EVANS and RICE: EFFECTS OF OIL ON ECOSYSTEMS 



Crapp (1971b) observed that fucoid algae re- 

 placed barnacle and limpet populations near an 

 outfall where the effluent contained about 20-25 

 ppm oil from treated ballast water of tankers un- 

 loading at Milford Haven. Although the relative 

 oil content was low, the cumulative volume dis- 

 charged was large (20,000 gallons of oil per year), 

 a situation similar to that which may occur at Port 

 Valdez, Alaska, when the trans-Alaska pipeline is 

 completed. 



Blumer (1972) discussed how low-level chronic 

 effects of oil may damage marine organisms be- 

 cause of their dependence on natural organic 

 chemical clues for a variety of functions. Salmon 

 and other fishes utilize organic chemical clues in 

 migrations; predators are attracted to prey by or- 

 ganic compounds at the parts-per-billion level 

 (Whittle and Blumer, 1970); and other organisms 

 may use chemical clues for predator avoidance, 

 selection of habitat, and sex attraction. Blumer 



(1972) discussed the fears that oil pollution may 

 interfere with these fundamental biological pro- 

 cesses by masking or blocking, or by mimicking 

 natural stimuli (resulting in false responses). He 

 cited literature discussing the attraction of lob- 

 sters to kerosene and to purified hydrocarbon frac- 

 tions derived from kerosene and noted that many 

 dead lobsters were washed ashore after the West 

 Falmouth spill. Blumer's fears about interference 

 with chemoreception are further substantiated by 

 the observations of Takahashi and Kittredge 



(1973) on crab behavior. Crabs, Pachygrapsus 

 crassipes, exposed to water-soluble extracts of 

 crude oil failed to exhibit feeding behavior or mat- 

 ing behavior responses when given appropriate 

 chemical stimuli. Inhibition of chemoreception of 

 some motile marine bacteria by a crude oil and 

 several other hydrocarbons has been demon- 

 strated by Walsh and Mitchell (1973). 



Rice (1973) performed laboratory tests of avoid- 

 ance of pink salmon fry to Prudhoe Bay crude oil 

 and observed avoidance of oil at concentrations as 

 low as 1.6 mg/liter. He concluded that salmon fry 

 had the capability of detecting sublethal concen- 

 trations of oil and that they might avoid areas 

 contaminated with sublethal levels of oil, which 

 would result in confused and nonadaptive migra- 

 tory behavior. The effect of chronic low-level pollu- 

 tion in areas such as Port Valdez, the terminus of 

 the trans- Alaska oil pipeline, could be as severe as 

 the total loss of all salmon runs in the local area 

 because of altered behavioral responses to sub- 

 lethal oil pollution. 



CONCLUSIONS 



Although crude oil generally should be consid- 

 ered toxic to marine organisms and harmful to 

 their environment, most ecosystems can tolerate 

 some pollution because oil can be dissipated or 

 removed by processes like evaporation, autoxida- 

 tion, dilution, and biodegradation. However, each 

 organism and environment has a limit to how 

 much oil can be absorbed and metabolized. Cat- 

 astrophic spills are obviously pollution at a level 

 that ecosystems cannot tolerate without damage. 

 However, if the spills are not continued, the oil 

 will slowly be removed and recovery of the area, at 

 least to some degree, will likely occur. There is 

 some evidence for recovery of some affected indi- 

 viduals. 



Assessments of the impact of oil pollution can- 

 not depend solely on evaluation of immediate kills 

 of organisms from acute exposures. Chronic low- 

 level oil pollution can cause subtle changes in 

 organisms and is potentially more dangerous to 

 the ecosystem than dramatic catastrophic spills. 

 For this reason, the effects of chronic pollution 

 warrant intensive study so that they will not be 

 underestimated. The cumulative impact of 

 "ecological death" of individuals which have im- 

 paired functions may be quite significant, yet 

 difficult to assess because the death is not tied 

 directly to an acute oil exposure. Equally as 

 dangerous is the potential impact on populations 

 where reproductive processes, adversely affected 

 through physiological or behavioral mechanisms, 

 result in fewer progeny. Chronic pollution may 

 eliminate a species from an area entirely, and once 

 eliminated that species may remain suppressed 

 and may not repopulate the area because of con- 

 tinuing pollution or because its niche has been 

 filled by a more tolerant, possibly less desirable, 

 species. 



The adverse effects of oil on animal populations 

 has been of wide concern when stocks of special 

 interest, such as those providing the basis of a 

 sport or commercial fishery, have been involved. It 

 should be remembered that changes in popula- 

 tions of lesser apparent significance will also 

 cause changes in the community because each 

 species population interacts with and is dependent 

 on the rest of the community. 



The foregoing review of information does little 

 to simplify or ease the problems of policy makers 

 concerned with marine production and transpor- 

 tation of oil and petroleum products. The weight of 



635 



