DO ASSOCIATED ZOOXANTHELLAE AND THE NATURE OF THE SUBSTRATUM AFFECT SURVIVAL, ATTACHMENT AND GROWTH OF CLIONA-VIRIDIS (PORIFERA, HADROMERIDA) - AN EXPERIMENTAL APPROACH

Massive specimens of Cliona viridis, collected off the coast of Blanes (North-Western Mediterranean Sea) in January 1987, were exposed to different light (natural day-night irradiance/constant darkness) and substrata (calcareous/siliceous) conditions to assess their influence on growth, survival and attachment rates. Sponges cultured under natural irradiance displayed higher growth rates with increasing temperature; those cultured in the dark did not respond to increased temperature, but adapted faster to laboratory conditions. Differences in growth rates between these two culture conditions are ascribed to the presence of a healthy symbiotical zooxanthellae population on individuals cultured under conditions of natural irradiance. Attachment rates of the cut sides of the sponges which were in direct contact with the substratum, also increased with increasing temperature, whilst sponge survival was not significantly dependent on temperature. The chemical nature of the substratum clearly affected survival rates, which were higher on calcified than on siliceous substrata.