rations, or reproduction, as well as with the survival of aquatic organisms 

 in natural systems. Also, the mechanism through which behavior has become 

 altered in aquatic organisms exposed to pollutants is being examined. 



ECOSYSTEMS 



Field Studies 



One of the least explored areas of either ecology or environmental toxi- 

 cology is the ability of ecosystems to withstand contaminant stress. The 

 use of pesticides in environmental management and the deposition of indus- 

 trial contaminants in natural aquatic ecosystems has created a need for 

 studies on the effects of these materials on biological communities. Labo- 

 ratory studies can provide data on the effects of particular pesticides or 

 contaminants on many species of organisms under various environmental condi- 

 tions. However, such information may be of limited value at times in pre- 

 dicting the effects of pesticides and other contaminants on changes in 

 biological communities where many species interact. Contaminants may modify 

 these species interactions by affecting non-target organisms or be ecologi- 

 cally restructuring the biological community. These cause and effect ecolo- 

 gical interactions in natural aquatic communities can be estimated by mea- 

 suring certain characteristics such as primary productivity, standing crop, 

 species diversity, community respiration, nutrient cycling, etc. in con- 

 trolled lentic environments. Although chemical damage to a variety of eco- 

 systems is at least partially documented, and, in fact, has constituted a 

 major public and scientific concern in recent years, the facility with which 

 ecosystems may resist or recover from the action of toxic compounds has re- 

 ceived remarkably little attention. 



The presence of a contaminant in an ecosystem, however, does not in it- 

 self imply toxicity. The contaminant must first be biologically available 

 (Pavlou et al_. 1977). Toxicity is the characteristic of an individual or- 

 ganism's response to a chemical at a particular concentration or dosage for 

 a specific period of time. The effect of a contaminant on a community or 

 ecosystem will depend, therefore, upon the summation of all individual re- 

 sponses within affected populations. Even though toxicity is generally most 

 evident at the organismic and population level, community and ecosystem re- 

 sponses to organic contaminants can hypothetically be assessed directly or 

 indirectly. The indirect approach is more probably within the present know- 

 ledge base of ecology and toxicology and involves the determination and 

 monitoring of critical ecosystem processes. This approach is analogous to 

 the medical one where the disease or malfunction is ascertained by a set of 

 symptoms. Symptoms are functional evidences of disease, and the observance 

 and measurement of symptoms may be far removed f>"om the actual affected 

 organ(s) or system. 



Evaluation of the impact of contaminants on aquatic organisms has been 

 limited mainly to laboratory studies. Much of the laboratory research lacks 

 field verification and the true impact of contaminants on aquatic organisms 

 in the wild is poorly understood. The classical field approach involves 

 laborious age, growth, and population dynamics studies of fish and extensive 



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