A century of change: ecological responses to pollution, climate, and other stressors on the Skagerrak coast

In this project, we compiled a wide range of data including fish and benthic community, contaminants, hydrography, biogeochemistry, and foraminifera assemblages, in order to investigate how contaminants affect cod but also fish community dynamics on the Skagerrak coast. Sediment cores from the research area show increased accumulation rates of organic carbon throughout the time period represented by the sediment cores (i.e., since the 1920s). The data supporting this interpretation includes stable carbon isotopes of organic matter in bulk sediments as well as of benthic foraminiferal carbonate shells. The latter includes increasing abundance of opportunistic foraminiferal species and deteriorated ecological quality status moving from high/good in the older deposits to moderate, poor or bad in younger deposits depending on the severity of the impact. The temporal distribution of carbon isotopes and C/N-ratios in the sediments reflects that marine phytoplankton dominated the deposited organic matter throughout the investigated time periods. Neither of the areas had been severely polluted by heavy metals but, as recorded in other southern Norwegian fjords, maximum concentrations generally occurred between the 1960s and the 1990s. Based on 27 years of data from 8 populations of the snail species dog whelk, we show how the progressive restrictions on TBT, especially the ban in 2008, lead to a strong decrease in TBT in dog whelks. In parallel, the incidence of reproductive abnormalities in dog whelks has decreased, but with a time lag of a few years due to the long life-span of the species. As expected, we found the highest incidence of TBT and imposex close to main shipping lanes. In the fjords Frierfjorden and Eirdangerfjorden we have studied 39 year-long time series of pollution of three substances, hexachlorobenzene (HCB), octachlorostyrene (OCS) and decachlorobiphenyl (DCB , aka. PCB-209). Closure of the source of the pollution, a magnesium factory, in 2001 was expected to be followed by a rapid and large reduction in the contaminant levels in biota, but these expectations have not been fully fulfilled. Concentrations of HCB and OCS in cod decreased strongly when discharges were reduced (1975-76 og 1989-90), but there is no clear evidence of further reduction after 2001. DCB has decreased much less than the other two substances during the entire study period, and the concentrations are still >100 and >30 times the expected level in Frierfjord and Eidangerfjord, respectively. The project has resulted in a paper (in revision in the Proceedings of Royal Society B) (Ono et al. in revision) where the team investigated the potential adverse effect of three major environmental contaminants (i.e. mercury, cadmium, and HCB) to the population dynamics of coastal cod in the Skagerrak region. The study was able to find some evidence of an adverse effect of pollutant concentration, especially mercury, on the reproductive potential of the coastal cod population. Additionally, there was some regional difference in cod sensitivity to pollution with the northern region showing a stronger sensitivity than the southern region. However, pollutant concentrations have been generally declining in the region since the early 1980s but many local cod populations are still in bad shape. This suggests that cod population recovery requires complimentary efforts on fishing regulation and habitat restoration but also an increased understanding of the processes shaping local populations.

Ved hjelp av dette prosjektet har vi styrket samarbeidet mellom ulike fagfelt (marin økologi, geologi, og økotoksikologi) og institusjoner. Det hadde ikke vært mulig å gjennomføre prosjektets oppgaver uten deling av kunnskap, ekspertise, arbeid og data mellom NIVA, Havforskingsinstituttet, UiO (Institutt for geofag og CEES) og UiA (Centre of Coastal Research). Prosjektet har resultert i økende kunnskap om forurensing og dens effekter som har direkte relevans for Miljødirektoratet. Prosjektet har vist at variasjonene i torskebestanden samsvarer med variasjoner i kvikksølvforurensing, noe som støtter opp om arbeidet med Minamatakonvensjonen. Forskningen på TBT viser at myndighetenes regulering av TBT har vært effektiv, mens våre resultater på HCB, OCS og DCB i Grenlandsfjordene viser at opphør av punktkildene ikke har vært et tilstrekkelig tiltak for å føre forurensingen tilbake til et normalnivå.

Few studies attempt to quantify the effects of pollution on natural populations and species communities. Often, the available data sets are too constrained either spatially or temporally to separate the effect of pollution from other factors, such as climate and harvesting. However, along the Norwegian Skagerrak coast, an exceptional set of data makes it feasible to describe the state and the pressures of the ecosystem comprehensively in several fjord systems for almost a century. This includes: (1) beach seine data on the fish community, sampled annually at 38-100 stations since 1919, (2) data from sediment cores giving records of benthic foraminifera and environmental variables since at least 1900, (3) data on contaminants in fish and mussels from 1968 onwards, and (4) registrations of kelps and seagrass (since 1934) and complete benthic species registration (since 1990). In the present study, reseachers from different fields (population biology, environmental geology, ecotoxicology, marine ecology) join forces to analyze these data sets together. The project has four WPs: (1) Compiling and improving data, in particular, processing and analyzing additional samples from existing and new sediment cores; (2) Analyzing spatiotemporal trends of pollution (contaminants, eutrophication) in sediment cores in relation to climate and contaminant concentration in biota; (3) Modelling community and population-level responses to environmental change, which includes an analysis of cod population dynamics using state-of-the-art statistical methodology and (4) synthesis and outreach, including setting up a web site which collects existing information on the Skagerrak ecosystems and its stressors as well as organization of a discussion meeting involving stakeholders, politicians and researchers. By bringing together researchers with diverse expertise, and combining rich long-term data, this project will advance our knowledge of the impacts of pollution on coastal ecosystems.