PATTERNS OF SHELL UTILIZATION IN 2 SYMPATRIC SPECIES OF HERMIT-CRABS FROM THE NATAL COAST (DECAPODA, ANOMURA, DIOGENIDAE)

Shell selection and utilization in two sympatric species of hermit crabs from the Natal coast, namely Clibanarius virescens (Krauss, 1843) and Calcinus laevimanus (Randall, 1840) were investigated. Shells of 23 gastropod species were occupied by C. virescens while 13 species were utilized by C. laevimanus. Shells of 11 gastropod species were inhabited by both crabs but, of these only two shell species were used in significant numbers. The results showed a close correlation between the morphometric data of the crabs and the utilized shells. Clibanarius virescens preferred high spired shells whilst C. laevimanus showed preference for shells with low spires. As C. laevimanus possesses a large cheliped it was restricted in the choice of shells in the natural habitat as it had to select shells with large apertures. Differential shell utilization has been advanced as the most important factor permitting coexistence of the two species. Clibanarius virescens inhabited a succession of shell species as the crabs grew in hard carapace or shield length whereas C. laevimanus showed preference mainly for two shell species namely Nerita albicilla Linnaeus, 1758 (carapace length less than 5 mm) and Turbo coronatus Gmelin, 1791 (carapace length more than 5 mm). Calcinus laevimanus may not be at a disadvantage by occupying Nerita shells as the large cheliped may be effectively used in sealing the aperture of the shell, and thereby minimizing water loss. Females of both species occupying lighter shells with large internal volumes were found to produce larger clutches as compared to females of similar carapace lengths occupying the heavier shell species.