Page images
PDF
EPUB

Numerous mortalities of benthic invertebrates have resulted from oil spills which have contacted the bottom community (Hampson and Sanders, 1969; Mulligan et al., 1974; Blumer et al., 1970; Sanders et al., 1979; 1980). The predominant cause of death is smothering. However, if the spill occurred recently (<3 days), little weathering would take place and the presence of the lighter, more toxic aromatic fraction may be a contributing factor. Sublethal concentrations of petroleum hydrocarbons result in cellular and physiological interferences and usually lead to forms of abnormal behavior such as disruption of feeding and/or reproductive patterns. At the present time, sublethal effects caused by petroleum hydrocarbons are not well documented. Due to the subjective nature of the analyses, and the relatively recent interest in the topic, there is little consensus among scientists as to the degree to which chronic doses of hydrocarbons will modify normal behavior or what effects may result, either long- or short-term. One factor which may confound our understanding of sublethal toxicity studies is the Arndt-Schult effect which is well known in toxicology (Laughlin et al., 1981). This effect results from the ability that some organisms have to compensate for minor toxic stress or in some cases, overcompensate which results in an enhanced physiological response to low level toxicant doses. This has been demonstrated by Laughlin et al. (1981) where crab zoeae had an increased growth rate when exposed to low concentrations of the water soluble fraction of jet fuel. The authors state that it is likely that many marine organisms have compensatory physiologies which would enable them to tolerate low concentration-low duration hydrocarbon inputs, but that long-term exposure is probably environmentally hazardous.

Ustach

Various other authors have conducted experiments to investigate physiological or etiological basis of organisms, responses to hydrocarbon pollutants. (1979) dosed the copepod Nitrocra affinis with the water soluble fraction of Louisiana crude oil in various concentrations. The author noted that brood size showed a statistically significant decline, but that the average life span and brood frequency were unchanged. Olla et al. (1983) reported that the clam Mercenaria mercenaria demonstrated a significant difference in the depth of burrowing after 96 hours in sediment contaminated with oil. The oil concentrations were 1-3 ppt and are comparable with those found after an oil spill. Behavior modification causing decreased burrow depth because of oil pollution has been reported also for other species of bivalve (Taylor & Karinen, 1977; Stekoll et al., 1980), Pearson et al. (1981) attributed an increase in predation on Protothica staminea (little neck clam) by Cancer magister to shallower burrow depth in oiled sediments. Sublethal doses of petroleum hydrocarbons which persist over time may also cause a decline in population size. Roesijadi and Anderson (1979) demonstrated that Macoma inquivata exposed to oiled sediments (inital concentration 1232.9 ppm) had decreased survivorship; reduced condition index (tissue dry weight/volume or length of shell); and lowered levels of certain amino acids (primarily glycine). Sublethal pollutant stress, such as indicated by this study, could result in reduced reproductive capacity in the affected population.

The direct impact to the benthos from oil spills will be greater in shallower water (<60 m) and in the intertidal zone, however the extent of the impact is dependent upon variables such as the total amount of area contacted, time of year, physical regime of the area, kind of crude oil product and type of biological system involved. The associated impact to the benthos could range from none to major depending upon the relative degree or status of those variables. The OSRAM predicts that, if a spill occurs, there is a 88 percent chance that it will decay at sea. This could cause an indirect major impact

to certain finfish or benthic invertebrate populations which utilize the planktonic/neustonic environments as nursery areas or modes of dispersion for larval stages. Many species demonstrate a contagious distribution of planktonic larval stages. Powles and Stender (1976) reported that one neuston net tow during an early spring cruise in the south Atlantic captured 44,350 larval spot (Leiostomus xanthurus), whereas the other 72 neuston tows during the cruise only captured an additional 164 specimens. The authors also stated that Brevoortia (menhaden) was the second most abundant genus, and the 7,472 specimens captured were taken in only 21 of the 73 neuston tows.

In summary the impacts which may be expected from an oil spill in the midAtlantic OCS region vary widely depending on independent, and indeterminant, factors such as location, size of spill, time of year, physical oceanographic and meteorologic conditions, and cleanup response. Major impacts may result in nearshore areas, or if the spill is coincident with planktonic larvae which demostrate contagious distribution. One spill greater than 1,000 bbl is assumed to result from the proposed action. This spill is expected to form a slick greater than 64,000 acres in area and has an estimated probability (as percent chance) of entering shallow water (<60 m) within 3 days of 15 percent and within 30 days of 41 percent. The percent probability of the oil spill reaching land (intertidal benthos) within 30 days is approximately 11 percent. Because of the high probability of risk of the spill entering shallow water, and the expected areal extent of the spill, an overall moderate impact to the benthos is expected. Localized major impacts to the benthos may occur depending on the concentration of oil transported to the sediments or if the spill reaches shore. Because the turnover rate of phytoplankton is relatively high, planktonic organisms are introduced into the sale area by water mass movement, the major planktonic species are widespread over the region, and the probability of a spill occurring at a critical time and place for meroplankton is low, impacts to plankton are expected to be minor.

[blocks in formation]

Information concerning bioaccumulation has been summa-
Both field and laboratory data

rized by Dames and Moore (1981).
have shown that marine animals can bioaccumulate heavy metals from drilling
fluids, thereby possibly introducing them into the food chain and creating
the potential for concentration in commercial resources and/or ingestion by
humans. Researchers using a variety of marine species such as shrimp
(Crangon sp., Pandulus sp.), sand worms (Nereis virens), mussels (Mytilus
edulis), and clams (Rangia cuneata) have demonstrated the uptake of various
metals, including Cr, Cd, Pb and Zn, by these organisms (Page et al. 1980;
McCullough et al., 1980). After depuration periods of 4-14 days, significant
quantities of Cr and Pb remained in the clam Rangia cuneata (McCullough et
al., 1980).

The sublethal effects of exposure to drilling fluids have been described predominantly for metal accumulation, although a few studies on growth, behavioral, histological and enzymatic changes have been reported. Exposure of amphipods (Onisimus sp., Boekosimus sp.), bivalves (Mytilus sp., Rangia sp., Crassostrea sp., Placopecten sp.), and shrimp (Palaemonetes sp.) to drilling fluids results in accumulation of a variety of metals, most notably barium (Ba), chromium (Cr), cadmium (Cd), lead (Pb), and zinc (Zn). The accumulations were relatively small and, with the exceptions of Ba and Zn, remained in the 1-10 ppm range (Petrazzulo, 1981). Uptake kinetics indicate

a plateau in metal accumulation frequently occurs between days 7 and 15; it is not clear that this plateau would continue over longer periods because these studies had a duration of only 7-30 days. Depuration appears to be effective at reducing metal accumulations releasing 50 to 100% percent of the excess accumulated metals (Petrazzulo, 1981).

The fraction that immediately dissolves from discharged drilling fluids may not be the only source of exposure for bioaccumulation. There are indications that a significant method of uptake may be through the solid fraction. Benthic organisms which feed on bottom sediments may become contaminated with heavy metals. Davis et al. (1981) determined that bioturbation is important in the release of heavy metals from contaminated sediments. They found that "burrowing and irrigation by infaunal polychaete worms significantly increase heavy metal release from sediment. The walls of burrows become exchange surfaces permitting release of metals into the burrow cavity. Irrigation by worms then flushes accumulated metal into the water column.'

Roesijadi et al. (1978) found that deposit and filter-feeding animals appeared to bioaccumulate much greater amounts of petroleum hydrocarbons from the surrounding water column than from oil contaminated sediments. During different depuration studies, crustacean zooplankton rapidly decreased stored hydrocarbons assimilated from the water to less than 5 percent of the starting value after 10 days (Corner et al., 1976; Lee 1975; Harris et al., 1977). For over a year after the West Falmouth spills, Burns and Teal (1971) found evidence of petroleum hydrocarbons in sediments, salt marsh plants, and marine organisms. However, there was no evidence of food chain magnification. Similarly, Mackie et al. (1975) could find no evidence of bio-magnification in their analyses of water, sediments, plankton, benthos, and fish from the Firth of Clyde in England.

Conclusion: The impact to plankton resulting from the proposed action is expected to be minor. Impacts to the benthos because of Sale No. 111 will be moderate.

f. Cumulative Impacts

Existing leases, transport of petroleum products through the present lease area and the proposed lease sale will have unavoidable impacts on the benthic environment resulting from oil spills and discharges of drill muds and cuttings. The discharges of drill muds and cuttings from existing leases are small in comparison to the proposed action and therefore are of minor importance to cumulative impacts. Impacts resulting from dredge spoil disposal in the nearshore environment are negligible and not important in the cumulative case. Trawling in shallow water could redistribute sediments. However, it is expected that the impacts which result would be negligible, and not distinguishable from natural resorting forces in the region. The impacts caused by drill muds and cuttings estimated to be discharged from operations resulting from the proposed lease sale will be highly variable, depending on location. The location of operations, because of the inherent mitigating variables of current velocity and water depth, will determine the degree of accumulation of drilling discharges. Because of the low toxicity and quick dilution of drill muds and cuttings, and the sediment resorting forces in the region, impacts are expected to persist less than one seasonal cycle and be localized and minor.

IV.E.3. Impacts on Marine and Coastal Birds

Marine and coastal birds could be exposed to several adverse or lethal impacts from OCS oil and gas exploration and development associated with proposed Sale No. 111. These impacts can be broken down into direct and indirect effects. Direct effects are caused by actual contact with a spill and they include matting of plumage which can reduce flying and swimming ability, loss of buoyancy which prevents resting and sleeping on the water, and loss of insulation resulting in death by exhaustion. thought that some species are actually attracted to oil slicks because the slicks appear as calm water areas or suggest concentrations of prey species. 011 ingestion and accumulation of toxic petroleum hydrocarbons can lead to reproductive failure and increased physiological stress which can reduce an animal's ability to survive. During the nesting season, oiled adults can transfer oil from their plumage to unhatched eggs or chicks, thereby reducing hatching and fledging success, respectively (Biderman and Drury, 1980).

Indirect effects are adverse impacts that can alter a species habitat, prey
availability, or cause a disruption of essential activities. The incorpora-
tion of crude oil into the sediments of a shallow bay, estuary, or wetland
could contaminate that habitat and depress populations of prey species
(primarily shellfish) for several years (Olsen, 1984). Construction activi-
ties, service vessel and helicopter traffic, and platform noises could
disturb nesting, migrating, feeding or resting birds.

Marine Birds

Among the marine birds, diving species and species that spend most of the time on the water's surface (e.g. murres, puffins, and cormorants) have a much greater risk of contacting oil. Because populations of these birds are very slow to replace lost numbers due to their low reproduction rates, oil spill mortalities could result in both short- and long-term adverse effects. Some investigators (Samuels and Ladino, 1984; Samuels and Lanfear, 1981; Wiens et al., 1979) have predicted, using population growth models for sea birds, that the loss of a significant number of breeding adults could result in a recovery time ranging from 5 to 10 years to over 100 years depending upon the severity of the spill and the resiliency of the population. One species in particular, the red phalarope, migrates through the Middle Atlantic Bight during April-May in large numbers. Because the continental slope is believed to be the central migratory corridor for the entire eastern North American population, this species would be especially vulnerable to oil spills in the vicinity of the slope during April-May. However, these birds are abundant during these two months only. In general, the mid-Atlantic supports low numbers of seabirds. It has been observed (Powers, Payne, and Fitch, 1982) that, in general, the Gulf of Maine and Georges Bank support greater numbers of seabirds than the mid-Atlantic region. In addition, the most likely number of oil spills estimated to result from the proposed action is only one (Table 1, Appendix C). Therefore, it is very unlikely that an oil spill from the proposed action will occur and severely impact seabirds inhabiting the mid-Atlantic region. The low level of support vessel traffic and activities associated with drilling operations are not expected to disrupt seabird behavior patterns (e.g. feeding and resting).

Small, chronic discharges of crude oil contained in formation waters may also pose an undetermined threat to the more pelagic species of marine birds.

The actual volume of crude oil that could be discharged would depend on several factors (e.g. volume of formation waters, petroleum content of formation waters). However, information obtained from the Gulf of Mexico (Final Regional Environmental Impact Statement, Appendix E, Minerals Management Service, 1982) indicates that on the average, 0.8 barrels of formation waters are produced for each barrel of crude oil recovered. The petroleum content of the formation waters averaged 25 ppm. Therefore, assuming these ratios and concentrations occur in the mid-Atlantic (an assumption that cannot yet be tested), approximately 4,000 barrels of crude oil contained in formation waters could be chronically discharged over the production life of the proposed sale. However, considering the size of the proposed lease area (approximately 20 million acres), the assumed oil production life of the field (approximately 30 years), and the estimated number of production platforms (4), the daily discharge rate should not pose a serious threat to pelagic species. some long-term adverse effects such as bioaccumulation of toxic petroleum by-products or increased mortality rates may occur.

Coastal Birds

Yet,

Shorebirds and wading birds are coastal waterbirds that would be vulnerable to both direct and indirect effects resulting from an oil spill that reached shore. Unlike marine birds, shorebirds and wading birds spend very little time on the water's surface and would be less likely to become severely oil fouled and die. However, they could ingest spilled oil or transfer it to their nests resulting in physiological disorders or loss of the nest. Indirect impacts such as habitat degradation or loss of prey would probably result in the most noticeable impact on these birds because of the limited amount of habitat available to them. Shorebirds have been found to avoid contaminated areas and to concentrate in oil-free areas following a spill (Chapman, 1984). If a spill should occur in the proposed sale area, there is a 22 percent or less probability that it would contact coastal waterbird areas within 30 days (Table 5, Appendix C) while a spill from a Sale No. 111 tanker bound for the Raritan or Delaware Bays would pose a higher risk of impact (28 percent) to these birds and their coastal habitats. Therefore, an oil spill resulting from the proposed sale could pose a moderate risk of impact to coastal waterbirds. Service vessel and helicopter traffic, and onshore support facilities are not expected to affect these birds as no significant filling of wetlands or coastal habitats will be required to accommodate OCS service vessels or support facilities. Waterfowl would be particularly vulnerable to oil spill impacts during their spring and fall migrations through the mid-Atlantic region. The most susceptible waterfowl are the sea ducks which migrate and winter off the coast. These birds have been found to suffer severe losses in numbers from large nearshore spills (Ohlendorf et al., 1978). The probability of an oil spill from the sale area contacting sea duck wintering areas or the major bays and sounds where they also congregate is 16 percent or less (see Table 5 of Appendix C). However, because sea ducks concentrate at the entrance to and within the Delaware Bay, the probability of a Sale No. 111 tanker spill affecting these birds increases to 24 percent. This indicates that the transporting of oil rather than the exploration and development of petroleum resources from this sale poses a greater threat to sea ducks. In addition, support vessel and helicopter traffic could disrupt normal waterfowl activities, but should not have a serious adverse effect.

« PreviousContinue »