The Epibiotic and Endolithic Species Associated with the Gastropod Shells inhabited by the Hermit Crabs Paguristes Oculatus and Pagurus Cuanensis

Over 120 species, including epizoites, endolithic organisms, and an epiflora are associated with the gastropod shells inhabited by the hermit crabs Paguristes oculatus and Pagurus cuanensis in the North Adriatic Sea (Gulf of Trieste). The symbiotic organisms include members of three trophic levels - primary producers (rhodophytes), primary consumers (active and passive filter feeders), and secondary consumers (carnivorous species). Many of the invertebrates show a preferred distribution on the shells. The shells are a mobile substratum for a specific community. They are a sediment- and predator-free surface, and for their size are extremely stable substrates in terms of both time and orientation. The hermit crab microbiocoenosis is a dynamic phenomenon that can be studied as a functional unit. The symbionts are responsible for two simultaneous processes - a constructive and a destructive process on the shells. Shell deterioration is due primarily to biological processes, not to mechanical destruction. The more frequently occurring species were classified according to their role in reinforcing or weakening shell structure. These developments are related to hermit crab activity. Epizoites grow through several shell changes by hermit crabs, and a number of forms are capable of surviving the final deposition of the shells.