
of the coral S. sideve partially killed by all (hori
zontal length in the photographe, 12 cm). Live
tissue forms the dark roddish aa a the bottom.
The central, ligta-colored area is seen showing
through partially dead issue, which is to being
colonized by algae. The her araa dhe top is
bare skeleton Covered by a film of
Oil-covered intercidal surfaces of
red mangrove, R.mk, bilingon
spibiota on the roots. Reticved on the wei
their leaves, defoliatod branches ladd
lifting the roots out of the water and thus bling
subroidal cpibiota thar previously csopod dirca
contact with floating oil. (E) Dead magon
treo form a band about 8 to 100 m wide
(February 1987), making the area where all
accumulated as it catered the mangrove forces
(horizontal distances: foreground -0.4 km and
background -1.3 km). A band of deftiated trees
was apparent within 2 months after the spill and
widened charcaftar.

6 JANUARY 1989

ARTICLES 39

Riverine

70

Live

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Dead

NS

ments, reef-flat seagrass beds, coral rock, and beaches. In contrast, sis of aromacic hydrocarbon fractions (22). Preliminary results higher than normal seas after the Witwater spill caused heaviest oiling generally parallel dassificacion of sites based on visual inspection, as in high inceridal and supercidal habitats, with much more transport shown here for the concentracion of saturated hydrocarbons in of oil into mangroves far from shore (4). Much less oil was observed tissues of the coral Siderastrea sidera (Table 1). subridally.

In addition to these qualitative observations, samples of water, substrata, and organisms were collected for analysis of hydrocarbon Biological Effects by means of gas chromatography and ultraviolet fluorescence analy.

Consequences of the spill were assessed differendy, depending on

the types of data available from before the oil spill (23). Ideall, Channel Open

biological parameters should have been measured & oiled and

unoiled sites before and after the spill. This condition was satisfied Live

Leaty
Myrtitopsis Crassostrea

algas

for biota of mangrove roots and suboidal corals. Extensive prespill
data are available for the reef flat at Galeta, but there are no control
sites and effects must be inferred from cemporal change and from the
spacial distribution of oiling on the reef Alar. In contrast, there are
little or no appropriate prespill data for suboidal scagrass communi-
ties. In this cascs, comparisons were made between oiled and unoiled

sites after the spill, confounding the treatment (oiling) and geogra.
Doad
Mytilopsis
Crassostrea

phy (Bahia las Minas verus the region between Portobelo and Isla
Grande) (Fig. 2). The value of this approach is strengthened by
information suggesting that faunas in seagrass beds were similar in
the two regions before the spill (24), but confidence in assessment of
oiling effects in this habitar is still more limited than in other habitats

studied. olepole

Mangrove communities. Red mangrove, Rhizophora mangle, forms Sessile animals

nearly all of the fringing forest along this coast (17). By September 1986, a band of dead or dying trees marked the zone where oil washed ashore between Punta Galeta and Islas Naranjos (Fig. 3); no such band appears in photographs taken just as the oil was coming ashore. By November 1987 dead mangroves occurred along an estimated 27 km of the coast (25). Seedlings transplanted to heavik: oiled sites did not produce new leaves, in contrast to transplants ar an unoiled site (20).

The prop roots of R. mangle are overgrown by algae and invertebrates that vary in species composition with exposure to che sca (Fig. 3) (6, 27). The epibiota on roots in three different habitats were sampled before and after the spill (Fig. 2) (28). Before the spill (Fig. 4), roots of trees directly facing the open occan were covered with foliose algac and sessile invertebrates such as sponges, hy.

droids, and ascidians. In mangrove channels, the edible oyster, Fig. 4. Percent cover of formerly abundant taxa and oil on mangrove roots in Crassostrea rhizophorae, and a barnacle, Balanus improvisus, were most nivcrine, channel, and open coast habitats before and after the oil spill. Q, abundant on roots. Roots in small rivers were dominated by the Prespill data; O, unoiled sites; and, oiled sites. Means are plotted = 1 SE, converted from arcsinc transformations. Some crror bars lic within the

false mussel Mytilopsis domingensis and B. improvisus. Certain groups plotting symbols, except for sampling time 3, when n = 1. ND, no data.

were more abundant a few years before the oil spill (1981 to 1982) "Leafy algac" include Polysiphonia, Acanthophora, and Ceramium as common than in 1986 to 1987 at unoiled sites (Fig. 4), possibly because of genera; the most abundant sessile animals” include hydroids and sponges. natural fluctuations in abundance. After the spill, the cover of all Sampling dates: 1 = September to October 1981; 2 = January 1982; 3 = June 1982; 4 = July to August 1986; 5 - October to November 1986;

major groups was very greatly reduced in each oiled habitat (Fig. 4). 6 = February 1987; and 7 = May 1987. Results of repeated measures

There has been parchy recovery in the open habitat of foliose algae analysis of variance for oiled and unoiled sites after the spill are shown on

and sessile invertebrates, although not of the same relative abuncach graph, NS, P >0.05; ', P < 0.05; **, P < 0.01; ***, P<0.001. dance of species. In the channels, cover of both the oyster and

Percent cover on roots

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20

Live

Balanus

Live
Balanus

100

Oil

Oil

Oil

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Fig. 5. Abundance or biomass per sample of cight major infaunal taxa in three oiled (O) and four control (O) scagrass beds 5, 7, and 9 months after the oil spill (30). Means are plotted +1 SE, backtransformed from in (x + 1); some crror bars lic within the plotting symbols. “Burrowing shrimp" include alpheids (most abundant), processids, callianassids, and upogebids. NS, P>0.05; * P < 0.05 by repeated measures analysis of variance. Number per sample is shown at two scales. Data for polychactes are shown as grams per sample.

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barnack dropped gready and have since rocovered litde. False

70 mussets and barnacles disappeared in oiled rivers and were not

60 recorded again weil 15 months after the spill.

RT The greatest cover an roots in a ciled habicats after the spill was

SO 9 oil (Fig. 4). In addition, most roots sampled for epibiota (28) were

IN dead, broken, ar routing by August 1987 (54% on open coasts, 56%

30 in channck, and 66% in rivers oiled sites versus 8%, 1%, and 3%,

20 respectively, a mnoiled sites). Thus the mangrove-fringe roor habior has been largely destroyed a coled sites and will not be restored

5

10 unless new trees grow. Seagrasses. Extensive meadows of the seagrass Thalassia testudinum

30 cover much of the intertidal roof platforms and subcidal floors of

Crustoas

corallinen shallow embayments and lagoons along this coast (24). Entire beds of intercidal Thalassia were killed an some heavily oiled reef flats, as

10 shown by abundant oil-covered dead kaves washed ashore and dead bur intact root-rhizome mets (for comple, the site a Largo Remo

0 North) (Table 2). In contrass, suboidal Thalassia survived every

10

Halimeda where after the spill, alchongth kaves became brown and heavily fouled by algas for several months in heavily oiled areas.

80 Thalassia provides food, babies, and refuge for dense populations

ficroalgon of invertebrates and fishes (246, 29). Before the spill, amphipods, small decapods, optiuroids and other chinoderms, bivalves, gastro pocs, polychectes, and small fates were all abundant in seagrass within the study area (29) and all are in unoiled beds (Fig. 5). Sampling of infauna began September 1986 at three oiled and four unoiled sites (30 (Fig. 2). Four two of invertebrates were significandy less abundane in oiled grassbods afver the spill, but four others

20 showed no such difference (Fig. 5). Abundances of most cara increased between September and January; preliminary analyses of

10 body size indicate that recruitment caused these increases. Only the

0 abundance of harmic arabs ingrcared in oiled relative to unoiled arcas (7.3 versus 3.4 crabo per stampas, respectively, in January 1987,

Zoanthus P<0.05, repeated measures matysis of variance), perhaps because of a surplus of shells of recently dead snails (31).

Intertidel reef fests. Placforms of fringing reefs from extensive shallow to intercidal flass throughout the study region (Fig. 3) (7,9, 17, 32). Populations on the roof flar a Punta Galeta have been

2 monitored for up w 15 years (9) (Fig. 2). Damage was most antensive a the seaward borda, where the oil accumulated at low cick. Immediately after the spill a bloom of microalgae covered

Porites & recendy vacated subetracom (33) (Fig. 6). This area had been

Milleport dominated by perennial macroalgas particularly the fleshy red alga Lawrencia papillosa, custose corallines, and the articulated calcareous green alga Halimeda aprantia. Cover of all these plants was reduced to. kevels well below those observed previously, but had regained or

Palythoa exceeded typical abundance within 12 to 18 months, concurrent with a reduction of the microalgae. The most common sessile animals before the pill were zoanthids (Zoanthus sociatus and Palythoa spp.), hydrocorals (Millepora spp.), and scleractinian corals (Porites spp.). As the scaward border of the reef lat, populations of all these animals were severely reduced, and only Zoanthus had returned to typical abundance after 18 months (Fig. 6). Densities of sea urchins on the roof flat varied over three orders of magnitude

Porcont cover

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Echinometra before the spill (Fig. 6) (9. Ar the seaward edge, the most abundant

lucunter

100 Fig & Pre- and postspill comparisons of the abundance of algae and sessile animals (cop seven panels) and the sea urchin Echinometra luaunter (bottom

10 panel) on the scaward portion of the Galeta roof flat (33). Filled symbols denotes the heavily oiled zone dorest to the water's edge at low tide (Fig. 3); Open symbols and the sonoodh Kine in the E. facranter graph indicare less oiled (more handward) habitans, and more postspill surveys of percent cover

83 84 &S

87 that were significandy higher or lower than any prespill survey a P s 0.05

oll Spill and P s 0.õl, respectively. ladas, differences were significant only in

Your the heavily oiled zone (O). Covar was compared survey by survey with the use of paired teres marched by individual transects within surveys. Abundances of E. lucunter were compared with the use of residuals from regressions (34).

N 1000

Urchins per 10 m2

6 JANUARY 1969

ARTICLES 41

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urchin Echinometra lucunter was reduced by about 80% within a few Subtidal reefs. Populations of subtidal sessile organisms were days of oiling, and the reef Alat was littered with its skeletons. surveyed on six fringing reefs between Isla Margarita and Isla Although this decrease was small in an absolute sense relative to Grande within 1 year before and 4 months after the oil spill (Fig. 2) changes in abundance among years, it nevertheless departed signif. (41). These include the heavily oiled reef at Punta Galeta, a lightly candy from the average trend in abundance between months of May oiled reef at Isla Margarita, and four unoiled reefs cast of Portobelo. and June over the last 8 years (34). Farther inshore, no such Abundance of most common scleractinian coral genera in depths reductions occurred.

53 m decreased at Galeta by 51 to 96%, and total coral cover
Gonodactylid stomatopods (mantis shrimp) are abundant in decreased by 76%; even at 9 to 12 m the drop was 45% (Fig. 7).
intertidal Thalassia beds from Isla Margarita to Isla Largo Remo, Reductions were less at Isla Margarita and generally absent on the
where they live in and aggressively defend cavities in coral rubble at unoiled reefs, excepe at one site northeast of Portobelo (Fig. 2) for
densities up to 20 per square meter (35). They are prey for no apparent reason. This relation between amount of oiling on the
shorebirds, fish, and crabs, and in tum consume large numbers of six reefs and decrease in coral cover was significant for 0 to 3 m but
hermit crabs, snails, and other animals (36). Population dara are not deeper (42).
available for stomatopods from intertidal seagrass beds on four reef Sublethal effects were also substantial. Within Bahia las Minas,
Alats, including certain types of data collected at various times before most of the scleractinians still alive in depths less than 3 m showed
the spill (Table 2 and Fig. 2). Two of the sites were heavily oiled, signs of recent stress including bleaching or swelling of tissues,
and large amounts of oil were still present on mangrove roots and in conspicuous production of mucus, recendy dead areas devoid of
sandy sediment when sampling first began 3 months after the spill; coral tissue, and globules of oil (Fig. 3) (43). In some cases, bleached
the other two flats were at most lightly oiled. Densities of stomato- or dead areas were surrounded by a black halo characteristic of
pods were less on the heavily oiled flats, particularly for animals bacterial infeccion (44). Boch the frequency and size of recently dead
greater than 40 mm long (37). Loss of these large animals apparently lesions on the commonest massive corals increased markedly with
made larger cavities available to the survivors, which consequ the amount of oiling at each reef and decreased with water depth
fought less and suffered fewer injuries (38) compared to the same (Fig. 8) (45, 46). These effects were also species specific. In the case
sites before the spill and compared to lighdy oiled flats afterwards of S. siderea, which suffered most, new parcial mortality was still
(Table 2). Growth of larger survivors also increased on heavily oiled disproportionately common on heavily oiled reefs 1 year after the
Aars (39), probably because of decreased competition for cavities spill (46).
and an apparent population explosion of hermit crabs for food (35, The oil spill also affected other organisms, including snails on the
40). These effects have persisted in diminished form through our last reef Alat and intercidal zone at Punta Galeta and mobile cpifauna.
census in September 1987.

particularly shrimps above suboidal seagrasses. In summary, the spill
harmed prominent organisms in all intercidal and subtidal environ-

menos examined, infauna and epifauna, and members of all trophic
it

levels including primary producers, herbivores, carnivores, and

detritivorcs. int

Patterns of Responses and Their Significance

The severe damage to intercidal biocas and their response, such as
che Aush of ephemeral microalgae just after the spill, are similar to
those documented previously for other oiled intercidal communities
(47—50), including those inferred for Galeta after the Witwater spill
(4). Likewise, biological effects of spills are usually greatest in low
energy cnvironments, where oil tends to accumulate and be retained
in fine sediments, than in high energy environments where it is soon
washed away (50). This pattern matches the greater and more
persistent disturbance to riverine and channel mangrove root com-
munities than to those along open coasts and the rapid recovery it

abundance of many organisms at the seaward edge of the reef Alat
Heavily
Lightly

(Fig. 6).

In contrast, other results were not expected, and in some cases contradict widely held views about the effects of oil spills and the ways they are studied. First, extensive mortality of subridal corals and infauna of seagrasses had not been demonstrated before (1, 3) and contradicts undocumented assertions that these organisms are

not affected by oil spills. In part, subtidal effects may have been Percent cover beton oll spill

caused by the use of dispersant (51) but it seems unlikely that this Fig. 7. Percent cover of corals before the oil spill plotted against their cover

was the only reason, given the regional breadth of the impact and afterward. The diagonal lines represents no change in coral cover; points

the relatively small amount of dispersant employed (14). below this line indicate a decrease after the spill, and points above the line Second, the magnitude of subtidal coral mortality and injury show an increase. The points are means = 1 SE; some crror bars lic within within Bahia las Minas is in striking contrast to findings of no the plotting symbol. Oiling significantly affected coral cover only at the shallowest depth (42). Abbreviations: 3, 0-to 3-m depth: 6.3-70 -m depth lasting change in coral condition or growth after exposure to oil, and 12, 6 to 12-m depth. JUG and PALW are located just west of Isla

with or without chemical dispersant, in small-scale experiments (51, Grande, DMA and DONR are northeast of Portobelo, GAL is at Punta 52). Such discrepancies underlic the importance of detailed longGaleta, and MAR3 is at Isla Margarita (Fig. 2, half-filled circles).

term ecological studies, and the dangers inherent in extrapolation to

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DMA

DONA

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Porcent of colonies with recent Injury

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1126 colonies

4. K. Rutzlar and W. Sterrer, BioScience 20, 222 (1970). 5. C. Burkcland, A A. Reimer, J. R. Young, Survey of Marine Communities in Panama

and Experiments wish Oil (Publ. EPA-600/3-76-028, Environmental Protection

Agency Ecological Rescarch Series, Narragansen, RI, 1976). 6. J. D. Cubit at a., in 1987 OJ Spill Conference (Publ. 4452, American Petroleum

Institute, Washington, DC, 1987), pp. 401-406. 7. J. Cubit and S. Williams, Atoll Res. Bull. 269, 1 (1983). 8. J. D. Cubit, R C. Thompson, H. M. Caffey, D. M. Windsor, Smithsonian Contrib

Mar Sa. 32, 1 (1988); L. G. Macintyre and P. W. Glynn, Am. Assoc. Petrol. Geol

Bull. 60, 1054 (1976). 9. G. L. Hendler, in Proceedings of the Third Interational Coral Reef Symposium. D. L.

Tavlor, Ed. (University of Miami, Miami, FL 1977), vol. 1, pp. 217-223; J. D. Cubit, D. M. Windsor, R. C. Thompson, J. M. Burgen, Estuarine Coastal Shell Sa.

22, 719 (1986). 10. J. C. Ogden and E. H. Gladfcker, UNESCO Tech. Pap. Mar. Sa. 23, 1 (1983).

Important species in common throughout the tropical western Atlantic are red mangrove mangle, seagrass T testudinom, mos reef corals and algae, and

commercially important lobsters (Permalinus spp.) and oysters (C. reizophoree). 11. Ongoing drilling and refining off Yucatan and possible production along the west

coast of Florida 12. The oil type was 70% Venczuclan chade, 30% Mexican Isthmus crude, specific

gravity 27 (Amencan Petroleum Institute). Percent composition determined at the Bermuda Biological Station by cohamn chromatography with the use of alumina and subca gels: 47.4% saturates (fraction I, herane); 6.4% light aromatics (fraction 2, 10% ether/90% hexane); 4.8% heavy aromatics (fraction 3, 20% methylene chloride/80% hoxanc); 18.9% polar fraction (fraction 4, mcthylene

chlonde); and 22.5% unrecovered. 13. C. D. Getter, G. I. Scott, J. Michel, in 1981 Od Spill Conference (Publ. 75-4161.

American Petroleum Institute, Washington, DC. 1981), pp. 535-540. 14. Rcfincrv ofhcials estimated that <21.000 liters of Corcu 9527 (Epions Chemicals

America) were spraved from aircraft (6). STRI personnel observed thus spraving

berween Acana Chiquita and Punta Galeta. 15. J. D. Woodlev et al., Science 214, 749 (1981); J. H. Connell, ibid. 199, 1302

(1978). 16. Surveys beyond Punta Galeta began the first week of June 1986 and lasted 1

month. Vidcotapes were made of the coast berween Rio Chagres and Islas Naranjos. and scill photographs were made all along the coast. Visual assessments were made of degree of oiling (heavy, moderate, light, or absent) and the habitats

and types of organisms obvious affected. 17. J. D. Cubit, G. Batista de Yee, A. Roman, V. Batista, in Agonia de la Naturaleza, S.

Hackadon Moreno and ). Espinosa Gonzalez, Eds. (Impretes, Panama, 1985), pp.

183-199, Revista Medica Panama 9, 56 (1984). 18. Oil was observed commonly until the time of manuscripe revision (July 1988)

around Isla Pavardi, where it emerged directly from the coral landhu on which the refinery is built, and Punta Muerto, Bahia Cativa, castern Isla Largo Remo, and

Punta Galeta. 19. Within this area oil commonly escaped from sediments when we walked among

mangroves or cored into shallow subtidal scagrass beds. Interudal surfaces were

heavily coated with ou. 20. Most of the ow that escaped from Bahua Cativa was driven west. Coasts facing north

to northeast were heavily oued, whereas adjacent areas facing west or south received Littk oul. The best studied example is at the northwestern side of Isla Largo

Romo (Table 2). 21. These low tides occur annually at this time of year (8,9). Sea levels during most of

this time were as much as 10 cm below the 9-year average for this period of

normally low sea level. 22. Corals were collected by divers on davs when on surface slicks were visible, placed

in solvent rinsed aluminum foil, and frozen. Tissues were removed from skeletons with an air pick and homogenized with a tissue grinder. To minimize vanations due to water or carbonate inclusions, standard Lowrey protein determinations were used as one measure of tissue mass. After solvent atraction, total lipid weights were determined microgravimetrically. Extracts were fractionated by adsorption chromatography. Hydrocarbons were analyzed with a capillary gas chromatograph cqmpped with a flamc ionizabon detector and 25-m SÉ 52 fused

silica columns 23. R H Green, Sampling Design and Statistical Methods for Environmental Biologists

(Wiley, New York, 1979). 24. J. B. C. Jackson, Bull. Mer. Sci. 23, (1973); K. L. Heck. Mer. Biol. 41, 335 (1977);

R Vasquez-Montoya, An. Inst. Cienc. Mar. Limnol. Univ. Nac. Auton. Mex. 10,1

(1983) 25. This estimate was extrapolated from acrial photographs of 36 km of the 82-km

shorelinc, of which 76 km contains mangroves. Of the photographed shorelinc,

36% contained a band of dead mangroves. 26. Sprouting success was measured for seedlings collected from an unoiled site, and

planted in one unoiled and two oiled sites. Of 25 scodlings transplanted into cach

site, 16 (64%) sprouted at the unoiled site and 1 (2%) sprouted at the oiled sites. 27. J. P. Sutherland. Mar. Biol. 58, 75 (1980); W. E. Odum, C. C. McIvor, T. J. Smith

HI, The Ecology of the Mangroves of South Florida: A Community Profile (Publ. 81/24,

U.S. Fish Wildlife Service, Washington, DC, 1982). 28. Roots were sampled three times before the spill in rivers and channels (September

to October 1981, January 1982, and Junc 1982) and twice in open habitats (September to October 1981 and January 1982). Several areas of shore within cach habitat were chosen haphazardly. Fifteen to 25 intertdal roots 2 20 cm long that had not become firmly attached to the mud were lifted from the water, and cover of attached organisms was measured for cach root by 100 random point counts after the oil spill or was estimated visually before the spill. Afte the spill previously sampled riverinc and channel habitats included both oiled and unoiled sites but all open sites were oiled. Thus it was necessary to choose sites near Portobelo (Fig. 2),

Sid
Dip Por
sd

> 10%

Mortcity

Nono

Moderate

Heavy

Amount of olling

Fig. 8. Frequency of injury for the three most common species of massive corals in relation to the amount of oiling a 12 reefs (4 unoiled, 3 lightly to moderately oiled, and 5 heavily oiled). Open bars represent coral colonies with injuncs that did not exceed 10% of the surface area of the coral; filled bars represent injuries greater than 10% (maximum observed, 100%). Sample sizes are shown above cach category of oiling. Abbreviations; Dip, Diplona divosa; Por, Pontes astreoides; Sid, Siderastrea siderea; s, shallow (0 to 1 m), and d, deep (1 to 2 m).

natural populations from laboratory-based physiological data or small-scale, short-term press perturbation experiments in the field (2, 3, 48, 52, 53).

Third, sublethal effects are extensive and may be more important in the long term than initial mortality (3, 48). Changes in stomato pod behavior and population structure were more pronounced than might be expected from a simple reduction in numbers. Likewise, injury of corals has allowed colonization of their bare skeleton by algae and other sessile organisms that may overgrow parts of colonies that survived the initial effects of oil (3, 54). Corals stressed by oil are probably also more susceptible to cpidemic discasc and likely to grow and reproduce more slowly than unaffected colonics (3, 5, 52). Any combination these effects may further reduce overall abundance of corals as much as the initial spill (54). Such a chain reaction could continue long after any petroleum hydrocarbons are present in the environment or coral issues, just as staghom coral continued to decline precipitously following a severe hurricane in Jamaica (55)

The response of organisms to an oil spill, or any other major disturbance, will depend on the conditions in which they normally live (15, 48, 56). Moreover, the suite of organisms able to survive under conditions of chronic pollution, and their resistance to further stress, is typically different from that in similar unpolluted habitats (48, 57). Much of Bahia las Minas has been subjected to human disturbance, beginning with decades of excavation, dredging, and landfilling for the construction of the Panama Canal and the City of Colon, drainage and spraying of mangroves for mosquito control, construction of the refinery and a large cement plant on landfill, a major oil spill in 1968, and unknown amounts of chronic oil pollution from the refinery and ships passing to and from the Canal (4, 5, 17, 58). It is a mcasure of the severity of the 1986 oil spill that the biological consequences were so detectable despite this history of environmental abuse.

REFERENCES AND NOTES

1. National Research Council, Oil in the Sea: Inputs, Fetes, & Efas (National Academy

Press, Washington, DC, 1985). 2. R. B. Clark, Philos. Trans. R. Soc. London Ser. B 297, 185 (1982); R S. Carney,

Am. Sa 74, 298 (1986). 3. Y. Loya and B. Rinkevich, Mar Ecol. Prog. Ser. 3, 167 (1980).

6 JANUARY 1989

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