Some ecological aspects of the land hermit crab Coenobita scaevola (Coenobitidae) at Wadi El-Gemal protected area, Red Sea

Abstract

Gastropod shells can be a limiting factor in allowing hermit crab populations to increase. The impact of this factor on population size of the land crab Coenobita scaevola (Forskäl, 1775) was examined. Extensive and intensive works were conducted on a sandy beach of Wadi El-Gemal island and the protected area coast (35°04'0"E, 24°42'0"N). Activity, spatial and temporal distribution, food foraging, and impact of human tourism activities for this hermit crab were discussed. A total of 365 crab individuals were collected from the sandy beach of Wadi El-Gemal island during August 2007 to July 2008, among these 137 were used for frequency measurements of occupied shells by the land hermit crabs. The hermit crabs were found occupying seventeen species of gastropod shells. A significant regression and correlation were recorded between the shell aperture and chelae. However, our data showing no significant regression values between total body weight of crabs and for each of the shell weight and internal volume. From the other angle, the correlation relationship recorded high significant value for the same relationships. This may reflect that some smaller crabs tend to occupy larger shells than the preferred ones. Moreover, the shell species occupation as a function of chelar hermit crabs size. While the negative results between body weight of crab and both shell internal volume and weight it may be due to the variations behavior of some land hermit crab individuals within population. It is logical that fit the size of chelae with aperture of shell to achieve protection from predators while some members of the population that occupied shell is greater than the size of his body to the unavailability of appropriate shells.