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

Studies on settlement rate of Neodexiospira pseudocorrugata and Simplaria pseudomilitaris (Polychaeta, Spirorbidae) in the Port of Ischia. (Naples) are 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 unglazed 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 posed 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 pseudomilitaris did not reach brooding size within any of the monthly exposure periods. In and after August, an algal bloom of attached brown filaments (Ectocarpaceae) covered the tiles and was accompanied by decreased settlement and heavy mortality of spirorbids.