Although there is little comprehensive documentation of long-term effects of acute or chronic oil pollution, possible long-term effects are diverse and complex, but may be roughly classified as () those related to the long-term recovery of a polluted ecosystem, () those due to chronic pollution (continuous or frequent inputs), and () those due to persistent contamination of ecosystems by petroleum hydrocarbons.

ECOSYSTEM RECOVERY

As there is disparate evidence on the acute effects of an oil spill, there are likewise varying estimates on the rates of recovery of disturbed ecosystems. At Santa Barbara, recolonization of affected rocky shores commenced within a month after dosage (). The intertidal biota now appears normal except in certain areas of heavy asphaltic deposits (). Likewise the rocky shore fauna affected by the oil spilled in the tanker collision at San Francisco seems to have recovered within a year or so (). On the other hand, benthic, intertidal, and marsh biotas remain affected at West Falmouth, even though the time for recovery has been about the same. Although the latter situation seems to be attributable to the persistence of oil in this environment rather than to a slow pace of biological succession, these examples do illustrate the variable nature of long-term recovery.

If the organisms of an area were severely depopulated but the oil did not persist within the system, recovery by the strictly biotic phenomenon of succession may be a slow process in the case of biologically highly "structured" communities. In natural communities one species may act to exclude or hold in check another through competition, predation, or grazing pressure. If the dominant species is removed or reduced below a certain level, the other species may then gain a foothold through atypical survival of the young and resist