EFFECTS OF PESTICIDES ON EMBRYONIC DEVELOPMENT OF CLAMS 

 AND OYSTERS AND ON SURVIVAL AND GROWTH OF THE LARVAE 



BY HARRY C. DAVIS AND HERBERT HIDU ', Fishery Biologists 



BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY 



MILFORD, CONNECTICUT 06460 



ABSTRACT 



Fifty-two coinpoiiniis were tested for their effects on 

 embryos of the haril clam, Mercenaria mercenaria, and 

 the American oyster, Crassostrea virginica, and on their 

 larvae. The pesticides included 17 insecticides, 12 her- 

 bicides, one nematocide, four solvents, and 18 miscel- 

 laneous bactericides, fungicides, and algicides. 



Most of the compounds affected einbryonic develop- 

 ment more than survival or growth of larvae. Soine, 

 however, drastically reduced growth of larvae at con- 



centrations that had relatively little effect on embry- 

 onic development. It is necessary, therefore, to evaluate 

 the effects of pesticides on all stages of the life cycle of 

 an organism before the pesticide can be considered safe. 

 Nevertheless, differences in toxicity to bivalve larvae 

 among compounds of each category of pesticide are 

 large enough that it should be possible to select com- 

 pounds to control pest species without serious damage 

 to commercial shellfish. 



The extensive use in recent years of highly 

 persistent jjesticides for control of certain insects 

 and luidesirable plants, not only on agricultural 

 lands but also on recreational areas, lakes, streams, 

 and marshes, has made imperative an evaluation 

 of tlie effects of these compounds on fish and 

 wildlife. The eventual goal is to control undesiral)le 

 species, witli the least harm to the desiraljle 

 members of the ecosystem. Attainment of tiiis goal 

 recj'iires extensi\'e knowledge of how eacli iiesticide 

 affects each species or representative s])ecies of 

 the system. Also, the pesticide must be liighly 

 specific or be applied so that its dispersion is 

 strictly limited. 



Pesticides may enter tlie lialiitat of shellfish in 

 several ways. One is by being carried there in 

 runoff water from treated land areas, (.'ottam 

 (1960) stated that 2 to 3 billion pounds (9.07 to 

 13. Gl X 10- kg.) of [pesticides are used annually' in 

 the United .States on about 100 million acres 

 (40.5 X Kf ha.) of laud. Thimann (1964) stated 

 that the United States used 175,000 short tons 

 (158,760 metric tons) of insecticides in 1962 and 

 about half tliat much of fungicides and herl)icides. 



DoudorofT, Katz, and Tarzwell (1953) made 

 laboratory tests of soUs collected from toxaphene- 

 treated fields and conchuh'd tliat stream waters 

 can be made toxic to fish by the drainage from 

 such fields. .Such runoff water may carry the 

 ])esticides in solution, adsorbed on suspended 

 particles, or incori)orated in plants and animals 

 in the water. Certainly, large quantities of the 

 pesticides that leach from the soil must eventually 

 reach coastal marine waters and sediments. 



A second, more direct, and periiaps more 

 easil_v regulated method by which [>esticides may 

 enter the estuarine enxironment is the use of 

 insecticides anil herbicides on salt marshes and 

 estuaries to control mosqiuloes and undesiral^le 

 l)lants. In some regions large areas are sprayed 

 near shellfish beds. Pesticides used in tins way 

 probal)ly create higlier concentrations of the 

 active ingredients in the estuarine water tlum are 

 achieved by any other metiiod. 



Loosanoff, MacKenzie, and Shearer (1959 -), 

 Loosanoff et al. (1960), and Loosanoft' (1961) 

 ])roposed the use of several jiesticides for the 

 control of certain predators and competitors of 



1 Present addiessi University of Maryland. Natural Resources Institute, 

 Box 3S, Solomons, lid. 20088. 

 Published -\ljril Iii69. 



2 Lousanoll. V. L., C. L. MacKenzie, .Ir.. and L. W. Shearer. lOS'.i. I'se 

 of chemical tiarriers to protect shellfish lieils from predators. Bur. Comnier. 

 Fish. Biol. Lab., MiUord, Conn., Bull. O, L'ii: 1-11. 



FISHERY lULLETIX: \X)L. 67, NO. 



39.3 



