Do hermit crabs like living in sponges? Paguristes eremita and Suberites domuncula: biometric data from the southern Mediterranean Sea

A biometric analysis was performed on crabs (Paguristes eremita) collected in the soft bottom of the Sicilian Channel (southern Mediterranean Sea), on associated suberitid sponges (Suberites domuncula), and on shells inside sponges. Populations of crabs living in sponges overgrown on shells were compared with populations of crabs living in shells associated with the sea anemone Calliactis sp. Results from multivariate ordinations (principal component analysis, non-metric multidimensional scaling) and univariate linear regression analysis were discussed considering two possible models: (1) sponges are preferred to clean shell because they are a growing home; and (2) sponges are not preferred: they are used as an ‘emergency’ refuge by crabs searching for shells suitable for carrying sea anemones. Differences in shell assemblages and in biometric variables between populations living in sponges and populations living in shells associated with anemones, suggest that crabs, especially small ones, may live briefly in sponges and that sponges may be inhabited by a series of crabs over a long period.