Preliminary information on bryozoans associated with selected infralittoral algae communities from eastern Sicily (Mediterranean)

Bryozoans have been studied from six samples collected in degraded Cystoseira brachycarpa, C. sauvageauana andC. spinosa communities (Infralittoral Algae Biocoenosis — IA), developed at 5, 10 and 25 m depth, respectively, along eastern Sicily, Mediterranean Sea. Bryozoan communities consist of 59 species including 14 cyclostomes, three ctenostomes and 42 cheilostomes. The total species richness is relatively low in relation to that of the IA Biocoenosis and of other habitats in the Mediterranean. The proportion of cyclostomes is high at species level and colony abundance, mostly in separate samples. Several species occur only at one site, associated with volcanic ash and shells. Only a few algal species are colonised, and bryozoans seem to select particular species and parts of algae in relation to their rigidity and the possible increase of shadowing in dense canopies. Erect-flexible colonies, unserial runners and small unilaminar growth morphologies are selected, as well as poorly or non-mineralised skeletons. Species richness and colony abundance varied between sites for each community and generally increased with depth, possibly in relation to decreasing disturbance (waves, light penetration, temperature variability) and local environmental changes (sediment smothering) and consequent replacement of algal species. Comparison with previous data indicates a reduction of species richness through time that cannot be unequivocally interpreted with the present data, but which is possibly related to the general deterioration of Cystoseira communities in the area and in the Mediterranean as a whole.