MEPS 342:197-204 (2007)  -  doi:10.3354/meps342197

ABSTRACT: Estuarine fiddler crabs have a complex life cycle that spans vastly different salinity regimes. Larvae are spawned in estuaries and travel to the coastal ocean where development takes place; after metamorphosing to the megalopal stage, fiddler crabs reinvade estuaries where they settle and metamorphose. In the coastal ocean, larvae experience relatively stable physical conditions; however, upon reinvading estuaries, they are exposed to great fluxes in salinity and temperature. In this study, we measured shifts in the salinity regime caused by storm events, and determined the impact of these changes on species frequencies of megalopae from 3 Uca species in the water column and of their recently settled juvenile crabs on the benthos along a salt marsh creek in South Carolina. Adults of the 3 species examined are found in different salinity regimes: adult Uca pugnax generally occupy areas with relatively high salinity and plant cover, while U. minax are found in low salinity or freshwater areas; U. pugilator are found in open sandy areas over a broad range of salinities, but generally occupy higher salinity environments than U. minax. For megalopal stages in the water column, we found that the relative proportions of the 3 species changed significantly along salinity gradients and in response to storm events. When the salinity regime normalized, species frequencies for megalopae returned to pre-storm proportions. Only U. minax megalopae were present in the water column during a storm event in July, whereas U. pugnax had been the most abundant species in the water column prior to the storm. Although all 3 species were able to survive storm events as juveniles, U. pugnax juveniles survived low salinity conditions significantly better than the other 2 species during the July storm. During a less severe storm in August, which lasted 5 d and altered the existing profile for a week, the benthic juvenile stages did not exhibit significant changes in species frequencies. Our results show that the duration and severity of salinity change are important variables that impact on the presence of these Uca species in the water column, and suggest that the physiology and behavior of the megalopal stage strongly influence where populations occur within estuaries.

KEY WORDS: Salinity · Tolerance · Uca spp. · Estuarine crabs