Population dynamics and reproduction of Dissodactylus mellitae (Brachyura: Pinnotheridae) on its sand dollar host Mellita quinquiesperforata (Echinodermata)

Abstract

Population dynamics of the symbiotic crab Djssodactylus mellitae Rathbun were studied by monthly collections from their sand dollar host Mellita quinquiesperforata (Leske) in North Inlet, South Carolina, USA. Size frequency analysis of carapace widths indicated a 12 to 15 mo life cycle for D. mellitae. Larvae were released during summer, grew to produce one or more clutches of eggs the next summer, and died shortly thereafter. Sex ratio was 1:l throughout the year; females attained a slightly larger maximum size. Fecundity did not vary over the reproductive season (April through September) and mean egg number was 206 ? 62 (S. d.) eggs per clutch. Most recruitment occurred from May through September. D, mellitae differs from other species in the family Plnnotheridae in that males and females are more similar in size and longevity, there are no soft carapace stages, clutch size is relatively small and the entire clutch is completely covered by the abdomen. Accessibility of sand dollars to settling D. mellitae and protection provided to post-metamorphic individuals may decrease mortality enough to balance the small clutches produced by this crab.