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Prosjektleder Mats Walday Siden 2001 har tilstanden i Ytre Oslofjord blitt overvåket i regi av Fagrådet for Ytre Oslofjord. Undersøkelsene gir informasjon om forurensende tilførsler til fjordområdet og om miljøtilstanden på bunnen og i vannmassene. Hovedvekten er på beskrivelse av tilførsler og effekter av næringssalter. Overvåkingen har i perioden 2007-2018 vært utført som et samarbeid mellom NIVA og Havforskningsinstituttet. Denne rapporten oppsummerer og drøfter resultater fra overvåkingen i perioden 2014-2018, også i forhold til andre relevante undersøkelser og tidligere overvåking i de samme havområder. Sist i rapporten er det et det også et kapittel med spesialtema om vannsirkulasjonen i Drammensfjorden.

People are dependent on the ocean and coasts and their resources for their survival and well-being. Coastal ecosystems of the Nordic countries, such as kelp forests, blue mussel beds, eelgrass mead ...

A test deployment of a time-lapse camera lander in the deep Oslofjord (431 m) was used to obtain initial information on the response of benthic fauna to macroalgal debris. Three macroalgal species were used on the lander baited plate: Fucus serratus, Saccharina latissima and Laminaria hyperborea and observed during 41.5 hours. The deep-water shrimp Pandalus borealis were attracted to the macroalgae rapidly (3 min after the lander reached the seafloor), followed by amphipods. Shrimp abundances were significantly higher in areas covered by macroalgae compared to the adjacent seafloor and the number of shrimp visiting the macroalgae increased with time. Amphipods arrived 13 hours later and were observed mainly on decaying L. hyperborea. The abundance of amphipods on L. hyperborea increased rapidly, reaching a peak at 31 h after deployment. These initial observations suggest that debris from kelp forests and other macroalgal beds may play an important role in fuelling deep benthic communities in the outer Oslofjord and, potentially, enhance secondary production of commercial species such as P. borealis.

Mapping the seabed along the Norwegian coast is costly and time consuming. Hence, finding a modeling method to separate rocky seabed from other substrate types will provide digital maps that may be used to develop cost-effective sampling designs to predict species and habitat distribution. Our approach was to use geophysical data that were quantitative and objectively defined, generalized additive models (GAMs), and Akaike information criterion (AIC) to develop statistical models and select among them. We found that slope, terrain curvature, wave exposure, and depth predicted rocky seabed occurrence with a high degree of certainty.

Eutrophication is one of the most serious environmental problems in the Skagerrak, and climate change may increase eutrophication in the future. This study focused on the effects of eutrophication and climate, and the interactions between these 2 factors, on biodiversity in rocky bottom communities on the outer Skagerrak coast. Monitoring data from the period 1990 to 2010 including macroalgae, sessile fauna and physical and hydrochemical data were analysed. In total, 45% of the total variance in the communities could be explained by physical factors and factors related to climate and eutrophication. The most important factors regulating species richness, diversity and community structure were wave exposure level and other factors varying with depth and biogeographical region. The benthic ecosystems were overall dominated by perennial and annual algae and rich communities of sessile macroinvertebrates. Climate variation and eutrophi- cation variables had small but consistent impacts on the communities. Periods with high particle concentrations and with extreme temperatures negatively impacted benthic diversity. The responses to nutrients were variable and dependant on season and species. In January, when mea- surements best reflect available nutrients in the system, the species richness and diversity responses were concave, with the greatest richness and diversity in periods with intermediate nutrient concentrations. This pattern may indicate that our communities were in an elevated eutrophication state in periods with high nutrient concentrations and in the enrichment phase in periods with low concentrations. The study highlights the importance of regarding multiple stres- sors in combination and indicates that climate change may decrease benthic diversity in the Skagerrak in the future.

A method used in to estimate uptake of hydrophobic pollutants in marine hard bottom organisms is described. Radio-labelled toxicants (14C-PCB77 and 14C-BaP) were used in a closed continuous-flow system without making use of solvents. Concentrations of PCB77 and BaP in the water were relatively high and stable during the experimental periods (14 days). The experimental set-up gave a satisfactory dispersion of the toxicants in the water and the use of radiochemicals made analyses quick and inexpensive. Algae (Fucus vesiculosus) and mussels (Mytilus edulis) were exposed to the toxicants and uptake was principally rapid and significant. Algae exposed to PCB77 reached a steady-state level within 24 h. No steady-state level was observed for BaP during exposure. Mussels showed an approximately linear uptake rate with no steady state observed for either of the toxicants. Organisms moved to a clean environment showed no reduction in PCB77 content. For BaP a slow depuration rate was observed. The rapid uptake of PCB and BaP by the organisms, and the accumulation and retention of the substances in the tissue for a long time, may result in a considerable pool of toxicants stored in these organisms.

Unintentional effects of the antifouling agent tributyltin (TBT) have been discovered in marine gastropods as the induction of male sex characters in females, known as imposex. The occurrence of imposex in dogwhelks (Nucella lapillus) was investigated in 41 populations sampled in 1993–1995 along the Norwegian coast. A method for quantification of organotin species using gas chromatography and atomic emission detection (GC-AED) was developed. Some degree of imposex occurred in almost all populations of dogwhelks studied, except in four from Northern Norway. The concentration of organotin compounds in the gastropods from the unaffected populations was below the detection limit (7 ng Sn/g d.w.). The concentration of TBT in dogwhelks from affected populations was in the range 48–1096 ng Sn/g d.w. A positive relation between the concentration of TBT in dogwhelks and the degree of imposex was found.

Three years’ investigations of the shallow water communities at 30 different rocky shore sites in an estuary in southeast Norway were carried out during 1980–1982. The flora was mostly poor, possibly due to a combination of fresh water exposure, industrial and sewage outlets. The aim of these investigations was to establish the environmental status of the estuary prior to huge outlet reductions in 1989/90. Later reinvestigations during 1992–1994, following a significant reduction of titanium dioxide wastes and building of a new chemical sewage treatment plant have shown an improvement of the macroalgal and benthic animal communities. In the formerly most polluted area, the number of benthic taxa has increased since 1980–1982 by 50–350% in 1992–1994.