A study of the populations of Calliactis parasitica (Couch, 1842) in symbiosis with anomuran decapods in Thermaikos Gulf (N. Aegean Sea).

A wide range of meristic characteristics of the participants of the symbiotic relationship of Calliactis parasitica with decapod anomurans living in gastropod shells, from the North Aegean Sea (Thermaikos Gulf), was investigated. Using these data, attempts were made to determine the relative age (to size classes) of the anemones from this area, at their first association with an anomuran. It was found that anemones possessing a mean column diameter (mdC) of less than 0.5 cm, or a retracted column height (hC) of less than 0.4 cm, or anomurans possessing a cephalothorax length of less than 0.7 cm were not found living symbiotically in the study area. The anemone population also showed a shift in its distribution towards smaller and lighter individuals, indicating a possible preference for such anemones by the anomurans or the existence of an upper limit with regard to size for this particular symbiosis in the area and depths studied. We believe that both anemones and anomurans seek actively to initiate their symbiotic relationships from a relatively young age (in the first year of their life).The driving force behind this tendency for symbiosis should be attributed rather to biotic parameters which affect these organisms (predation and increased feeding possibilities) than to abiotic.