The Effect of Salinity on the Dispersal and Recruitment of Fiddler Crab Larvae

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Abstract
Behavioral and salinity tolerance studies of early and late stage larvae of U. pugnax were used to infer possible effects of salinity on the dispersal and recruitment of fiddler crabs. Larvae were induced to swim through salinity discontinuities of 0-10.permill. magnitude. Stage I zoeae were inhibited from moving upward through haloclines at .DELTA. salinity = 6, 8 and 10.permill., whereas stage V larvae tended to remain near the bottom of the water column and were inhibited from moving upward only at .DELTA. salinity = 10.permill.. Both stage I and V larvae passed downward through all haloclines. Larvae of U. pugnax were reared in 10, 20 and 30.permill. salinity water. Larvae were unsuccessful at molting in 10.permill. water. Zoeae reared at 20.permill. showed a slight delay in molting compared with larvae at 30.permill.. More stage V zoeae molted to megalopae at 30.permill. than at 20.permill., but more megalopae underwent metamorphosis to crab stage 1 at 20.permill. than at 30.permill.. These results support the hypothesis of transport of fiddler crab larvae from spawning areas to major estuaries and continental shelf regions. Only very sharp, steep haloclines would inhibit the vertical migrations of larvae. These results that larvae are retained nearshore in high salinity water during development and that metamorphosis is delayed until larvae reach lower salinity water characteristic of adult habitats.

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