Zooplankton, zoobenthos, and bottom sediments as related to pollution and water exchange in the Oslofjord

Abstract

1. Increasing attention has been paid to pollution and oxygen shortage in the Oslofjord. Recently, a number of investigations were carried out (1962 to 1966) in cooperation with the Norwegian Institute for Water Research. The present article summarizes a few of the major results of some of these investigations, which are based on plankton samples (vertical hauls with a Nansen closing net), zoobenthos and hyperbenthos samples (towings along the bottom with Beyer's toboggan), and sediment cores (Moore & Neill corer). 2. Aglantha digitale and Rathkea octopunctata were found in greatest numbers in the most heavily polluted areas, where bottom water and sediment were generally anoxic and azoic. 3. Spionidae, Hesionidae, and Nudibranchia thrived in polluted areas when these were not anoxic. The remaining of the benthos components compared occurred primarily in water of better quality. A consistent and distinct ranking order was found for all these components. 4. In areas where no bottom fauna was found, and in transitional zones, black or dark layers in the sediment indicated various degrees of oxygen insufficiency. 5. Combinations of toboggan towings and coring surveys provide a useful basis for classifications. 6. Most remarkable differences (variations) were recorded in the successive years of the survey. © 1968 Biologischen Anstalt Helgoland.