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However, within two years, they recovered to pre-spill levels. Productivity also showed similar trends. For example, the initial impact of the spill in the Bay of Morlaix, following the Amoco Cadiz spill in , was to kill off populations of the amphipod sand hopper, Ampelisca , which dominated the community [ 46 ]. Although the sediment was rapidly purged of the contaminating oil, it has been noted that Ampelisca was back to its pre-spill population density after 10 years.
Bioaccumulation in Marine Organisms
The standing crop biomass and productivity was restored much more rapidly as the ecological niches had been occupied by other opportunists like the bivalve Abra and the worm Nephtys. These had quickly filled the place left by the Ampelisca [ 46 ]. In other studies on oil spill accidents, it has been shown that six months after the Prestige oil spill and clean-up campaign, invertebrate populations of the exposed sandy beaches, notably the isopod Eurydice , the spionid polychaete Scoleleoius squamata , nemerteans and Diptera, were significantly reduced. Furthermore, their abundance inversely related with the oil pollution gradient.
The number of taxa was reduced but not the diversity values. The only clam on these sandy beaches was Donax. Before the spill and clean-up, it occurred in six beaches but afterwards, only in one. Upper dry sand communities were particularly reduced due to both oil toxicity and extensive beach grooming that also removed seaweed wrack [ 48 - 49 ]. Marine invertebrates are unique living organisms in different aspects. They have been explored as a model for several biological markers as a result of oil spill pollution. The results of a series of validation tests revealed that there were no significant reductions in the GST or CAT levels.
Six months immediately following the accident, observations indicated that the DNA adducts and MDA levels were high and the levels of AChE were significantly lower during the first year of the survey. This suggested a general stress.
Contributors and references
A simple multivariate graphic method - the integrated biomarker response index - was used to combine four of the five validated biomarkers and quantify the degree of impact on mussels at different sites. The results indicated that mussel populations were affected by the oil spill during only the first year after the accident.
In addition, recreational attractions for divers, coral reefs are considered to be important constituents of marine ecosystems. This is because they are important nurseries for shrimp, fish and other animals [ 51 ]. The aquatic organisms that live within and around the coral reefs are at risk of exposure to the toxic substances within oil, as well as smothering. They are rapidly deteriorating because of a variety of environmental and anthropogenic pressures. Thus, they are suffering significant changes in diversity, species abundance and habitat structure worldwide [ 52 ].
Oil dispersants are potentially harmful to marine life including coral reefs [ 53 ]. In a study using coral nubbins in coral reef ecotoxicology testing, [ 54 ] found that dispersed oil and oil dispersants are harmful to soft and hard coral species at early life stages. They found that the dispersant concentrations recommended by the manufacturer were highly toxic and resulted in mortality of all nubbins. The dispersed oil and the dispersants were significantly more toxic than the crude oil WSFs.
As corals are very sensitive to oil detergents and dispersed oil, the results of these assays indicated the negative and harmful effect of using any oil dispersant in coral reefs and in the area closely around them. These dispersants were rated based on their eco-toxicological impacts on the corals. Due to the well-developed hepatic mixed function oxygenase MFO system, in addition to the reactivity of the metabolites that would not be released in a toxic form during digestion and absorption, most fish, even in heavily oil-contaminated environments, do not accumulate and retain high concentrations of petroleum hydrocarbons.
Thus, they are not likely to transfer them to predators. Thus, no serious threat is predicted [55 as cited by 36]. Generally, marine carnivores are inefficient assimilators of petroleum compounds in food. For this reason, and because all prey species are able to release hydrocarbons from their tissues [41 as cited by 36], the marine food chain biomagnification does not occur. Thus, there is an indirect correlation between a marine mammal's trophic level and the concentration of residues that it might consume. In fact, as top carnivores that feed on large pelagic fish and seals, polar bears and killer whales are less likely to be exposed to petroleum in their food than other species, such as walrus and baleen whales, which feed on zooplankton and benthic invertebrates.
Experiments that explain the effect of oil spills on the early stages of fish were demonstrated by [ 56 ]. They found that chronic exposure of juvenile pink salmon Oncorhynchus gorbuscha to Alaska North slope crude oil resulted in a variety of responses. These included melanosis, erratic swimming, loss of equilibrium, reduced mobility and startled response.
Interestingly, the effects were not enhanced by the phototoxicity from UV irradiation, presumably of the highly pigmented nature of the fish's skin in contrast to phototoxicity in translucent early life stages of marine invertebrates. When they examined the phototoxicity of the water accommodated fractions of weathered crude oil, they found that pink salmon may be at less risk of photoenhanced toxicity, compared to the more translucent early-life stages of several other Alaskan species. As one of the major routes of exposure, physical contact usually affects birds.
For example, thousands of African penguins Spheniscus demerus were oiled following the Treasure oil spill in South Africa. An evaluation of the impact of oil spills on seabirds has not been fully appreciated during incidents, despite pressure from the public concern, media and other interested parties for precise and up-to-date information on the damage. Consequently, the approximate numbers of seabird casualties involved in many major spills have only been estimated, while impacts at the population level have been difficult to determine.
Natural variation and the huge range of factors that influence bird population statistics make it difficult to assess the impact of oil spill on sea birds.
In reference [ 57 ], in their efforts to assess the impact of oil spills on seabirds in Europe and in North America, the investigators reported that there are two inter-linked aspects to dealing with oiled seabirds during major spills. The first is a relatively expensive and logistically complicated process. This involves birds found alive and the humanitarian efforts made to clean, rehabilitate and successfully release them into the wild.
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The second involves assessing the likely impact of the spill on the populations of those species affected. The relation between the size of an oil spill and the number of seabird casualties is not directly proportional. Moreover, estimates of the number of seabird deaths from oil slicks are highly speculative. This is because an unknown number of oiled birds may die at sea and not reach the coast.
For example, following the Exxon Valdez oil spill, over 35, seabird carcasses were recovered in the northern Gulf of Alaska [ 58 ]. However, after the Braer accident [ 59 ], even though the Braer spill 85, tonnes was almost two and a half times as large as that of the Exxon Valdez Table 3 , only 1, dead birds were counted. Researchers argued that the rapid recovery of the murre breeding colonies in Alaska and the number of dead birds might be lower than was estimated.
They also suggested that breeding pairs may have been replaced by younger birds that came in from the open sea [ 60 ]. On the other hand, [ 61 ] argued that the impacts of the spill may have been diffused over a large area, permitting local recovery and making it difficult to detect any changes in local abundance or habitat occupancy. Nine years after the Exxon Valdez oil spill, in their long-term effects observation, [ 62 ] claimed that the populations of most bird species have not recovered and others still show potential population effects.
However, the report is at variance with other findings [ 63 - 64 ].
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During the winter season of , approximately 64, tonnes of Prestige heavy fuel oil spilled off Galacia, Spain. Reference [ 66 ] found that the kidneys of 32 oiled shag had extensive tissue damage and haemorrhaging. They further found that the oiled shag were heavily infected with an eimeriorin Apicomplex coccidian, which under normal circumstances is not pathogenic.
Biological Effects of Oil Releases - Oil in the Sea III - NCBI Bookshelf
Comparison of the number of dead seabirds recovered following the Exxon Valdez and Braer oil spills [ 47 ]. Marine mammals include bottlenose dolphins, fins, humpbacks, rights, sei whales, sperm whales, manatees, cetaceans, seals, sea otters and pinnipeds. As previously indicated, the physical contact of oil with furred mammals usually affects these animals because they rely on their outer coats for buoyancy and warmth. Consequently, these animals often succumb to hypothermia, drowning and smothering when oil flattens and adheres to the outer layer [ 24 ].
As part of their activities, all marine mammals spend a considerable amount of time at the surface. Here, they swim, breathe, feed or rest. Thus, the possibility of their contact with a surface slick, water-in-oil emulsion, or tar balls, is high. In heavy pelage marine mammals, such as fur seals, sea otters and polar bears, this contact may lead to fouling. Polar bears and otters groom themselves regularly as a means of maintaining the insulating properties of the fur and may, thereby, ingest oil.
Animals with smooth surfaces or relatively little to no pelage, such as whales, dolphins, manatees and most seals, have an advantage as oil would have fewer tendencies to adhere to their surface [ 36 ]. Some baleen whales are skim-feeders, i.