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A growing need for food is causing increased interest for seaweed farming globally. This requires the knowledge of the industry’s effects on the marine environment. We therefore aimed to explore the communities hosted by a kelp farm compared to that of wild kelp forests. The study was performed in mid-western Norway. Kelp associated fauna were collected from farmed kelp (Saccharina latissima and Alaria esculenta), in wild kelp forests (S. latissima, A. esculenta, and Laminaria hyperborea), and from fauna traps in the water column. The study showed that the kelp farm had lower taxa abundance and richness and a lower biodiversity than the wild kelp forests. Nonetheless, the farmed kelp hosted many associated species, with communities different from what was found on ropes without kelp (i.e., in the water column). The fauna communities among the farmed kelp were more similar to what was found in the wild L. hyperborea kelp forest than to its wild counterparts. The difference between the fauna communities of ‘old’ and ‘young’ farmed kelp (grown for 3 and 7 months, respectively) was not significant, but the fauna was dominated by the isopod species Idotea pelagica in the young forest and by amphipods, mainly belonging to the genus Caprella, in the older. The study contributes to our knowledge of kelp farms’ ecological role in the marine environment, which is of importance for today’s management as well as for ensuring a sustainable future development of the kelp farming industry.

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.