FISHERY BULLETIN: VOL. 72, NO. 3 



a tropical system. Odum (1970) noted, however, 

 that many estuarine species are living near the 

 limit of their tolerance range and that any altera- 

 tion in the environment, such as additional stress- 

 es caused by low levels of pollution, could exclude 

 these animals permanently from the estuary. 



All healthy balanced ecosystems are generally 

 functioning at or near some critical tolerance 

 limit. In an ecosystem with a variable environ- 

 ment, such as a north temperate estuary, re- 

 sponses to additional stress might not always be 

 the same. For example, even though factors sur- 

 rounding an oil pollution incident might be out- 

 wardly similar in most respects to another spill in 

 a comparable area, the biological impacts may 

 differ. The ability of the local community to absorb 

 the additional stress will be influenced by the 

 coincidence of seasonal variability of natural 

 stresses, the differences in vulnerability of stages 

 in an organism's life cycle, and many other 

 dynamic features of the ecosystem. 



Biological Differences 



The effects of oil pollution on many different 

 organisms in various habitats may vary from no 

 effect to responses of avoidance and decreased ac- 

 tivity, to nonadaptive responses of panic and 

 physiological stress. What kills one species may 

 have little or no effect on another. Affected or- 

 ganisms vary from single cells, to sedentary 

 clams, to highly mobile predators, each of which 

 has different behavioral and physiological in- 

 teractions with the environment. 



Just as different species are affected differently, 

 so may individuals within a species be affected 

 differently. In particular, different life stages such 

 as eggs, hatched larvae, and newly molted indi- 

 viduals may have different sensitivity to the same 

 level of pollution. Mironov (1968), for example, 

 reported that prelarval stages of barnacle, 

 Balanus sp., were 100 times more sensitive to oil 

 pollution than the adult form. This contrasts with 

 the relative lack of sensitivity to crude oil by pink 

 salmon eggs and sac fry, which were 10 times 

 more tolerant than older fry (Stanley D. Rice and 

 Adam Moles, Auke Bay Fisheries Laboratory, Na- 

 tional Marine Fisheries Service (NMFS), NOAA, 

 Auke Bay, AK 99821, pers. commun.). 



Renzoni (1973) conducted a series of experi- 

 ments on the toxicity of several crude oils and 

 petroleum products to the sperm, eggs, and larvae 

 of the oysters Crassostrea angulata and C. gigas 

 and the mussel Mytilus galloprovincialis. He 



found a relatively high degree of tolerance by eggs 

 and larvae but reported that the fertilizing capac- 

 ity of sperm was markedly affected by similar 

 exposures. 



Biodegradation 



Quantitative data describing the biodegrada- 

 tion of various components of crude oil, especially 

 in arctic and subarctic areas, are limited. 



ZoBell ( 1973a) briefly reviewed the current un- 

 derstanding of microbial degradation of oil, in- 

 cluding interactions, limiting factors, problems, 

 and perspectives. Ahearn (1973) stated that re- 

 search on microbial utilization of hydrocarbons 

 for treatment of oily pollutants in the environ- 

 ment, though more intensive in recent times, is 

 still in an early stage of development. It is known 

 that microorganisms can degrade much of a 

 crude oil, particularly the less toxic paraffinic 

 compounds. No single species can degrade all the 

 compounds, but many different species together 

 can metabolize a large number of the compounds, 

 if not all. The rate of microbial degradation, 

 which is principally aerobic, decreases with a 

 decrease in temperature. Large quantities of 

 oxygen are needed. It has been estimated, for 

 instance, that complete oxidation of 1 gallon of 

 crude oil would require all of the dissolved 

 oxygen in 320,000 gallons of water. This com- 

 parison may be unrealistic because most oil is at 

 the surface of water in contact with air and only 

 the outer surfaces of oil can be attacked at any 

 one time. It is reasonable to assume, however, 

 that an oxygen-deficient environment may well 

 occur under some oil slicks and in oil-contam- 

 inated sediments. 



Glaeser and Vance (1971) studied the behavior 

 of Prudhoe Bay crude oil in controlled spills in the 

 Chukchi Sea but were not able to isolate any mi- 

 croorganisms which could degrade hydrocarbons 

 at the ambient temperatures of the Arctic, al- 

 though some emulsification of the crude oil was 

 observed. However, ZoBell and Agosti (1972) col- 

 lected oil-oxidizing bacteria near natural oil seeps 

 from the Alaska North Slope and observed oxida- 

 tion rates of mineral oil at -1°C and above. They 

 noted that the solid surfaces of the ice crystals 

 appeared to facilitate bacterial growth, because 

 the rate at -1°C was substantial and near the 

 4°C rate. 



The apparent contradiction between the studies 

 is probably best explained by ZoBell's (1973b) con- 

 tinued observations with North Slope bacteria. He 



628 



