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APPENDIX A Impact of Some Major Spills (Spill Case Histories) INTRODUCT ION Both acute spills and oil seeps have provided oppor "unities for field study of the impact of oil on the surrounding marine ecosystems. Popularly, they are thought to resemble each other rather closely, and indeed it is often assumed that the natural oil seep provides the sort of controlled experimental situation for field studies that cannot be found with the unpredictable acute tanker spills. Scientific studies of tanker spills present several problems for the serious scientist--awesome difficulties in field sampling, and readiness of personnel and equipment. Spills are not anticipated, and in the past, personnel and equipment have seldom been readily available. Also, most spills occur in areas that have not been studied previously, and adequate controls are rare. Spills frequently occur in weather conditions that make sampling difficult or impossible. These problems are compounded in offshore spills, where sampling becomes much more difficult, background data are less available, and the expense of large ship operations is difficult to finance on short notice. Despite these difficulties, it is encouraging that acute spills have not only continued to receive scientific attention since the writing of the last NRC report, but also that field studies have increased in number and in scope and have yielded some valuable data. The long term follow-up studies have provided further understanding, both of the vulnerability of the various ecosystems and of the biological recovery processes. Natural oil seeps, on the other hand, have received much less attention, despite their seemingly obvious availability as a natural experimental spill situation. Geographically, these sites are not easily accessible, generally located in unsettled offshore locations, and removed from marine laboratories. The major exception to this, the seep off southern California, is located near a heavily populated area with several major marine laboratories, and indeed has been the subject of a number of studies. More recently, work has been initiated on two seeps off the east Baffin Island coast in the Canadian Arctic. In this case the seeps lie in an area of considerable geological interest, and on the cruise track of annual Arctic research cruises out of eastern Canada. 549

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550 However, seeps differ in several aspects from tanker spills and from well blowouts as to the chemical composition of the oil fraction accomodated in the water and the generally lower rate of release and local concentration. Seeps therefore are not truly analogous to con- trolled tanker spills, but they do provide an opportunity to obtain parallel observations, par ticular ly on the weather ing processes of oil and on the impact of such aged oil on surrounding biota under chronic conditions . Only a few major oil spills have been the object of detailed scientific study, but among these are two of the largest that have ever occurred--the Ixtoc I blowout of June 9, 1979, in the Gulf of Campeche, Mexico, and the breakup of the tanker Amoco Cadiz of f the coast of Brittany, France, on March 16, 1978. In addition to these giants there are a number of smaller spills that have received considerable scien- tific attention--the Florida sp'11 in Buzzards Bay, Massachusetts (1969), the Arrow spill in Chedabucto Bay, Nova Scotia (1970), the Metula spill in the Strait of Magellan {1974 ), the Argo Merchant breakup off the east coast of the United States (1976), the Tsesis in the Baltic south of Stockholm (1977 ), and the Kurdistan in Cabot-Strait off Nova Scotia (1979~. The first spill to receive serious scientific attention, the Torrey Canyon off the south coast of England (1967), remains of interest to this date. However, the heavy use of disper- sants and other chemical and physical treatment agents places this spill in a separate category, and many of the impacts observed were due largely to the awesome cleanup e f for ts used and not to the spilled oil. A considerable amount of information on both the behavior and the fate of the spilled oil in the mar ine environment and on the impact on the living resources has been der ived through these studies . However, all these spills dif fer both in the fate of the oil and in their bio- logical impacts, with each spill presenting yet another set of condi- tions and facets of petroleum efforts in the oceans. The examples descr ibed below demonstrate this var. lability and dissimilar ity, but a t the same time they indicate some coupon features. AN INSHORE SPILL: THE BARGE FLORIDA Two spills in relatively protected waters were intensively studied for many years: the Florida barge spill of 1969 (Sanders et al., 1972, 1980) in the West Falmouth area of Buzzards Bay, Massachusetts, and the Arrow spill of 1970 in Chedabucto Bay, Nova Scotia. The barge Flor Ida grounded on rocks off West Falmouth Harbor, ~- Buzzards Bay, Massachusetts, and lost 630 tons of No. 2 fuel oil. A storm the following day drove the oil ashore, mixing it into water and sediments . There were immediate k ills of small fishes, benthic inver- tebrates, and marsh organisms . Some dispersants were used, and booms were deployed in an attempt to keep the oil out of West Falmouth and Wild Harbor . Visible oil never appeared in West Falmouth, but the booms were unable to keep oil out of Wild Harbor. The extent of the immediate k ill was documented by t imely sampl ing befor e the dead

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551 organisms decomposed. Oil and its effects persisted for at least 10 years after the spill (Sanders et al., 1980) . Oil Fate The slick was washed ashore and mixed into the water rapidly. There were no special studies of any effects that the intact slick might have had in the short period before its breakup. No concentration measure- ments were made on oil in the water column. In the sediments the spilled oil fared rather differently, with recognizable components of the spilled No. 2 fuel oil persisting for at least 8 years. Sediments from the Wild Harbor station yielded 1-3 mg aromatic fraction per gram of dry weight until at least July 1976, compared with 0.02-0.04 mg/g for control stations (Teal et al., 1978) . Impac t on Bio ta Fish An immediate f ish k ill was documented at the time of the spill, with fish washed ashore in windrows (Sampson and Sanders, 1969~. Measure- ments on the mixed function oxygenase (MEtO) system in Eundulus heteroclitus from Wild Harbor revealed induction, i.e., enhanced levels of the activity of this hydrocarbon-metabolizing enzyme system, in comparison with similar fish taken from control stations (Burns, 1976). Four years after the spill, the fish showed a reduction of body burden of hydrocarbons to near background levels, presumed to be the r esult of the LEO enzyme activity (Burns and Teal, 1979) . High MEG levels continued to be measured 8 years after the spill in F. heteroclitus from this area, correlating with the persistence of oil in the sediments (Stegeman, 1978 ~ . Benthos The most persistent impact was in the benthic macrofaunal communities (Sanders, 1978) . Within 48 hours after the arrival of the oil from the Florida, there was nearly total eradication of the macrobenthos at the most heavily oiled sites, with oil concentrations exceeding 133 ng/g wet weight (ca. 400 ug/g dry weight). At sites with intermediate oil levels (9-100 ug/g), there were intermediate reductions as compared with control s ites . Soft-bodied animals k illed by the oil disappeared within 1 week. The deaths would not have been detectable if sampling had been initiated later than a few days after the spill (Sanders et al., 1980~. Ampeliscid amphipods were particularly vulnerable to oil, in par t because of the habit of these organisms to move into contami- nated sediments. These declines In the macrobenthos continued until the oil had decreased sufficiently in concentration and toxic components to permit their survival (Sanders et al., 19721.

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552 Oppor tun is t spec ies typi ~ fed by Capi tella in the inshor e s tation 5 increased greatly in abundance, monopoliz ing the otherwise defaunated sediments for the f irst 11 months following the spill . At that time this opportunistic species peaked in population, and subsequently "crashed. n A similar course was observed with another opportunistic species Mediomastis in sites further offshore, i.e., steady increase in population numbers while overwhelming the defaunated area, followed by a rapid crash, or drop in numbers. It differed from Capitella only in that it peaked somewhat later and its opportunistic period occurred for several months later. In general the changes in fauna matched the extent of pollution by the No. 2 fuel oil, both in intensity and duration (Sanders et al., 1980). Faunal changes included decreases in diversity, in density, and in numbers of species. The recovery pattern of the impacted communities also showed abnormalities that could be linked to the extent of oiling. For example, at the minimally oiled sites the recovery process was rapid with short term effects. Recovery was essentially complete within a year after the spill. However, at the intermediate and heavily oiled sites the recovery process was markedly different. At the intermediate polluted sites the recovery process was dominated by the initial deaunation and subsequent high postlarval settlment thalf million/ cm~2), leading to high numbers of individuals (high richness) but low numbers of species (low evenness). Here a more normal recovery pattern was not evident until 3 years after the spill. At the most heavily oiled sites a "normal" recovery pattern was not evident for the 52 months of study following the spill (Sanders, 1978; Sanders et al. , 1980). There were no detailed meiofaunal studies, although in some of the initial samples taken in the most heavily oiled stations, field notes showed the presence of large numbers of nematodes. Intertidal Communities Marsh grass (Spartina alterniflora) was completely killed off on the most heavily oiled parts of the intertidal area (oil concentrations over 2,000 ng/g). By 1981 recovery was not yet complete, although most areas seemed normal in appearance at first visual inspection. Bivalves were particularly susceptible to the oil and its effects. Approximately 77 bushels of soft-shell clams (Mya arenar ia) and 11, 200 bushels of seed clams were reported killed in Wild Harbor (Sousa, 1970~. Fiddler crabs (Uca pugnax) were reduced in density in the oiled marsh, which, as in the case with the benthic amphipods, acted as a lethal trap for these territorial organisms. Behavioral changes caused by the oil included slowing of movements and digging of burrows, the latter being shallower than normal. Newly settled animals appeared to be more susceptible to the oil than the adults, and their settling success was sharply reduced (Krebs and Burns, 19771. Recovery was found to be highly correlated with the loss of the naphthalene fraction of the oil trapped in the sediments. However, recovery of the fiddler crab population was not complete in 1977, 7 years after the spill

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553 (Krebs and Burns, 19771. Induction of MFO system activity was detected in tissues of the fiddler crabs, but it would seem that the MEN levels were insufficient to deal with the body burden of hydrocarbons within the lifetime of these organisms (Burns, 1976) . Changes in populations, similar to those descr ibed for the inter- t idal areas, were found in the soft-bottom inter tidal areas below the salt marsh (Sanders et al ., 1980) (Figure A-1 ~ . AN OPEN BAY SPILL: THE ARROW The Arrow spill (Anon, 1970 ~ occurred on February 4, 1970, in Chedabucto Bay, Nova Scotia, when the tanker ran aground on Cerberus Rock on her way into the off-loading facilities in the Strait of Canso. She was carrying 15,000 tons of Bunker C fuel oil, of which about two-thirds were released into the waters of the bay (Anon, 1970 ~ . Although Chedabucto Bay in some ways represents a relatively sheltered environment (its northern half consists of numerous small lagoons and shallow embayments), the entrance to the bay opens directly onto the Atlantic Ocean, and at the time of the accident the prevailing winds caused high sea state conditions within the bay. As a result, oil driven by wind (Figure A-2) and wave action coated over 300 km of the bay's shorelines (Figure A-3), before the remainder of the oil was swept out of the bay and into the Atlantic. Eventually oil from the Arrow was traced as far south as Halifax, N. S., and Bermuda. Oil Fate In May 1970, 3 months after the spill, levels as h igb as 100 ug/L were found in the water column (Levy, 19711; but by April 1971, concentrations had dropped to background levels, cat 1 1lg/L (Gordon and Michalik, 1971~. Oiling along the southern and western shores of the bay resulted in a mixture of oil with sand, gravel, and rocks to yield a resistant pavement of tar along much of the coastline. By 1976 such surface oiling was sharply reduced, either by wave erosion or by burial, and could be found v isually pr imar fly in a few "hotshots " (Janus in Lagoon, Inhabitants Bay, Black Duck Cove) (Vandermealen, 1977) (Figure A-4) . However, a parallel chemical analysis of subsurface sediments indicated high concentrations of Arrow oil persisting below the surface within the beaches (1, 280 fig Bunker C per gram of sediment at 7-11 cm, compared with 106 at the surface and 27 ~g/g at 12-15 cm), represent- ing a potential long term source of reentry of spilled oil (Figure A-5) (Keizer et al., 1978) . But by this time, the origins of these hydro- carbons could no longer be unequivocally traced to the Arrow because of weather ing and contamination from subsequent spills (Keizer et al., 1978) .

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554 100 ALSO 40 30 . 20 10 . - 5 4 ) _ ~ , 3 2 _ Whole found Stations 9,'0,20.3~.3s and ISt Intertidal Discrepancy index values for the first and second years Sta. 9 Sta.= Intertidal ~ sta.Io Sta. 3' a Sta. 20 a Sta. AS ~ savor 30- ~ ~\'/ - ~ e - . l_/ ~ .'L ~ ~ fovea _5 \ 8L'ZZAnOS Bar 35 ~ _ <=~ '-- ~20. , ~\ 'J ~ At, , ~ 1 o~ OCR for page 549
555 '''l.'l WIND SPEED 0 3060 KNOTS ~ 1ll//1ll 1 /11\\\\\~\ \\~7~ ~ 3 1 4 1 - 5 6 1 j 1 8 1 9 1 10 1 11 12 FEBRUARY Tl M E ( DAYS ) FIGURE A-2 Mean wind vectors over Chedabucto Bay, February 3-12, 1970. Shown are the 6-hourly mean vectors of the reduced geostrophic winds . SOURCE: Based on data from Anon (1970~. Impact on Biota Most of the work on organisms was done on littoral communities, with very few observations made in the water column. Thus, for example, no data of impact on f ish are available . Conover (1971 ) found incorporation of oil droplets by copepods in the bay water column. Most apparently passed through the animals without modification, although no detailed uptake or tissue hydrocarbon studies were done at the time. The oil droplets, many of the general size range of the food of the copepods, were apparently filtered from the water column by the animals. Eventually a considerable portion of the oil droplets became associated with the fecal pellets. AS much as 10% of the oil in the water was associated with the copepods, and up to 7% was found in the fecal pellets, sugggesting that this route may be an important sedimentation route for spilled oil. There appeared to be no obvious effect of the oil on the copepods, although no data are available on th is . Benthos Most studies on benthic organisms were carried out in the rocky and sedimentary intertidal areas (Thomas, 1973 , 1977 , 1978), although in follow-up studies, attention was focused on the low energy, silt- dominated lagoons. The oil was concentrated primarily in the upper two-thirds of the intertidal zone. Studies showed the oil to be most persistent when stranded along the mean high tide line, where in sheltered lagoons it was still present visually 10 years after the evens e The rockweed Eucus vesiculosus was reduced in vertical distr ibution for about 5 years. FOCUS spiralis, which is confined generally to the region up to the high tide line, was killed off completely and had not reappeared in the oiled region by 1976, 6 years after the spill. In sheltered areas the marsh grass Spartina

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556 [ 'W:. ~ All-r | . STRAIT: .\ it: . OF CANSO : ~MADAM: . .:! SCOTI A :3 . . 2 . :-~ NOVA to CERB ERUS . ~in- ROCK CHEDA BUC TO BA Y -W. : ATLANTIC OCEA N FIGURE A-3 Geographical extent of shoreline contamination in Chedabucto Bay, February 1970, immediately following Arrow breakup. SOURCE:: From Anon (1970 ~ . alterniflora population declined steadily after the spill, with few surviving plants remaining 1 year later, However, it recovered 2 years later , by 1973. Rocky shore animals including barnac' es and per i- winkles did not change in abundance or in distribution except where their habitat had been altered by changes in the rockweed, demonstrat- ing the significance of community associations (Thomas, 19781. Larvae of the common barnacle Balanus balanoides apparently settled and grew normally, even during the spill year, 1970 (Thomas, 1977~. In contrast, follow-up studies suggested changes in bivalve larval recruitment 6 years afterward (Gilfillan and Vandermoulen, 1978~. A detailed follow-up study was done in 1976, 6 years after the spill, when sediments from oiled sites still contained 10-25,000 ug/g of oil (measured with fluorescence). Species diversity (Shannon-Weiner index) was lower at oiled than at unoiled control sites. Macrofaunal biomass was cat 1,400 wet g/m2 at oiled sites, versus approximately 4,400 wet g/m2 at control stations. Oil concentrations in living clams in 1976 averaged between 150 and 350 ug/g, compared with 650 g/g in recently dead bivalves in 1970. Periwinkles also were found to be contaminated with oil, but the average level of contamination was only 12-18 ug/g. The marsh grass S. alterniflora from six oiled

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o75 In ._ 50 ~ _ \ _ ~ 25 o To o \ \ 557 to \ total oil cover `` `_~i ~ ~-_hea\,y oiling only . , , , , , -^_, '70 '71 '72 '73 '74 '75 '76 '77 Time ( years ) FIGURE A-4 Erosion pattern of stranded Arrow Bunker C fuel oil on Chedabucto Bay shorelines, 1970-1976. Curves based on shoreline surveys and visual inspection of res idual stranded oil . SOURCE: Vandermealen (19771. sites still showed surprisingly high contamination of about 15,000 ug/g, compared with less than 70 in control (Thomas, 1978~. Six and seven year s after the spill, populations of soft-shelled clams from oiled sites were still stressed (Gilfillan and Vandermealen, 1978~. Fewer mature adults were found at oiled stations. Individuals showed lower shell growth, lower assimilation rates, and lags of 1-2 year s in tissue growth . These observations wer e con f irmed in par allel studies by Thomas (1978), and reduced weight of body and shell persisted through 1979 (MacDonald and Thomas, 1982) . On the other hand, populations of the lugworm Arenicola were more abundant in oiled sediments in 1976 than anywhere else in Nova Scotia. They did exhibit elevated hydrocarbon concentrations, suggesting that they are relatively resistant to oil pollution (Gordon et al., 1978~. AN OPEN OCEAN SPILL WITH OFFSHORE WINDS: THE ~~ ~C~-^ The Argo Merchant spill (Grose and Mattson, 1977; Wilson et al., 1978), in several ways, represents the opposite to the Arrow spill. Both spills occurred in winter, on the northeast coast of North America, with the same oil cargo (Bunker C fuel oil) . However, whereas the Arrow broke up in a large embayment, with initially onshore winds, the Argo Merchant ran aground and broke up in open waters, with prevailing offshore winds for most of the spill period. In the end, much of the

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558 | E3unker C oil | O'er 60 ~ 4` ~\~ AJAR trapped oil Tidal flushing ~ Water column ( p9/1) ``o 4) ( H9/1) .~ /~6 FIGURE A-5 Summary of stranded Bunker C fuel oil reentry pattern into mar ine environment by oil stranded on low energy gravel-cobble beach . SOURCE: Vandermeulen and Gordon (1976 ~ . Arrow' s cargo became stranded on ad jacent coastlines, while the oil from the Argo Merchant disappeared from view in the Atlantic Ocean. The Argo Merchant ran aground on Nantucket Shoals, off Massachu- setts, on December 15 , 1976 (Figure A-6), and over the next month spilled almost her entire cargo (29,000 tons) of No. 6 fuel oil (Grose and Mattson, 1977 ~ . The cargo also contained about 20 Be of its volume in cutting stock {equivalent to No. 2 fuel oil) for thinning purposes. Storms broke up the vessel after grounding, and attempts to pump the oil into another vessel failed. Burning the oil was tr fed without success. No dispersants were used. Oil escaped from the wreck for 1 month after grounding, but sur- prisingly little oil was found later in its immediate vicinity. In February 1977, significant contamination was found near the wreck, extending at least down to 8- to 13-cm depth, but by July 1977 no evident cargo oil remained. It is speculated that the bow forced oil into the sand, or that sand was forced age inst the hull by currents and carr fed the oil away from the wreck along the bottom. Most of the oil that appeared on the sur face was formed into large floating pancakes n and disappeared into the ocean to the east (Figure A-6~. Parts of the cutting stock dissolved and could be detected under the slick at concentrations up to 250 ,~g/L. It was the occasion for one of the most elaborate slick monitor ing efforts up to that time (e.g., Grose and Mattson, 1977; Spaulding, 19781, but because of the bad weather, relatively few samples of water, sediment, or biota were obtained (Grose and Mattson, 1977; Wilson et al., 1978) . Despite the relatively high potential toxicity of the cutting stock in the cargo, there was little evidence of impact on the mar ine fauna or phytoplankton . The accident occurred at the time when the fewest potential effects on pelagic organisms would be expected: a period of low productivity in the water column, with few fish eggs and larvae present. The spill did provide, however, the first indications

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4i 40. 41 40 41 40. 559 Too - 69 68 CAPE COD : . ,:, NANTUCKET ISLAND ~ . at. C~y 90-100 % ATLANTI C r ,200m ~ _s J:20Om ,)2000 m ~r 70. 6g 68. 70- 69~ . , _ _ . , . , _ , NANTUCKET ISLAND a. 0! 96-100 ATLANTIC 200 m :~J ~ooo m 69 76~,~20,0m CAPE COQ NANTUCKET ISLAND ~ '=3 4lo 40 41 40 67- l Pancakes / \ Rainbow /~9Rt i~ncokes / Poncakes ~ ~ / / Light / Poncakes / 10-20% k~7~7 907; >~ Z. s ATLANTI C Heavy Pancakes n ~V/O J~ 20-30% ]~ J Rainbow Pancokes '<10% _,~,,, Pancakes , ~ =e, ~ 200 m :20Joo~ 1 . . _ l Y _ 71- 70- 6g. 68- 67 41 g40 FIGURE A-6 Hor izontal dispersion of oil spilled from the Argo Merchant, December 17, 20, and 23, 1977. SOURCE: Lissauer and Welsh (1978~.

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572 Intertidal and Subtidal Communities The macroinfauna, along the Texas coast, dominated by polychaetes and haustoriid amphipods, showed decreases in population density but not a parallel decrease in numbers of species. The changes may have been due to the Ixtoc I oil, but hurricanes, seasonal changes, and cleanup tech- niques (dispersants) may also have been responsible (Tbobeau et al., 1981~. However, it should be noted that other studies in the Gulf region do not show any effect of storms on these organisms. AN ONSHORE l'ROPICAL SPILL: THE ZOE COLOCOTRON I The Zoe Colocotroni (Nadeau and Bergquist, 1977; Tosterson, 1977) spill represents one of the few tropical spills that has received any scientific attention. As a result, little is known about the potential impact of oil on tropical ecosystems, especially the common mangrove and coral reef communities, which constitute a large part of the tropical marine coastline. The tanker Zoe Colocotroni ran aground off LaParguera, Puerto Rico, on 18 March 1973. In order to free the vessel, about 5,000 tons of crude oil were pumped overboard. An estimated 60% of this crude oil was subsequently swept into Bahia Sucia, off the extreme southwestern tip of Puerto Rico. There the oil impacted the sea grass beds, mangrove communities, and lagoons. Oil Fate Four years later (1977) much of the oil had disappeared, but some still remained on the west side of Bahia Sucia. Analyses showed this to be highly weathered (Page et al., 1979~. Follow-up work, in 1978 and 1979, showed that Zoe Colocotroni oil, apparently unaltered, still persisted in some areas. Tarry residues were found in the bottom ooze of largely shallow salt lagoons. Droplets of tar were readily dislodged when the soft bottom sediments were disturbed. Once on the surface of the lagoon water these tar droplets slowly formed sheens of oil . As ide from such tarry deposits, however, it appears that most of the stranded Zoe Colocotroni oil had undergone extensive weathering. Analyses of oil sediments from all impacted environments showed extensive degradation of the lower-molecular-weight hydrocarbons, presumably because of high microbial activity. Leaching out of soluble alkanes and of the smaller aromatic components by tidal waters may also be a factor in these environments (Gilfillan, personal communication) . Impact on Biota An initial assessment of the impact of the Zoe Colocotron i on biological communities of the area showed large numbers of dead sea cucumbers, conchs, prawns, sea urchi ns, and polychaete annelids washed

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573 ashore (Nadeau and Bergquist, 1977)0 Dead and dying organisms were also found in offshore sea grass beds (Thalassia). The sea grass beds themselves also suffered from contact with the oil entrained into the water column by the action of the surf. Leaves turned brown and black, and a considerable amount of Thalassia died and was removed by wave action. The oil also had an acute effect on the mangrove communities, with the red mangrove most severely affected, together with the fauna 1 iving in the mangrove prop root environments . Subsequen t surveys of the impacted area have shown marked changes in the affected faunal and floral communities. By 1976 about 1 ha of red mangroves had become defoliated and eventually died, presumably through suffocation of the specialized aer ial prop roots by oil . Apparently, however, degradation of spilled, stranded oil in tropical environments occurs at a greater rate than in more temperate climates, as suggested by chemical analyses of oil from the Bahia Sucia sediments. A similar rate of biological recovery appears to be occurring, except for the impacted red mangrove conununities in which, at the time of the most recent survey (1979), the faunal composition was still marked by the presence of opportunistic polychaete species (Gilf illan et al., 1981) . In general, changes in faunal composition appeared to be related to the degree of weather ing of oil, which ire turn is related to water movement over the sediments. SUMMARY AND DISCUSSION Clearly, these spills differed markedly in their extent and impact, much being dependent on meteorological conditions operating at the time of the spill . Thus, for example, the Arrow' s spilled oil eventually washed out into the open Atlantic, but not before all of the Chedabucto Bay coastline had been heavily oiled under the influence of prevailing easterlies and southeasterlies. The coastline of Massachusetts escaped this fate 6 years later when the Argo Merchant ran aground on the Nantucket Shoal, largely because of offshore winds operating for most of the postspill per iod. On the other hand, Amoco Cadiz oil remained near the Brittany coast for several weeks under the action of the shifting northeasterly and northwesterly winds. The IXtoc I blowout presented problems of a prolonged underwater oil spill source into a large coastal circulation system. The Zoe Colocotroni spill in general parallels the Flor Ida spill in its impact on benthic communities and in long term oiling of soft lagoon al sediments. Its differences lie pr imar fly in the higher temperatures found in the tropical environment, which appear to hasten the breakdown of spilled oil. Or the other hand, the Zoe Colocotroni presented two new features of oil spills: oiling of sea grass beds and impact on mangrove communities. Biological impacts var. fed as did the oil fates, from the long term problems still encountered in benthic communities at the Florida site to the virtual absence of observed effects on biota from the Ixtoc I, although the latter in large part reflects the absence of biological studies. Low energy coastal environments appear to be particularly vulnerable to the effects of oil and to oil entrapment, as was seen at

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574 the Florida, Arrow, Zoe Colocotroni, and Amoco Cadiz spills. They also demonstrate the persistence of both the oil and its effects, especially in association with soft sediments (see also Teal and Howarth, 1983), in some instances for over a decade (Arrow, Flor ida) . However, as noted elsewhere in this report, oiled environments do clean themselves, and there appear to exist in all cases briefly examined here, mechanisms of oil degradation and biological recovery with the potential for eventual complete recovery. If one were to rank the various factors that can influence the potential impact and persistence of oil in these various spills, then clearly, biological impact is linked closely to the extent and duration of oiling (e.g., Florida, Amoco Cadiz). In this respect, the low energy lagoonal environments appear to be most susceptible for long term impact. Another, generally unexplored, factor seems to be the rate of release of spilled oil, with the rate of oil spillage being related to spill impact. For example, the Amoco Cadiz spilled approximately 100,000 tons over 1-2 days, while the Ixtoc I blowout spilled about the same amount in about 2 months. Tne Santa Bar oar a Channel seep, on the other hand, released about that amount over the course of a century or more. While there are, of-course, many differences between these three spills, one would expect qualitative differences in their impact, just because of the different release rates. Together these five examples of tanker spills have introduced about 270,000 tons of crude, Bunker C, and No. 2 fuel oils into the world's oceans, plus at least twice that amount from the Ixtoc I blowout (estimated variously at between 454,000 and 1,400,000 tons). Remnants of this oil can still be found in five out of the six (the Argo Merchant's cargo disappeared from view totally). Remnants of their effects can also Still be measured, in terms of numbers of biota and in depression of certain metabolic parameters, at the sites of the Florida, Arrow, Zoe Colocotroni, and the Amoco Cadiz, and perhaps at the IXtoc ~ . , I. Of these, the impact on seabird populations at the Amoco Cadiz site has undeniably been the most dramatic. A disastrous effect on the bird population had been feared in the case of the Amoco Cadiz, but it did not materialize, suggesting that the survival potential of seabirds, at least for the eastern North Atlantic populations, is quite good (see also Chapter 5, Impact on Seabird Populations section). In none of these examples has a widespread, immediate impact on fish populations been observed, nor generally on the pelagic plankton communities. By far the most persistent impact is found instead in the intertidal and subtidal benthic communities, where long term perturbations can be found several years after the spill. Where the oil has become stranded on coastlines, such impact can extend to the ecological balance and stability of the coastlines as well as to economic resources, as in the case of the impacted oyster mariculture of northern Brittany (Amoco Cadiz, Maurin, 19811. One major feature of oil spills, which has not received much attention and remains an enigma, is the fate of nonstranded oil. Of the volume of oil spilled by the tankers discussed here, about 165,000 tons (60~) did not come ashore but is largely unaccounted for, having

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575 TABLE A-1 Estimates of the Distr ibution of Oil Spilled from the Tanker s Ar row, Zoe Colocotron i, and the Amoco Cadiz ~. . Tanker Distr ibution Tons Percentage , Arrow" In tanker pr for to casualty Removed by pumping Remaining in hull 15,000 5,432 168 Ashore in Chedabucto Bay1,895 At the surface within Chedabucto Bay21 At depth with in Chedabucto Bay? Evaporated? Swept ou t into the Atlantic 8,421 Zoe Colocotronib Pumped overboard5, 000 Ashore in Bahia Sucia3,00060 At sea/evaporated2, 00040 Amoco CadizC Total spilled223,000 - Subtidal sediments18,0008 Onshore62, 00028 Water column30,00013.5 Biodegraded10,0004.5 Evaporated67 ,00030 Unaccounted for 46,000 20.5 Canon (1970 ~ . tNadeau and Bergquist (1977~. undlach et al . (1983 ~ . either evaporated into the atmosphere or dispersed or dissolved into the water column. In addition, most of the spilled oil from the Ixtoc I blowout remains either at sea or in the atmosphere. Little can be said about this signif i cant portion of the spilled tonnage, for there exist at present no data to enable us to assess either its fate or its degradation rate in the open ocean. The largest gap in ache data to date. Estimates made at the time of the Arrow spill were at best crude (Table A-1), but they have not been refined significantly, and no estimates exist for the Florida, Argo Merchant or Ixtoc I. For the Zoe Colocotroni . only the s imulest ~, _ _ _ absence of a spill budget (mass balance ~ is probably the s ingle estimate exists for oil lost into the water column, 40% (Nadeau and Bergquist, 1977) . The best attempt at an oil budget available is probably that calculated for the Amoco Cadiz (Table A-1) . However, even these figures, based in part on chemical analyses and in part on theoretical extrapolations, remain estimates at best.

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576 As a large por tion of the oil spilled to date, whether from tanker s or from other discharges, appears never to have reached shorelines (where amounts and effects can be assessed to some extent), the fate, and ultimate impact of the oil presents a large set of questions to be answered . REFERENCES Aminot , A., and R. Kerouel . 1978 . Premier s resultats sur 1-hydrolog ie , 1 'oxygene dissous et les pigments photosynthetiques en Manch Occidentale apres 1 'echouage de 1 'Amoco Cadiz, pp . 51-68 . In Conan e t al ., eds. Amoco Cadiz: Consequences d 'une pollution . accidentelle par les hydrocarbures . CNEXO, Par is . Anon. 1970. Report of the Task Force--Operation Oil (Cleanup of the Arrow oil spill in Chedabucto Bay). Vols. I, II, III, IV. Canadian Min ister of Transpor t. Atlas, R. M., G. E. Roubal, A. Bronner, and T. R. Haines . 1982 . Biodegradation of hydrocarbons in mousse from the Ixtoc ~ wel 1 bl owout. Amer ican Chemical Society, Washington, D. C. ~ in press ~ . Atwood, D.K., convener. 1980. Proceedings, Symposium on Preliminary Scientific Results From the Researcher/Pierce Cruise to the Ixtoc I . Blowout. U.S. Department of Co~unerce, National Oceanic and Atmospher ic Administration , Boulder, Colo. 591 pp. Atwood , D. K., J . A . Ben jamin, and J.W. Farrington. 1980. The mission of the September 1979 Researcher/Pierce Ixtoc I cruise and the . . physical situation encountered. In Proceedings of a Symposium on Preliminary Scientific Results From the Researcher/Pierce ~xtoc I Cruise. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Office of Marine Pollution Assessment, Washington, D. C. Boehm, P., A.D. Wait, D.L. Fiest, and D. Pilson. 1982. Chemical assessment-hydrocarbon analyses, Section 2. Ixtoc Oil Spill Assessment Final Report. Contract AA851-CTO-71. Bureau of Land Management, U.S. Department of Interior, Washington, D.C. Brooks, J.M., B.B. Bernard, T.C. Saner, Jr., and H.A. Reheim. 1978. Environmental aspects of a well blowout in the Gulf of Mexico. Environ. Sci . Technol . 12: 695-703 . Burns, K.A. 1976b. Microsomal mixed function oxidases in an estuar ine f ish, Fundulus heteroclitus, and their induction as a result of environmental contamination. Comp. Biochem. Physiol . 53B: 443-446 . Burns, K.A., and J.M. Teal. 1979. The West Falmouth oil spill; hydrocarbons in the saltmarsh ecosystem. Estuarine Coastal Mar. Sci . 8: 349-360 . Cabioch , L., J . C. Dauvin , J . Mora Bermudez , and C . Rodr iguez Babio . 1980. Effets de la maree noire de l' Amoco Cadiz sur le benthos sublittoral du nord de la Bretagne. Helgolander Meeresunters. 33: 192-208 . Chasse, C. 1978. The ecological impact on and near shores by the Amoco Cadiz oil spill . Mar . Pollut . Bull . 9: 298-30 ~ .

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582 Vandermeulen , J. H., and D. C . Gordon , Jr . 1976 . Re-entry of f ire year old standard Bunker C fuel oil from a low-energy beach into the water, sediments, and biota of Cbedabucto Bay, Nova Scotia. J. Fish Res. Board Can. 33~9) :2002-2010. Woods , E. G ., and R. P . Hannah . 1981 . Txtoc I oil spill--The damage assessment program and ecological impact, pp. 439-443. In Proceedings, 1981 Oil Spill Conference. Publication 4334. Amer ican Petroleum Institute, Washington, D. C.