Distributional and seasonal patterns of ctenophores in Malangen, northern Norway

Abstract

Annual cycles of abundance of the ctenophore species Bolinopsis ~nfundibulum and Beroe cucumls wel-e studied in the Malangen fjord, northern Norway, during 1992. The seasonal dynamics were characterized by alternating abundances of the 2 species A biomass increase of B infundibulum occurl-ed in April and May, I-eaching a peak of 2 to 7 m1 m-.' wet volume in the surface layers in summer. The specles started to reproduce in the inner part of the fjord, and then propagated throughout the entire fjord system. Length frequency distributions indicated that B. infundibulum were reproducing continuously dunng the summer months. Biovolumes of B. infundibulum decreased in August, leaving a small number of individuals (<l ~ n d . per 5700 to overwinter in the water column. Small individuals of B. cucurnls occurred in the surface layers in spring B~ovolumes of this species were low during summer, but increased in the fall, and a large overwinterlng population (2 to 6 m1 m ' ) was present in the deep b a s ~ n s of the fjord (below 200 m) from September to April. The calculated predatory impact of B. cucunlls on B. ~nfundibulunl Increased during summer (from 6 to 501%)), and contr~buted to the autumn decrease in volume of R infundibulun~. The tvintelpopulation of B, cucurnls would be short of food ~f ctenophores were the only prey Poss~ble mechanisms contnbutlng to the observed patterns are discussed.