In 1986 more than 8 million liters of crude oil spilled into a complex region of mangroves, seagrasses, and coral reefs just east of the Caribbean entrance to the Panama Canal. This was the largest recorded spill into coastal habitats in the tropical Americas. Many populations of plants and animals in both oiled and unoiled sites had been studied previously, thereby providing an unprecedented measure of ecological variation before the spill. Documentation of the spread of oil and its biological effects begun immediately. Intertidal mangroves, seagrasses, algae, and associated invertebrates were covered by oil and died soon after. More surprisingly, there was also extensive mortality of shallow subtidal reef corals and infauna of seagrass beds. After 1.5 years only some organisms in areas exposed to the open sea have recovered.

O

IL POLLUTION IN THE SEA HAS BEEN A MAJOR ENVIRON

mental problem for several decades, but we know remarkably little about the effects of oil on natural populations and communities (1). Uptake of oil and physiological responses of organisms have been investigated in the laboratory or field, sometimes coupled with short-term monitoring of communities and of amounts of oil in water, sediments, and organisms (2, 3). Investigations of oil spills generally commence after any initial damage has occurred, and baseline coological data are usually lacking. This approach precludes measurement of the effect of oil spills because there usually is no knowledge of natural ecological variation (2). Such was the case in 1968 following the release of 3.2 million liters of oil from the wreck of the Witwater near the Galeta Marine Laboratory (Smithsonian Tropical Research Institute) in Panama (4, 5). Another even larger spill occurred in the same region in 1986 (6) (Fig. 1). In this article, we describe the types and extent of damage to coastal populations and communities in the first 1.5 years after the 1986 spill, and contrast our findings with earlier work and widely held views regarding the effects of oil on tropical coastal communities.

The authors are resident or visiting investigators at the Smithsonian Tropical Research Institute (STRI), Apartado 2072 Balboa, Republic of Panama. Institutional affiliations of authors not employed by STRI are as follows: K. Burns and A. H. Knap, Bermuda Biological Station for Research, Bermuda GEO1; R. L. Caldwell, Department of Zoology, University of California, Berkeley, CA 94720, C. D. Getter, 915 Academy Street, N.E., Salem, OR 97303; R. Seeger, University of California, Berkeley, Richard Gump Biological Research Station, B.P. 244 Temac, Moorea, French Polynesia; and E. Weil, Department of Zoology, University of Texas, Ausan, TX 78712, and Fundacion Cientifica Los Roques, Apartado 1, Caracas 1010A, Venezuela.

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Our study is unique for two reasons. First, many of the habitats damaged by oil have been investigated since the Witwater spill 18 years before. Results of this research have been published in more than 130 articles, and the flora and fauna are well known taxonomi

cally (7). Detailed time-series data on the physical environment and biota (8, 9) provide a measure of natural variation before the more recent oil spill against which subsequent events can be compared. Second, observations of the effects of the spill began as oil was coming ashore. Of additional importance, the coastal environments (including seagrass beds, mangroves, algal flats, and coral reefs) and most of the species affected are similar to those throughout the

Caribbean, Gulf of Mexico, and southeastern United States (10). Thus our observations are relevant to assessment of potential biological effects of pollution in several areas where extraction or refining of oil is ongoing on planned (11).

On 27 April 1986 at least 8 million liters of medium-weight crude oil (12) spilled from a ruptured storage tank into the sea on the Caribbean coast of Panama (6) (Fig. 2). This is the greatest amount of oil spilled directly into a sheltered coastal habitat in the tropical Americas (3, 13). For 6 days, onshore winds held the oil within Bahia Cativa adjacent to the refinery (Fig. 2), but runoff from rains and shifting winds then flushed the oil out to sea. At this time dispersant was sprayed on slicks in the mouth of Bahia las Minas and offshore (14). By 15 May, the oil had swept across fringing reefs and entered mangrove forests, small estuaries, and sand beaches within 10 km of the refinery.

Table 1. Comparison of visual assessment of amount of oiling on four coral reefs (ranked heavy (H), moderate (M), and none (N)] with results of gas chromatographic (GC) analyses of saturated hydrocarbons in coral tissues and by ultraviolet fluorescence (UVF) analyses of aromatic hydrocarbon fractions. Oil content by GC was conservatively estimated as the unresolved hydrocarbons in the elution range for alkanes containing 12 to 36 carbon atoms. Oil units by UVF were determined by comparison with the spilled oil. Values are expressed as micrograms per milligram of coral tissue (lipid or protein) and are the mean and standard deviation of triplicate analyses. Reefs are listed from west to east (Fig. 2); Payardi West is adjacent to the refinery and Palina West is just west of Isla Grande.

Plants and animals died wherever they came in contact with oil. However, the types and magnitude of effects varied greatly with coastal topography and location, and among habitats and taxa. Such complex effects are similar to those of powerful hurricanes on Jamaican and Australian coral reefs (15). We first consider the spatial pattern of the spill and its effects in different environments, including variations in effects on different taxa. We then describe the patterns of responses of different organisms that discuss prospects for recovery.

Spatial Distribution of Oil Among Habitats

The distribution of oil within 2 months of the spill was visually assessed by aerial surveys between Rio Chagres, 27 km west of the refinery, and Punta San Blas, 98 km to the east, and by boat and foot from Rio Chagres to Nombre de Dios (16) (Fig. 2). No oil was observed on shorelines east of Isla Grande, and only a few patches were observed east of Maria Chiquita and west of the Panama Canal entrance. Heavy oiling occurred along most of the coast between Isla Margarita and Islas Naranjos (Fig. 2). The straight-line distance between these two points is 11 km, but the labyrinthine shoreline is at least 82 km long and contains about 16 km2 of mangroves and 8 km2 of intertidal reef flats and subtidal reefs (17). Within this area, the only large unoiled areas 2 months after the spill were two mangrove lagoons that are isolated from open water by narrow channels (hatched areas in Fig. 2). Oil slicks ranging from a metallic sheen to brown patches are still common between Punta Muerto and Galeta, especially after heavy rains flush oil from mangroves and from the landfill beneath the refinery (18).

Within similar habitats, distance from the refinery, direction of oil movement, and water depth apparently caused considerable variation in the degree of oiling even in the most polluted region. Amounts of oil observed on or in sediments of seagrass beds, mangroves, and over reef flats were highest within a few kilometers of the refinery (Punta Muerto to Largo Remo and Punta Galeta)