On October 6, 1970, the small tanker Irini ran aground in the southern part of the Stockholm archipelago, releasing about 1000 t of medium and heavy fuel oil. Approximately 400 t drifted into a small bay, Gästviken, wiping out nearly the entire littoral fauna. Most of the oil was collected mechanically during the winter, and by May 1971 cleanup operations were completed. The recruitment of the bladder wrack (Fucus vesiculosus) community in the bay was observed at intervals over a 5-yr period. Significantly increased macrofauna population densities were found for a number of species in the 1974 and 1976 samples compared to those of 1971 and 1972. From June–July 1971 to June 1976, the mean numbers of individuals for all species rose from about 280 to 1000/100 g Fucus dry weight (d.w.). The bivalve Mytilus edulis increased in number from 0 to about 45, the gastropod Theodoxus fluviatilis from 0 to about 160, the amphipod Gammarus spp. from about 40 to 580, the isopods Idotea spp. from about 5 to 35, and Iaera spp. from almost 0 to about 10/100 g Fucus. Larvae of Chironomidae were the only group found with a decreased density between the first and sixth summers after the spill, with 240 and 145 individuals, respectively. The data obtained are discussed in relation to conditions in a nearby unpolluted bay and to normally occurring cyclic variations. Key words: algae, Fucus vesiculosus, littoral community, petroleum, pollution
AN OBSERVATION ON INTRACAPSULAR AND POST-EMBRYONIC PHASES OF RIVER NERITE (Theodoxus fluviatilis)