Monitoring of the Outer Oslofjord 2014-2018. Benthos Surveys in 2016. Technical report

Summary

Benthic investigations in the Outer Oslo fjord in 2016 included surveys of hard bottom flora and fauna in the littoral zone (quantitative quadrat registrations) at 15 stations. The investigation also included determination of the lower growth limit (depth) for a selection of up to 9 species of macroalgae at 12 stations. I addition semi-quantitative registrations of hard bottom flora and fauna in the littoral zone, financed by Borregaard AS, was conducted at 4 stations. Results from the registrations done for Borregaard is presented in a separate note. Using the MSMDI index (Multi Species Macroalgae Depth Index), 6 stations were classified to be in “good” ecological condition, 5 stations in “moderate” condition and one station (G14) was classified to be in “poor” ecological condition. In 2014, the introduced species pacific oyster (Crassostrea gigas) was registered at 6 station, in 2016 it was registered at 11 stations. High prevalence of diatoms- and blue-green algae and the opportunistic greenalgae, Ulva intestinalis, in the littoral zone at 3 stations (G9 by Sandefjord, G10 by Stavern and G21 by Hvaler), are indications of eutrophication. However, there are no obvious connections between species composition at the stations, and nutrients measured in the surface water at nearby stations.