This chapter reports an extensive study of diatom communities developing on shells of marine gastropods, in the form of preliminary results from a still on-going research. We give emphasis upon the role of gastropod shells’ complexity in shaping and structuring diatom communities, and upon some strategies adopted by these algae to survive within these peculiar microenvironments. Our data show that diatom assemblages colonizing gastropod shells were mainly represented by pennate diatoms, with the adnate life forms, belonging to the biraphids (Amphora) and monoraphids (Cocconeis) taxonomic groups, contributing to the primary part of these epizoic communities. Amphora represented the dominant genus, because it was able to effectively colonize shell microenvironments, sometimes acquiring an endolithic life habitus that may be interpreted as a strategy to elude other competitors and grazers. Erect and motile diatoms occurred with lower abundance, because shell morphology might discourage their growth. Shell size influenced diatom communities, with the highest abundances being observed in bigger shells, whereas the shell morphology had an effect on the species composition, with the higher biodiversity being detected in shells with a more articulated structure. Our observations reveal that morphological differences in gastropods shells can act as a microselective constraint in the building process of epizoic diatom communities. In general ecological terms, the complexity of these substrates affects the structure of communities developing on them.
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