would suggest that all have toxiceffects on one or more of the larval stages. In certain 

 experiments, such as those describing the effect of juvenile hormone mimics on lar- 

 vae of Rhithropanopeus harrisii, specific stages during larval development seem 

 more sensitive than others (Costlow, 1977). To test the degree to which individual 

 larval stages differ in levels of sensitivity to methoprene, larvae were treated in two 

 ways. In one series, larvae were maintained in three salinities combined with 0. 1 ppm 

 methoprene for specific periods of time and then removed to seawater without 

 methoprene for the remainder of their development. In another, they were initially 

 maintained in water without the methoprene and then moved to water containing 0. 1 

 ppm methoprene for the remainder of their larval and early juvenile lives. In both 

 instances, at the optimum salinitv of 20%o., relatively little mortality was observed 

 until day 13, which corresponded with the completion of the fourth zoeal molt to the 

 megalopal stage. None of the megalopa molting from zoea maintained under these 

 two conditions survived the final metamorphic molt to the first juvenile stage 

 (Costlow, 1977). As with studies on adult animals, however, levels of toxicity appear 

 to vary considerably, depending largely upon the species and the natural conditions 

 of salinity and temperature. 



Many sublethal effects have also been identified for adult and larval estuarine or- 

 ganisms, but the full implications of these studies are not totally understood. For ex- 

 ample, one juvenile hormone mimic, initially developed to inhibit the metamorpho- 

 sis of larval insects, has been shown to affect the reproductive cycle of one species of 

 intertidal crab (Payen and Costlow, 1977). 



Studies on the effects of methoxychlor on several species of crustacean larvae 

 demonstrate several sublethal effects. Although exposures of up to 10 ;ug/ 1 of 

 methoxychlor did not reduce the percentage of Cancer magister eggs hatching within 

 24 hours, successful development to the extremely short prezoea stage decreased 

 over that observed in the controls (Armstrong et al., 1976). Only 70 percent of 

 hatched organisms successfully molted to the first true zoea. A reduction in motility 

 was observed in 50 to 90 percent of those that did develop when they were reared in 

 concentrations of methoxychlor ranging from 0.18 to 1.0 /ug/1. 



Concentrations of Dimilin® ranging from I to 10 ppb did not affect the survival of 

 adult copzpods ( Acartia tonsa)b\i\ did alter the viability of eggs produced by females 

 maintained in this insect growth regulator (Tester and Costlow, 1979). When females 

 were maintained in 10 ppb Dimilin® for periods rangingfrom 12 to 36 hours, the per- 

 centage of eggs hatching decreased from 93.4 to 1.2. Concentrations of 1 ppb 

 Dimilin® also reduced egg viability, an effect that was most pronounced following 

 36 to 60 hours of treatment. Those eggs that did not hatch were fully developed and 

 appeared to be viable, with nauplii observed moving within the egg membranes. The 

 nauplii that did hatch later in the treatment period were of abnormal shape and failed 

 to molt to the second naupliar stage. Most frequently, body and appendage shape 

 and setae were found to be abnormal (Tester and Costlow, 1979). 



Juveniles of Cancer magister exposed to methoxychlor were found to be smaller 

 than crabs within the control series. Sensitivity of juvenile crabs to this compound 

 appear to be greatest during the period of ecdysis or shortly thereafter. Adult crabs 

 exposed to methoxychlor were hyperactive, exhibiting much more frequent move- 

 ment of mouthparts and chelipeds than observed in the control animals. The more 

 severely affected crabs were incapable of maintaining an upright posture, and some 

 remained supine for several weeks before death. Crabs exposed to 40 /xg/ 1 of methoxy- 

 chlor ceased to eat, whereas crabs exposed to considerably lower levels appeared to 

 have difficulty in locating food. They were also observed to tear at the food, leaving it 

 scattered within the container rather than ingesting it. 



Similar behavioral changes associated with the ingestion of small amounts of pes- 

 ticide have been recorded. After exposure to DDT, fiddler crabs exhibited a variety 

 of behavioral irregularities (Odum et al., 1969), and Klein and Lincer (1974) ob- 

 served similar behavioral changes after Uca pugilator had ingested small amounts of 

 dieldrin. After exposure to 10 ppm dieldrin, the adult crabs were unable to right 



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