Ecological studies on the deep-water pelagic community of Korsfjorden (western Norway)

As part of a project aimed at assessing the available energy in a pelagic system and the efficiency of its transfer, monthly biomass estimates of the 23 main macroplanktonic and mesoplanktonic species have been made in Korsfjorden (Norway). Sampling was carried out over approximately 3 years (1971–1974) and results are presented as mg dry weight in a 690 m³ water column. The total annual stocks of the various species were not constant in the 3 years of sampling. Principal components analyses of the monthly stocks in each of the 3 years show striking differences in the correlation matrices from year to year. On the basis of known and supposed feeding habits, the species have been classified as herbivores, omnivores, or carnivores. The monthly biomass estimates of these groups show a consistent pattern from year to year. This, in contrast to the variable correlations between individual species, indicates that there can be considerable flexibility in the specific composition of a planktonic community without correspondingly marked effects on its trophic structure.