or mimic the action of insect hormones in such a way as to prevent growth or 

 metamorphosis. 



There appears to be a reduction in the number of compounds that are broadly 

 toxic to biological systems and an increase in the number of compounds developed 

 specifically to inhibit enzymatic or hormonal reactions in insects. This development 

 frequently proceeded without consideration of the extent to which these same 

 enzyme and hormonal systems are found in arthropods in general, including virtu- 

 ally all of the marine Crustacea, and what effect these compounds might therefore 

 have on those nontarget arthropods closely related to the insects. In addition to those 

 marine Crustacea that are commercially important — the penaeid shrimps and a 

 number of species of crabs, for example — the commercial finfisheries of the United 

 States depend on a variety and abundance of marine Crustacea found within the 

 planktonic food web. Nothing is known about the effects of the more specific com- 

 pounds available at the beginning of the eighties on food web Crustacea. The extent 

 to which many of these compounds may be accumulated through the food chain has 

 been identified for a relatively small number of compounds. 



GENERAL EFFECTS OF TOXIC ORGANICS ON ESTUARINE 

 BIOLOGICAL SYSTEMS 



A considerable number of scientific publications, agency reports, and periodic 

 reviews on effects of toxic organics have appeared during the seventies (Walsh, 

 1972). In fact, the emergence of literature dealing with environmental pollution from 

 heavy metals, organics, and petrochemical compounds has led to the development of 

 specific scientific journals devoted to these topics. Papers have dealt with sublethal 

 and lethal effects of specific compounds on individual species; behavioral and physi- 

 ological responses to specific compounds; bioaccumulation and residual amounts of 

 organic compounds in estuarine animals, plants, and sediments; and a consideration 

 of adequate methods to analyze and evaluate the impact of toxic materials in estu- 

 arine and marine waters. 



Pesticides 



Although the lethal effects on marine fish, crabs, and molluscs of many organic 

 compounds used as pesticides are generally well documented, the number of com- 

 pounds that have been examined in detail for their toxic effects on each of these 

 groups is extremely small. In studies involving post-larvae of differing species, there 

 appears to be considerable variation in the levels of toxicity of many of the com- 

 pounds. This is in part due to the physiological state or stage of development of the 

 organisms under study. For example, juvenile Cancer magister exposed to 4.0 mg/ 1 

 of methoxychlor died within 72 hours after application, whereas adult crabs of the 

 same species died only when exposed to 40.0 mg 1 ( Armstrong et al., 1 976). This level 

 of toxicity in Dungeness crabs is similar to that described for DDT ( Poole and Willis, 

 1970), and the decline in landings of this species in San Francisco has been attributed 

 to the increased use of pesticides in that area. Williams and Duke( 1979) summarized 

 much of the available literature on the effects of many chlorinated hydrocarbons, 

 organophosphates, carbamates, juvenile hormone mimics, and insect growth regula- 

 tors on estuarine Crustacea. They concluded that such compounds as dieldrin, DDT 

 and its metabolites, Kepone, mirex, malathion, and carbofuran almost always have 

 toxic effects on adult blue crabs, fiddler crabs, and estuarine shrimps. 



Lethal levels for many planktonic organisms, including the larvae of marine Crus- 

 tacea, have also been documented. Epifanio (1979) considered the work of several 

 recently published authors in arriving at an understanding of how chlorinated 

 hydrocarbons, organophosphates, carbamates, and juvenile hormone mimics affect 

 the survival of larvae of many estuarine crabs. The relatively limited number of 

 observations, most of which deal with the effects of chlorinated hydrocarbons. 



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