Seasonal variation, shell selection, and morphometric relationships of the hermit crab Clibanarius erythropus on the rocky shores of Tolmeitha, eastern Libya

Abstract

This study investigated four main aspects of the hermit crab Clibanarius erythropus along the rocky shores of Tolmeitha, eastern Libya. Monthly sampling was conducted from June 2023 to May 2024 using quadrats on subtidal rocky bottoms. A total of 46 crabs were collected across all sampling events. The first objective examined seasonal variation in density, body weight, and carapace length. Density varied significantly among seasons, with the highest values in summer and the lowest in winter. Body weight peaked in spring, while carapace length showed no significant seasonal change. The second objective identified the gastropod shell species occupied by this crab. Nine gastropod shell species were recorded, with Phorcus articulatus being the most frequently occupied shell, particularly in summer. The third objective described the demographic structure. Adults dominated the population, and the sex ratio did not differ from equality, with ovigerous females present across seasons. The fourth objective quantified morphometric relationships between crab size and shell dimensions. Positive correlations were observed between crab length and shell length, crab weight and shell weight, and shield length with both shell length and shell width. The relationship with shell width was stronger than that with shell length. These results fill a specific knowledge gap for the Tolmeitha coast, as no previous study has documented shell selection patterns or population structure of C. erythropus in this part of eastern Libya. This baseline provides a reference for future monitoring of intertidal communities in the southern Mediterranean, particularly in understudied coastal areas of North Africa.