Utilization of the intertidal zone of a salt marsh by the blue crab Callinectes sapidus density, return frequency, and feeding habits

The extent to which the blue crab Callinectes sapidus utilizes resources w i t h n the intertidal zone of salt marshes has not been quantified in a rigorous manner In the salt marshes of Sapelo Island, Georgia (USA), we sampled blue crabs using block nets as the crabs moved out of defined intertidal areas, determining the timing and extent of movement into, and feeding habits within, intertidal habitats.Blue crabs were absent or had a n extremely low density within an intertidal marsh impoundment during winter, when water temperature was below ca 15 "C.Juveniles 5 80 mm carapace width started moving into the Intertidal zone in March or April, but the intertidal density of blue crabs was dominated by larger juveniles and adults (> 80 mm) throughout the summers of the 2 5 yr study (March 1985 to August 1987).Densit~es were not large, peaking at 40 to 50 crabs ha-] {of total area sampled) during September.A non-impounded site located in a d~fferent local region had similar total densities to those of the impoundment, but had significantly more juveniles S 8 0 mm.Comparison of the size frequency distributions of blue crabs captured in the non-impounded intertidal area and in a nearby subtidal creek showed that all sizes of crabs ( 2 35 mm) moved into the intertidal zone of the marsh durlng the summer in approximate proportion to their abundance within the source (subtidal) population.On a shorter time scale during May-June, we captured more crabs in the impoundment during daytime vs nocturnal high tides.The extent of tidal inundation did not appear to greatly affect abundance here, although abundance during the lowest of the tidal heights was somewhat less than that during intermediate and high tidal heights.The principal prey consumed by relatively large (mostly > 100 mm) blue crabs within the study zone were natant fishes (38 '/o) and resident non-portunid crabs (43 %).Shrimp and similar crustaceans formed 12 % of the diet; other invertebrates such as gastropods and annelids a very small portion.Returns of individual blue crabs to the same intertidal marsh zone primarily occurred within 10 d of their initial capture, after which they apparently emigrated from the local area.This study provides the most complete synthesis available of the timing and extent to which blue crabs use the intertidal habitat of the salt marsh.