It is likely that roughly one billion gallons of oil enters our oceans each year as a result of man's activities. Only 8% of this input is believed to derive from natural sources. At least 22% is intentionally released as a function of normal tanker “operational discharges,” 12% enters from accidental tanker spills and another 36% from runoff and municipal and industrial wastes.
Invertebrate populations and communities form the foundation for marine ecosystems and are continually subjected to stresses from both chronic and acute oil toxicity. The diversity of invertebrate taxa represented in the marine environment exhibit a wide range of responses to oil. Mortality is an obvious impact resulting from catastrophic spills or even chronic toxicity. Sublethal impacts on individuals are manifested by physiological, carcinogenic and cytogenetic effects. Impacts typically felt at the population level involve changes in abundance, age structure, population genetic structure, reproduction and reduced recruitment potential. Community level impacts are typified by modified interactions between competitors, predator/prey and symbionts. Most importantly, changes in community structure represented by altered trophic interactions tend to produce the most dramatic alterations to natural invertebrate assemblages.
Invertebrate communities respond to severe chronic oil pollution and/or acute catastrophic oil pollution in much the same way. Initial massive mortality and lowered community diversity is followed by extreme fluctuations in populationsof opportunistic mobile and sessile fauna (and flora). Oscillations in population numbers slowly dampen over time and diversity slowly increases to original levels. The time over which these events occur depends on the type of oil, the extent of the initial contamination, habitat type, weather conditions, latitude, the species assemblages represented and a myriad of other complex factors.