and much less at Islas Naranjos and Isla Margarita (19). Moreover, similar differences occurred over just a few hundred meters between shores directly exposed to or sheltered from the wind-driven oil (20). On an even smaller scale, extreme low tides between 10 and 19 May (6, 21) caused oil to accumulate along the seaward borders of reef flats, whereas just shoreward much less oil contacted the substratum. In general, intertidal habitats just above mean low water were the most heavily oiled, including mangrove roots and sedi Fig. 2. Region of the Republic of Panama affected by the 27 April 1986 oil spill, shown as increasing enlargements (A to C). (A) Location within Panama, just cast of the Caribbean entrance to the Panama Canal. (B) The boxed area includes the most heavily oiled coastal habitats. Punta Galeta, inside the boxed area, is 9°24′N, 79′52′′W. Lightly oiled and unoiled study sites are cast of Bahia las Minas, near Portobelo and Isla Grande. (C) Detail of the most heavily oiled area and location of study sites. Encircled "R" on Isla Pavardi marks the refinery where the oil spill occurred. Horizontal hatching denotes embayments where little oil penetrated. Symbols for types of study sites (open symbols, unoiled or lightly oiled sites; filled symbols, oiled sites): A, mangrove root,, seagrass bed; O, subtidal coral reef, data collected only after the oil spill; 0, subtidal coral reef, data collected both before and after the oil spill: the four sites near Portobelo and Isla Grande were not oiled, the site at Isla Margarita was moderately oiled, and the site at Punta Galeta was heavily oiled; O, reef-flat stomatopods; multirayed star, reef flat community, Punta Galeta; six-rayed symbol, mangrove forest. 5 km Fig. 3. Organisms and habitats affected by the April 1986 oil spill at Bahia las Minas, Panama (all photographs by C. Hansen except (D) by S. D. Garrity). (A) Oil accumulated along the scaward edge of the Galeta reef flat at low tide (scen as the dark border in the cover photo), directly coating and killing plants and animals, including the zoanthid Palythoa sp. (lighter patches in foreground) and the hydrocoral Millepon sp. ing through oil in background). (B) Ar oil accumulated along sand beaches, whe soaked into the sand and settled onto the shoreward reef flat at low tide, killing seagrasses, algac and invertebrates. The rectangular objects in the foreground are polyurethane mattresses used by cleanup crews to absorb oil. (C) Underwater view of the coral S. sideves partially killed by oil (horizontal length in the photograph, 12 cm). Live tissue forms the dark reddish area at the bottom. The central, light-colored area is skeleton showing through partially dead tissue, which is also being colonized by algae. The lightest area at the top is bare skeleton covered by a film of microalgae. (D) Oil-covered intertidal surfaces of prop roots of the red mangrove, R. mangle, killing oysters and other epibiota on the roots. Relieved of the weight of their leaves, defoliated branches ficned upward, lifting the roots out of the water and thus killing subtidal epibiota that previously escaped direct contact with floating oil. (E) Dead mangrove trees form a band about 8 to 100 m wide (February 1987), marking the area where oil accumulated as it entered the mangrove forests (horizontal distances: foreground -0.4 km and background -1.3 km). A band of defoliated trees was apparent within 2 months after the spill and widened thereafter. 6 JANUARY 1989 ARTICLES 39 Fig. 4. Percent cover of formerly abundant taxa and oil on mangrove roots in riverine, channel, and open coast habitats before and after the oil spill. O, Prespill data; O, unoiled sites; and, oiled sites. Means are plotted 1 SE, converted from arcsine transformations. Some error bars lie within the plotting symbols, except for sampling time 3, when n = 1. ND, no data. "Leafy algae" include Polysiphoma, Acanthophora, and Ceramium as common genera; the most abundant "sessile animals" include hydroids and sponges. Sampling dates: 1 = September to October 1981; 2= January 1982; 3 = June 1982; 4 = July to August 1986; 5 October to November 1986; 6 February 1987; and 7 May 1987. Results of repeated measures analysis of variance for oiled and unoiled sites after the spill are shown on each graph, NS, P > 0.05; *, P < 0.05; **, P < 0.01; ***, P < 0.001. sis of aromatic hydrocarbon fractions (22). Preliminary results generally parallel classification of sites based on visual inspection, as shown here for the concentration of saturated hydrocarbons in tissues of the coral Siderastrea sidera (Table 1). Biological Effects Consequences of the spill were assessed differently, depending on the types of data available from before the oil spill (23). Ideally, biological parameters should have been measured at oiled and unoiled sites before and after the spill. This condition was satisfied for biota of mangrove roots and subtidal corals. Extensive prespill data are available for the reef flat at Galeta, but there are no control sites and effects must be inferred from temporal change and from the spatial distribution of oiling on the reef flat. In contrast, there are little or no appropriate prespill data for subtidal seagrass communities. In this case, comparisons were made between oiled and unoiled sites after the spill, confounding the treatment (oiling) and geogra 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 habitat is still more limited than in other habitats studied. Mangrove communities. Red mangrove, Rhizophora mangle, forms 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 heavily oiled sites did not produce new leaves, in contrast to transplants at an unoiled site (26). The prop roots of R. mangle are overgrown by algae and invertebrates that vary in species composition with exposure to the 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 ocean were covered with foliose algae and sessile invertebrates such as sponges, hydroids, and ascidians. In mangrove channels, the edible oyster, Crassostrea rhizophorae, and a barnacle, Balanus improvisus, were most abundant on roots. Roots in small rivers were dominated by the false mussel Mytilopsis domingensis and B. improvisus. Certain groups were more abundant a few years before the oil spill (1981 to 1982) than in 1986 to 1987 at unoiled sites (Fig. 4), possibly because of natural fluctuations in abundance. After the spill, the cover of all major groups was very greatly reduced in each oiled habitat (Fig. 4). There has been patchy recovery in the open habitat of foliose algae and sessile invertebrates, although not of the same relative abundance of species. In the channels, cover of both the oyster and Fig. 5. Abundance or biomass per sample of eight major infaunal taxa in three oiled () and four control (O) seagrass beds 5, 7, and 9 months after the oil spill (30). Means are plotted ±1 SE, backtransformed from In (x + 1); some error bars lie 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 rwo scales. Data for polychaetes are shown as grams per sample. 80 60 40 20 Ophiuroide Grams per sample barnacle dropped greatly and have since recovered little. False mussels and barnacles disappeared in oiled rivers and were not recorded again until 15 months after the spill. The greatest cover on roots in all oiled habitats after the spill was oil (Fig. 4). In addition, most roots sampled for epibiota (28) were dead, broken, or rotting by August 1987 (54% on open coasts, 56% in channels, and 66% in rivers at oiled sites versus 8%, 1%, and 3%, respectively, at unoiled sites). Thus the mangrove-fringe root habitat has been largely destroyed at oiled sites and will not be restored unless new trees grow. Seagrasses. Extensive meadows of the seagrass Thalassia testudinum cover much of the intertidal reef platforms and subtidal floors of shallow embayments and lagoons along this coast (24). Entire beds of intertidal Thalassia were killed on some heavily oiled reef flats, as shown by abundant oil-covered dead leaves washed ashore and dead but intact root-rhizome mats (for example, the site at Largo Remo North) (Table 2). In contrast, subtidal Thalassia survived everywhere after the spill, although leaves became brown and heavily fouled by algae for several months in heavily oiled areas. Thalassia provides food, habitat, and refuge for dense populations of invertebrates and fishes (24, 29). Before the spill, amphipods, small decapods, ophiuroids and other echinoderms, bivalves, gastropods, polychaetes, and small fishes were all abundant in seagrass within the study area (24) and still are in unoiled beds (Fig. 5). Sampling of infauna began September 1986 at three oiled and four unoiled sites (30) (Fig. 2). Four taxa of invertebrates were significantly less abundant in oiled grassbeds after the spill, but four others showed no such difference (Fig. 5). Abundances of most taxa increased between September and January; preliminary analyses of body size indicate that recruitment caused these increases. Only the abundance of hermit crabs increased in oiled relative to unoiled areas (7.3 versus 3.4 crabs per sample, respectively, in January 1987, P < 0.05, repeated measures analysis of variance), perhaps because of a surplus of shells of recently dead snails (31). Intertidal reef flats. Platforms of fringing reefs from extensive shallow to intertidal flats throughout the study region (Fig. 3) (7, 9, 17, 32). Populations on the reef flat at Punta Galeta have been monitored for up to 15 years (9) (Fig. 2). Damage was most extensive at the seaward border, where the oil accumulated at low tide. Immediately after the spill a bloom of microalgae covered recently vacated substratum (33) (Fig. 6). This area had been dominated by perennial macroalgae, particularly the fleshy red alga Laurencia papillosa, crustose corallines, and the articulated calcareous green alga Halimeda opuntia. Cover of all these plants was reduced to. levels well below those observed previously, but had regained or exceeded typical abundance within 12 to 18 months, concurrent with a reduction of the microalgae. The most common sessile animals before the spill were zoanthids (Zoanthus sociatus and Palythoa spp.), hydrocorals (Millepora spp.), and scleractinian corals (Porites spp.). At the seaward border of the reef flat, 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 reef flat varied over three orders of magnitude before the spill (Fig. 6) (9). At the seaward edge, the most abundant Urchins per 10 m2 100 10 Palythoa Echinometra lucunter Fig. 6. Pre- and postspill comparisons of the abundance of algae and sessile animals (top seven panels) and the sea urchin Echinometra lucunter (bottom panel) on the seaward portion of the Galeta reef flat (33). Filled symbols denotes the heavily oiled zone closest to the water's edge at low tide (Fig. 3). Open symbols and the smooth line in the E. cunter graph indicate less oiled (more landward) habitats; * and + mark postspill surveys of percent cover that were significantly higher or lower than any prespill survey at P ≤ 0.05 and P ≤ 0.01, respectively. In all cases, differences were significant only in the heavily oiled zone (). Cover was compared survey by survey with the use of paired t tests matched by individual transects within surveys. Abundances of E. lucunter were compared with the use of residuals from regressions (34). 1 83 84 85 86 87 88 Oil Spill Year 6 JANUARY 1989 ARTICLES 41 urchin Echinometra lucunter was reduced by about 80% within a few days of oiling, and the reef flat was littered with its skeletons. Although this decrease was small in an absolute sense relative to changes in abundance among years, it nevertheless departed significantly from the average trend in abundance between months of May and June over the last 8 years (34). Farther inshore, no such reductions occurred. Gonodactylid stomatopods (mantis shrimp) are abundant in intertidal Thalassia beds from Isla Margarita to Isla Largo Remo, where they live in and aggressively defend cavities in coral rubble at densities up to 20 per square meter (35). They are prey for shorebirds, fish, and crabs, and in turn consume large numbers of hermit crabs, snails, and other animals (36). Population data are available for stomatopods from intertidal seagrass beds on four reef flats, including certain types of data collected at various times before the spill (Table 2 and Fig. 2). Two of the sites were heavily oiled, and large amounts of oil were still present on mangrove roots and in sandy sediment when sampling first began 3 months after the spill; the other two flats were at most lightly oiled. Densities of stomatopods were less on the heavily oiled flats, particularly for animals greater than 40 mm long (37). Loss of these large animals apparently made larger cavities available to the survivors, which consequently fought less and suffered fewer injuries (38) compared to the same sites before the spill and compared to lightly oiled flats afterwards (Table 2). Growth of larger survivors also increased on heavily oiled flats (39), probably because of decreased competition for cavities and an apparent population explosion of hermit crabs for food (35, 40). These effects have persisted in diminished form through our last census in September 1987. Subtidal reefs. Populations of subtidal sessile organisms were surveyed on six fringing reefs between Isla Margarita and Isla Grande within 1 year before and 4 months after the oil spill (Fig. 2) (41). These include the heavily oiled reef at Punta Galeta, a lightly oiled reef at Isla Margarita, and four unoiled reefs cast of Portobelo. Abundance of most common scleractinian coral genera in depths ≤3 m decreased at Galeta by 51 to 96%, and total coral cover decreased by 76%; even at 9 to 12 m the drop was 45% (Fig. 7). Reductions were less at Isla Margarita and generally absent on the unoiled reefs, except at one site northeast of Portobelo (Fig. 2) for no apparent reason. This relation between amount of oiling on the six reefs and decrease in coral cover was significant for 0 to 3 m but not deeper (42). Sublethal effects were also substantial. Within Bahia las Minas, most of the scleractinians still alive in depths less than 3 m showed signs of recent stress including bleaching or swelling of tissues, conspicuous production of mucus, recently dead areas devoid of coral tissue, and globules of oil (Fig. 3) (43). In some cases, bleached or dead areas were surrounded by a black halo characteristic of bacterial infection (44). Both the frequency and size of recently dead lesions on the commonest massive corals increased markedly with the amount of oiling at each reef and decreased with water depth (Fig. 8) (45, 46). These effects were also species specific. In the case of S. siderea, which suffered most, new partial mortality was still disproportionately common on heavily oiled reefs 1 year after the spill (46). The oil spill also affected other organisms, including snails on the reef flat and intertidal zone at Punta Galeta and mobile epifauna, particularly shrimps above subtidal seagrasses. In summary, the spill harmed prominent organisms in all intertidal and subtidal environments examined, infauna and epifauna, and members of all trophic levels including primary producers, herbivores, carnivores, and detritivores. Fig. 7. Percent cover of corals before the oil spill plotted against their cover afterward. The diagonal lines represents no change in coral cover; points below this line indicate a decrease after the spill, and points above the line show an increase. The points are means ± SE; some error bars lie within the plotting symbol. Oiling significantly affected coral cover only at the shallowest depth (42). Abbreviations: 3, 0- to 3-m depth; 6. 3- to 6-m depth; and 12, 6- to 12-m depth. JUG and PALW are located just west of Isla Grande, DMA and DÖNR are northeast of Portobelo, GAL is at Punta Galeta, and MAR3 is at Isla Margarita (Fig. 2, half-filled circles). Patterns of Responses and Their Significance The severe damage to intertidal biotas and their response, such as the flush of ephemeral microalgae just after the spill, are similar to those documented previously for other oiled intertidal communities (47–50), including those inferred for Galeta after the Witwater spill (4). Likewise, biological effects of spills are usually greatest in low energy environments, 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 communities than to those along open coasts and the rapid recovery in abundance of many organisms at the seaward edge of the reef flat (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 subtidal 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 caused by the use of dispersant (51) but it seems unlikely that this was the only reason, given the regional breadth of the impact and the relatively small amount of dispersant employed (14). Second, the magnitude of subtidal coral mortality and injury within Bahia las Minas is in striking contrast to findings of no lasting change in coral condition or growth after exposure to oil, with or without chemical dispersant, in small-scale experiments (51, 52). Such discrepancies underlie the importance of detailed longterm ecological studies, and the dangers inherent in extrapolation to Fig. 8. Frequency of injury for the three most common species of massive corals in relation to the amount of oiling at 12 reefs (4 unoiled, 3 lightly to moderately oiled, and 5 heavily oiled). Open bars represent coral colonies with injuries 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 each category of oiling. Abbreviations; Dip, Diplona clivosa, Por, Porites 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 stomatopod 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 epidemic disease and likely to grow and reproduce more slowly than unaffected colonies (3, 5, 52). Any combination of 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 tissues, just as staghorn 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 measure 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, Fates, & Effects (National Academy Press, Washington, DC, 1985). 2. R. B. Clark, Philos. Trans. R. Soc. London Ser. B 297, 185 (1982); R. S. Carney, Am. Sci. 74, 298 (1986). 3. Y. Loya and B. Rinkevich, Mar. Ecol. Prog. Ser. 3, 167 (1980). 6 JANUARY 1989 4. K. Rutzler and W. Sterrer, BioScience 20, 222 (1970). 5. C. Birkeland, A. A. Reimer, J. R. Young, Survey of Marine Communities in Panama and Experiments with Oil (Publ. EPA-600/3-76-028, Environmental Protection Agency Ecological Research Series, Narragansett, RI, 1976). 6. J. D. Cubit et al., in 1987 Oil 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. Sci. 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 International 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. Burgett, Estuarine Coastal Shelf Sci. 22, 719 (1986). 10. J. C. Ogden and E. H. Gladfekter, UNESCO Teck. Pap. Mar. Sci. 23, 1 (1983). Important species in common throughout the tropical western Atlantic are red mangrove R. mangle, seagrass T. testudinum, most reef corals and algae, and commercially important lobsters (Paulinus spp.) and oysters (C. rhizophorae). 11. Ongoing drilling and refining off Yucatan and possible production along the west coast of Florida. 12. The oil type was 70% Venezuelan crude, 30% Mexican Isthmus crude, specific gravity 27 (American Petroleum Institute). Percent composition determined at the Bermuda Biological Station by column chromatography with the use of alumina and silica gels: 47.4% saturates (fraction 1, hexane); 6.4% light aromatics (fraction 2, 10% ether/90% hexane); 4.8% heavy aromatics (fraction 3, 20% methylene chloride/80% hexane); 18.9% polar fraction (fraction 4, methylene chloride); and 22.5% unrecovered. 13. C. D. Getter, G. I. Scott, J. Michel, in 1981 Oil Spill Conference (Publ. 75-4161, American Petroleum Institute, Washington, DC. 1981), pp. 535-540. 14. Refinery officials estimated that <21,000 liters of Corexit 9527 (Exxons Chemicals America) were spraved from aircraft (6). STRI personnel observed this spraying between Agaria Chiquita and Punta Galeta. 15. J. D. Woodley 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. Videotapes were made of the coast between Rio Chagres and Islas Naranjos, and still 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 obvioush affected. 17. J. D. Cubit, G. Batista de Yee, A. Roman, V. Batista, in Agonia de la Naturaleza, S. Heckadon Moreno and J. Espinosa Gonzalez, Eds. (Impretex, Panama, 1985), pp. 183-199, Revista Medica Panama 9, 56 (1984). 18. Oil was observed commonly until the ume of manuscript revision (July 1988) around Isla Pavardi, where it emerged directly from the coral landfill 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 seagrass beds. Intertidal surfaces were heavily coated with oil. 20. Most of the oil that escaped from Bahia Cativa was driven west. Coasts facing north to northeast were heavily oiled, whereas adjacent areas facing west or south received little oil. The best studied example is at the northwestern side of Isla Largo Remo (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 days 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 variations due to water carbonate inclusions, standard Lowrey protein determinations were used as one measure of tissue mass. After solvent extraction, total lipid weights were determined microgravimetrically. Extracts were fractionated by adsorption chromatography. Hydrocarbons were analyzed with a capillary gas chromatograph equipped with a flame ionization detector and 25-m SE 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. Mar. Sc. 23, (1973); K. L. Heck, Mar. 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 aerial photographs of 36 km of the 82-km shoreline, of which 76 km contains mangroves. Of the photographed shoreline, 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 seedlings transplanted into each 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 III, 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 June 1982) and twice in open habitats (September to October 1981 and January 1982). Several areas of shore within each habitat were chosen haphazardly. Fifteen to 25 intertidal roots ≥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 each root by 100 random point counts after the oil spill or was estimated visually before the spill. Afte the spill, previously sampled riverine 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), ARTICLES 43 |