After reading this article you will learn about the effects of oil pollution on marine biota.
Effect of Oil Pollution on Phytoplankton:
The general impression emerging from various studies is that although natural phytoplankton communities are adversely affected by oil, these organisms are sufficiently prolific that individual spills have only short-term effects on their overall populations.
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However, since phytoplankton is largely responsible for the fixation of the energy utilised by marine ecosystems, it is vital to know how oil in the water column affects it both as large spills and as continuous additions in estuarine, coastal and oceanic environments.
Unfortunately, it is very difficult to detect the effects of oil on species abundance and composition of phytoplankton in the field, as these organisms show drastic natural seasonal variations with one species of diatom or dino-flagellate taking over the predominant position held by another species as consequence of changes in temperature, light or the availability of nutrients.
However, there are several sensitive phytoplanktonic species. These species showed retarded cell division or death of cell even at very low oil concentration (0.1 to 0.00001 ml/lit). The species of Coscinodiscus, Skeletonema, Chlorella and Chlamydomonas showed marked sensitivity to oil pollution in marine environment.
Effect of Oil Pollution on Zooplanktons:
Cope pods are most sensitive zooplanktons, young Acartia clousi and Oithona sora die after 3-4 days immersion in sea water containing 10 µg/lit. of oil, while the adults of these and three other cope pod species suffer an accelerated death after longer exposures to 10 µg/lit. or after 5-60 minutes in 1,000 µg/lit.
Effect of Oil Pollution on Macroscopic Algae:
The growth and survibility of sea weeds like Macrocystis, Fucus, Ascophyllum, Sargassum are seriously affected by oil spill as reported after TORREY CANYON spill or TAMPICO MARU spill. The destruction of spore-lings of Polysiphonia species, inhibition of gross photosynthetic activities of some green algae like Enteromorpha and Chaetomorpha are marked affected by oil pollution.
However, some algal forms, particularly the blue-green algae, appear to be resistant to oil pollution and may even obtain nutrients from it. For instance Oscillatoria—a typical blue-green algae — grows abundantly on trickling filters used to remove oil from refinery effluents.
Effect of Oil Pollution on Marine Grasses:
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Much of the information regarding the effects of oil pollution on marine grasses and marsh plants has been gathered by workers at the Orielton Field station in Pembroke, Wales, where extensive studies have been made on the effects of oil on salt marsh plants.
It was reported that Spartina Sp., Sueda maritina, Salicornia Sp. are very sensitive to oil pollution, while Oenanthe lachesali, a tolerant perennial marsh plants. Further it was also reported that the growth of some marsh grasses (Pucinella maritinia and Festuca rubra) may be stimulated by oil pollution.
Effect of Oil Pollution on Benthic and Intertidal Organisms:
By far the greatest number of information concerning the effects of petroleum pollution on marine organisms pertains to benthic and intertidal organisms; that is, those organisms which spend a major portion of their lives at the sea bottom. These organisms include a large number of species of molluscs, crustaceans, echinoderms, polychaetes, coelenterates and hydroids.
Many of these, notably lobsters, oysters, scallops and clams, not only constitute an important fisheries resources but are also amenable to Mari culture. These creatures are very susceptible to oil pollution because many of them inhabit the intertidal zone where they become coated with oil and smothered in the event that heavy oil drifts onto the shore.
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Many of them are filter-feeders which indiscriminately extract fine particles of a certain size range from the water and thereby ingest oil present as droplets or adsorbed on the other particulate material.
In a large spill in the coastal area, molluscs frequently suffer heavy mortalities. Subsequent re-colonisation needs several years together. It is, however, interesting to note that oysters, black sea mussel could withstand oil pollution up to a certain extent, as they could intake petroleum hydrocarbons from the environment into their lipid pool.
Crude oils, oil derivatives and oil-dispersant emulsions are harmful to the larvae of some marine bivalve molluscs as shown by experiments. But common blue mussel (Mytilus edulis) was very much tolerant to oil pollution and these forms can readily take up the hydrocarbons.
The mobile crustaceans, lobsters, crabs etc., however, suffer heavy mortalities due to oil pollution. A wide variety of benthic invertebrates was killed by diesel oil spill into Puget Sound in 1971; with mortalities for 48 species of intertidal invertebrates ranging from 30-100%, the hardest bit belong to brittle stars, polychaetes, semertans, chitors, hermit crabs and limpets.
Effect of Oil Pollution on Fish and Fisheries:
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It is probable that fish swim away from heavy oil pollution and particularly from oil spills, where the oil spilled on the ocean causes a decrease in photosynthesis and, consequently, a lowering of oxygen levels in the water.
The slimy mucus on the gills of fish make them somewhat resistant to oil. However, there is much evidence that fish are adversely affected by both spilled petroleum and chronic pollution by refined petroleum products.
There were significant fish fall (at least 10%) following the oil spill from the Ocean Eagle in the harbour at Puerto Rico; spilled heavy fuel oil at Wave Island and West Falmonth, Massachusetts, also resulted in the death of many fishes. Fisheries are adversely affected by chronic petroleum pollution, and the catch of fish off the coast of Louisiana has decreased concomitantly with the development of the petroleum industries.
The greatest harm to fish life from petroleum hydrocarbons from both spillage and chronic pollution is the effect on eggs, larval stages, and fry. The destruction of young fish can have serious long-term consequences. After the Torrey Canyon accident (1967), 50 – 90% of the eggs of pilchards in Cornish waters were dead.
Effect of Oil Pollution on Birds and Mammals:
The oiling of birds in the marine environment has received considerable publicity and is a serious problem associated with oil spills and oil slicks emanating from wasting of tankers.
These oiling can be catastrophic for a population as migratory activity can bring a major proportion of a bird species to a confined area, oil fouling of birds can cause a disruption in the insulating capacity of feathers and result in death from pneumonia or it can cause a loss in buoyance and subsequent drowning.
The estimated number of birds that died as a result of typical spills are as follows: Torrey Canyon 40,000- 100,000; Santa Barbara blowout 3,600; San Francisco Bay spill 7,000; standing of the Gerd Maersk in the Elbe Estuary, 250,000-500,000. The birds, like walruses, sea lions and seals are potential victims of oil pollution.
The mortality of sea birds resulting from oil spills is given in Table 12.3:
Effect of Oil Pollution on Coral Reefs:
Coral reefs generally formed in tropical oceans are an environment of enormous biological diversity, complexity and productivity. The branched corals are particularly sensitive to oil and markedly so while exposed to air and many reefs in the Pacific Ocean and Indian Ocean protrude far above the water surface at low tide.
It would be harmful to the reef if significant quantities of toxic petroleum were absorbed into this integral part of the bio-system.
Thus the overall effects of petroleum hydrocarbons in the marine environment may be summarised as follows:
(i) The introduction of high concentration of selected hydrocarbon factors can be lethal to seafood species. At sub-lethal levels, the seafood can contain hazardous concentrations of petroleum hydrocarbons or be tainted such that taste or aroma renders the food unfit for human consumption. This is of considerable consequence to the commercial seafood industry.
(ii) Oil slicks on water or oil deposited on beaches are unsightly and tar lumps carried by the tides onto beaches adjacent to major shipping lines (Florida Coast, Bermuda) are undesirable from an aesthetic standpoint.
(iii) A decrease in diversity and/or productivity of a species can bring about modifications that can have long-range deleterious effects on the entire marine ecosystem.
(iv) Extensive damage to wild life, generally caused by large spills or blowouts in offshore drilling, can significantly decrease population of seabirds and marine mammals.
A summarised view of oil spill effect on oceanic communities is given in Table 12.4:
