Settlement patterns of two Spirorbidae (Annelida, Polychaeta) species in the harbour of Ischia (Gulf of Naples, Mediterranean Sea)

Studies on settlement rate of Neodexiospira pseudocorrugata and Simplaria p seudomilitaris (Polychaeta, Spirorbidae) in the Port of Ischia. (Naples) ar e reported. Observations were carried our monthly, during a one-year cycle (April 1995-April 1996) at two different depths (0.5 and 1.5 m) using ungla zed ceramic tiles as substrate. Both species reproduced throughout the year with maximum settlement in June and July at 1.5 m depth. On tiles err pose d during June, 40% of individuals of N. pseudocorrugata, ranging between 0. 8 and 1.6 mm coil diameter, were brooding, with broods smaller (6-14 eggs, egg diameter 75 mum) than in most spirorbid species. Simplaria pseudomilita ris did not reach brooding size within any of the monthly exposure periods. In and after August, an algal bloom of attached brown filaments (Ectocarpa ceae) covered the tiles and was accompanied by decreased settlement and hea vy mortality of spirorbids.