Studies on the meroplankton in the inner Oslofjord I. Composition of the plankton at Nakkholmen during a whole year

Abstract

Abstract The meroplankton at Nakkholmen in the inner Oslofjord has been studied during one annual cycle (December 1963–December 1964). Each of the 70 samples taken consisted of the larvae from 1000 litres of sea water delivered by a suction pump and filtered through a 125 μ plankton net. In total, these samples contained about 182,000 larvae belonging to 54 species (polychaetes: 27 species, bivalves: 16 species, gastropods: 6 species, echinoderms: 5 species). For almost the whole year the meroplankton was dominated by larvae of polychaetes which constituted 90.6 % of the total number of larvae. In particular Polydora ciliata and P. antennata were found in enormous numbers. Thus, about 78 % of the total number of larvae were identified as P. ciliata, followed in frequency by larvae of Mytilus edulis (8.3 %) and of Polydora antennata (6.7 %). The number of echinoderm and gastropod larvae were negligible. The observed composition of the larval plankton agrees well with that from the southern part of the Cope...