Oil Pollution: Damage Observed in Tropical Communities along the Atlantic Seaboard of Panama Author(s): Klaus R?tzler and Wolfgang Sterrer Source: BioScience, Vol. 20, No. 4 (Feb. 15, 1970), pp. 222-224 Published by: American Institute of Biological Sciences Stable URL: http://www.jstor.org/stable/1295129 Accessed: 17/04/2009 12:18 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=aibs. 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American Institute of Biological Sciences is collaborating with JSTOR to digitize, preserve and extend access to BioScience. http://www.jstor.org Oil Pollution Damage observed in tropical communities along the Atlantic seaboard of Panama Klaus Riitzler and Wolfgang Sterrer From 18 to 22 February 1969, approxi- mately 2 months after the wreck of the oil tanker Witwater (13 December 1968), we had the opportunity to visit the site of the event to make a preliminary study of the effects of oil pollution on marine habitats. The incident occurred approximately 2 nautical miles northeast of Galeta Is- land, Canal Zone, where the marine facil- ity of the Smithsonian Tropical Research Institute is located (Fig. 1). The 3400-ton tanker S. S. Witwater ruptured on its way to the Atlantic entrance of the Panama Canal. Close to 20 thousand barrels of diesel oil and Bunker C were released during and after the accident and driven toward the Galeta Island shoreline by the strong onshore seasonal winds (Fig. 2). By avoiding the use of detergents, which proved to be fatal to marine life during the well known Torrey Canyon wreckage (Scilly Isles) and by burning and pumping off the oil which had ac- cumulated under the force of onshore winds in a small bay adjacent to the Galeta Laboratory, the Smithsonian Tropical Research Institute staff, in col- Fig. 1. Aerial view of the Smithsonian Tropi- cal Research Institute Marine Laboratory, Galeta Island. laboration with members of the local military forces had considerably reduced the threat of severe damage to marine life. Fig. 2. Oil drifting toward the Galeta Island shore near the Marine Laboratory. Unfortunately, because of the very recent initiation of research on inverte- brate groups at the Galeta Laboratory, information available about the composi- tion of the nearby biota in the unpolluted state is incomplete and concentrates on vertebrate populations only. However, by comparing our observations with data from other better known areas in the tropical Atlantic, we obtained a good impression of the actual and potential damage to the flora and fauna of the various habitats caused by the oil spillage. Rocky Shores Since oil untreated with detergents is floating on the surface, it is the intertidal biota which suffer most from a spill. A great percentage of the affected shore consists of exposed rocky coast, mainly the Fort Randolph area and the causeway leading to the Galeta Laboratory. High winds caused a spray of mixed seawater and oil to cover trees and shrubs in the supralittoral zone to a height of 2 m above mean tide level; the oil has' already killed many of these plants. Supralittoral spray pools and upper mesolittoral tide pools are still covered with a layer of oil up to 2 cm deep and are devoid of life (Fig. 3). Thanks to the strong water agitation pro- ducing water-in-oil emulsions, the lower mesolittoral and the infralittoral zones were only temporarily affected by oil. The waves, as soon as they had discharged their oil, already started to erode it again. Also, the rapid action of the emergency crew, who by pumping and burning elim- inated large quantities of oil (Fig. 4) be- fore the tide had withdrawn, helped to lessen the effects in these zones. Never- theless, damage to the gastropod and barnacle populations has to be assumed. Wherever rocks and driftwood are fully exposed to the sun at low tide, the oil layer is slowly being reduced to a thin crust of tar and the substrates are being repopulated by the usual variety of inter- tidal organisms. Coral Reefs Although the water was very agitated and turbid during our visit, we were able to dive in shallow water. The reefs seemed to be the least affected communities of all. Shallow coral patches, consisting mainly of Porites furcata, P. asteroides, Siderastrea radians, Millepora Com- planata (a hydrocoral), and associated organisms showed no ill effects at the time of the survey. This can be explained Fig. 3. Oil-covered supralittoral spray pool near Fort Randolph. Dr. Riitzler is with the department of invertebrate zoology, Smithsonian Institution, Washington, D.C. 20560. Dr. Sterrer is with the Bermuda Biological Station for Research, St. George's West, Bermuda. 222 BioScience Vol. 20 No. 4 by the fact that these corals were subtidal and did not come into direct contact with the oil, which is mainly confined to the air-water interface. Further, due to high winds, water level at low tide was higher than usual; some of the corals observed would probably be partly exposed during very low tides, but they were not exposed or affected by oil during this period. Sandy Beaches Below a blackish oil-stained supralit- toral zone, the sandy beaches of the affected area looked clean, at first glance. However, below a recently accumulated clean layer (2-5 mm), the sand was per- meated completely with oil. In contrast to the rocky shore, sandy beaches as well as mangrove swamps have a rather hori- zontal than vertical extension (flat angle of exposure), and a large "internal" sur- face. They act as huge natural filters for the water masses brought in by waves and tides. In the case of the sandy beach, still another phenomenon has to be consid- ered, that of the subterranean backflow of water. With every wave breaking and running dead, a considerable amount of water is transported up the beach. Whereas most of the lower portion of this water body flows back on top of the sand, most of the upper portion filters vertically into the sand (Sterrer, 1965). Rough ob- servations showed that, taking a wave Fig. 4. Burning of oil which was trapped in a small bay next to the Galeta Marine Lab- oratory. period of 10 sec, and a water layer 1 mm thick as a basis, this means that 86,400 liters of water are filtered through I m of surfaces and per 24 hr. This consider- able amount of water, then, together with the fresh groundwater, creates a con- tinuous stream which-depending on local conditions-may continue for hundreds of meters underneath the sea bottom. In the case of an oil spill, this means that the surface oil film brought ashore is deposited on top of the sand when the water soaks in and is pressed down by the TABLE 1. Oil sand Unaffected sand Panama Florida Morehead City, N.C. Ciliata 45 - 32 Turbellaria 3b 38 243 Nematoda 6 22 8.000 Archiannelida - 100 Other Annelida 6 4 40 Copepoda - 18 45 Others - 2 430 Total 60 194 8.790 "Average of cores d-1, top 35 mm (Bush, 1966, p. 64) *Macrostomum sp. following wave. The subterranean cur- rent, therefore, will mix more and more with oil which will invade biotopes far from the contaminated surface. On the positive side, the large surface area of the interstitial oil droplets will facilitate bacterial degradation. Some quantitative samples of sand which we collected came from a small beach in the mangrove, approximately 2 km southeast from the Galeta Station. The sand (medium grain size, with a high amount of detritus), taken at midwater level, was heavily contaminated with oil to at least 30 cm sediment depth. An analysis' showed that 100 cm of sand (average wet weight = 121.9 g) held 31.8 g of water and 6.2 g oil. One fresh sample was brought back to the laboratory and studied alive, using the magnesium chlo- ride technique described by Sterrer (1968). Data for comparison with unaffected beach sediments of similar characters come from Bush (1966), who did her study on Florida beaches, and from unpub- lished samples collected in Morehead City, North Carolina, during a recent stu- 'To determine the oil content of the samples, the sand was dried at 37 C over silica gel until no more weight loss occurred. Then it was repeatedly washed in benzene. The blackish stained benzene was then evaporated in large Petri dishes at 37 C and the residue weighed. Fig. 5. Intertidal stilt roots of Rhizophora in a badly affected mangrove area. dent excursion with Dr. R. Riedl (Chapel Hill). Whereas the Florida data seem to refer to a medium sheltered beach, the North Carolina material was collected on a very sheltered tidal sand flat. For better comparison, the number of specimens given in Table I have been calculated for 100 cm3 of sediment. The considerable difference in the nem- atode figures of the Florida and the North Carolina samples can be explained partly by the much more sheltered position of the latter collecting locality. This invari- ably means, on sandy beaches, that the absolute numbers as well as the domi- nance of nematodes increase. Another factor is that of the method-our samples from both Panama and North Carolina were washed with about 8 liters of mag- nesium chloride solution and then filtered through a plankton netting of 65 micron mesh width, whereas the Florida samples were treated with much less fluid and simply decanted. Summarizing these few and very pre- liminary data, it seems that the oil inflow into the sand beach ecosystem results in a dramatic reduction of the meiofauna population. Obviously, animals with a relatively large (limbs) and inert (cuti- cula) body surface, such as crustaceans, are the first to disappear. The occurrence of comparatively large amounts of small ciliates might indicate the presence of oil- degrading bacteria on which they prey. Mangroves As could have been expected, the man- groves, being a predominantly intertidal community, suffered the most under the oil spillage. All the oil that could not settle along the exposed rocky shores was finally driven into the protected mangrove area (Fig. 5). The wide intertidal mud flats February 15, 1970 223 were all more or less thickly covered with oil. So was the surface of the tide channels distant from the open sea. Every footstep on the mud at low tide released large quantities of oil from the substrate. The pneumatophores of black mangrove trees (Avicennia) were all covered with a mix- ture of oil and mud. The stilt roots of the red mangrove (Rhizophora) had a thick Fig. 6. Dead oil-covered seedlings of Rhizo- phora. layer of pure oil on their mesolittoral sec- tions. It is still too early to judge damage on the fully grown trees, but it is to be expected that A vicennia in particular will suffer, since their pneumatophores are of vital importance for the ventilation of the remainder of the root system, which is buried in the anaerobic mud. The major- ity of young seedlings of Rhizophora were found to be killed, covered by oil (Fig. 6). We did not obtain any data on the microfauna of the mud which could not be studied alive. A strong reduction of the fiddler crab population (Uca sp.) could be observed in comparison to other man- grove areas. This is not surprising if we compare the oil content values of four mud samples taken in a mangrove swamp 1 km southeast of Galeta Marine Station, 500 m distant from the open water. The samples (5 cm surface layer) were selec- ted from intertidal localities which ap- peared to be affected by a various degree (I-III): Wet weight (g/100 cm3) Water Oil Sample (saturated with water) (g/100 cm3) (g/100 cm3) I 170.3 56.1 9.3 II 143.1 53.4 17.0 III 119.2 50.9 21.4 Fig. 7. Oil-smeared bostrychietum on Rhizo- phora roots. The characteristic intertidal algal com- munity "bostrychietum" on the Rhizo- phora stilt roots and its inhabiting micro- fauna were practically eliminated in all oil exposed areas (Fig. 7); as were the sedentary animals of this zone, such as oysters (Crassostrea sp., Fig. 8), mussels (Brachidontes sp.), barnacles (Balanus sp.), sponges, tunicates, and bryozoans (compare: Riitzler, 1969). The infralittoral horizon in the man- groves consists of numerous tide chan- nels and lagoons. There the wickerwork of Rhizophora stilt roots provides protec- Fig. 8. Dead oil-covered oysters on Rhizophora stilt roots. tion for many juvenile and adult fishes and various crustaceans, many of which are of commercial importance. All of these are directly or indirectly (via the food chain) endangered by oil pollution. Ob- viously affected are those species which, for respiration, or for obtaining food, have to penetrate the air-water interface. We have observed dead and dying young sea turtles (Caretta sp.) on mangrove beaches; mass mortality of seabirds had been reported by the Torrey Canyon Report; a number of oil-smeared herons and one dying commorant were ob- served by a staff member of the Smith- sonian Tropical Research Institute, near Galeta. Conclusions This fragmentary survey taught us the importance of immediate research on the effects of oil pollution in the sea, so that we may be ready for possible future oil spills; with increasing use of larger tankers, wrecks in the future could be catastrophic. Even some of the long-term effects of the fortunately moderate accident off Galeta have yet to be investigated. We should take advantage of this warning and concentrate on research at places, such as Galeta, where the conditions of the natural environment can be studied, as well as the effect upon those conditions of experimentally introduced oil spills. Physical and chemical as well as biologi- cal phenomena must be studied in this connection. STRI has already proposed one such effort. Acknowledgment We are grateful to Dr. P. Glynn, Mr. E. Kohn, and Dr. I. Rubinoff of the Smith- sonian Tropical Research Institute for their hospitality and valuable advice. Dr. Rubinoff provided Figures 1, 2, and 4. References Bush, L. 1966. Distribution of sand fauna in beaches at Miami, Florida. Bull. Mar. Sci., 16: 58-75. Riitzler, K. 1969. The Mangrove Community, Aspects of its Structure, Faunistics and Ecol- ogy. Proc. International Symposium on Coastal Lagoons, Mexico City, 1967 (in press). Sterrer, W. 1965. Zur Oekologie der Turbel- larien eines suedfinnischen Sandstrandes. Botanica Gothoburgensia, 3: 211-219. 1968. Beitraege zur Kenntnis der Gnathostomulida. I. Anatomie und Mor- phologie des Genus Pterognathia Sterrer. Arch. Zool., 22: 1-125. 224 BioScience Vol. 20 No. 4