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

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2016

End date

12/31/2019

Budget

627,546 EUR

Fundings

Abstract

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.