Population structure and dynamics of two scopimerine sand crabs Scopimera crabricauda Alcock 1900 and Dotilla sulcata (Forskåll 1775) in an estuarine habitat in Oman

Monthly samples of the scopimerine sand crabs, Scopimera crabricauda Alcock 1900 and Dotilla sulcata (Forskåll 1775), were collected from November 1992 to January 1994 from a marine inlet, Khawr Suwadi (23°45’N 57°47’E), in the Gulf of Oman. The crabs inhabited mobile sand banks and flats. S. crabricauda occurred at mean densities of 79 m⁻², between low high water neap and mean low water neap, and D. sulcata occurred at mean densities of 39 m⁻², below this and down to near mean low water spring. The largest individuals were males, but in general the adult crabs were small, ranging from 2.2–5.9 mm CW in S. crabricauda and 2.1–10.3 mm CW in D. sulcata. Juveniles of both species were present throughout the year, but seasonal recruitment varied between years and did not show a clear temporal relationship to the cycles of breeding as indicated by the percentage of ovigerous females in the population. In comparison with other members of the genera, female egg loads of both species were low. This can be accounted for by the small size of both species and additionally in D. sulcata the absence of any positive relationship between female size and clutch size.