Approximately 3.8 billion litres of oil enters the oceans yearly nearly all due to human activities (Suchanek 1993). Only 8% of this input is derived from natural sources such as seeps. By comparison, at least 22% is intentionally released through normal tanker “operational discharges” and 12% from accidental tanker spills. Other sources include inputs from municipal and industrial sources (c. 31%), atmospheric deposition (c. 9%), urban and river runoff (c. 5%), offshore oil production (c. 2%) and ocean dumping (c. 1%) (Suchanek 1993). Thus, although accidental spills of oil and petroleum compounds focus attention on the impacts of transient oil pollution events, a far greater annual volume is discharged into the sea through routine shipping operations. Oil and petroleum products impact on marine invertebrates by smothering (especially when the oil washes ashore and affects intertidal organisms) and toxicity, with both acute (lethal) and chronic (sub-lethal) effects. Some fractions are soluble and disperse throughout the water column, while heavier fractions may sink and cover benthic communities. Dispersants sprayed onto oil spills may simply facilitate the oil’s absorption into sediments and tissues and have been reported to be toxic to reef corals (e.g., Ballou et al. 1989). In addition, the immiscible surface fraction could affect light penetration and hence surface/upper pelagic communities of invertebrates and algae.

 

Studies of actual pollution events and manipulative experiments, on the effects of oil spills on intertidal communities were summarised by Suchanek (1993). Oil spills have been responsible for the destruction of entire coastal shallow-water communities that have taken years to recover (Peters et al. 1997). The effects of disasters such as the Exxon Valdez spill in Prince William Sound in Alaska (1988) have been well studied (e.g., Paine et al. 1996; Jewett et al. 1999). While the effects of such incidents (such as smothering of intertidal habitats) are obvious, chronic contamination by oil can also have an impact. For instance, sediments in areas of frequent shipping activity can be affected, as can interstitial species living in the littoral zone where large amounts of oil debris are common. Ponder (1990) described a mollusc community from upper littoral interstitial gravels at Ceuta in the Straits of Gibraltar, which survives only in a few small patches due to the large amount of oil and grease found in the interstitial spaces over most of the shore. Two species of interstitial slugs of the genus Smeagol (see Section 4.4.1) are known only from restricted areas in the upper littoral zone on the southern shore of Phillip Island (Tillier and Ponder 1992). This was the site of a recent serious oil spill which highlights the fact oil spills can result in the contraction of suitable habitat for certain species or potentially even cause extinction if the species has a restricted distribution within the affected area.

 

It is known that metamorphosis in some sea anenomes (Chieu and Berking 1997) and gamete production in some echinoderms (Nicol et al. 1977) are adversely affected by hydrocarbons.

 

A national plan has been formulated to combat pollution of the sea by oil and other noxious and hazardous substances[123] (AMSA 1997).



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Department of Environment and Heritage