In situ ecological quality status in the Kosterhavet National Park (Skagerrak, North Sea): a 100 year-perspective

Abstract

The Koster Trench is the deepest part of the Kosterfjord located in the Skagerrak at the north-west coast of Sweden. In 2009 the Kosterfjord was included into the Marine Protected area Kosterhavet National Park characterized by high biodiversity and a presence of cold-water coral reefs dominated by Lophelia pertusa. The cold-water coral reefs show signs of deterioration and are known to have a much wider distribution during the past. In this study we investigate the temporal variability of the Ecological Quality Status (EcoQS) using benthic foraminifera and sediment geochemistry from a sediment core collected in the Koster Trench together with available hydrographic timeseries and meteorological data. We found that the EcoQS for TOC, metals, and foraminiferal indices suggest high to good ecological status close to natural background levels (reference conditions). However, arsenic (As) content in the sediment has been rising steadily over the period ∼ 1880–2009. Given this pollutant will continue to rise further, it may pass a threshold after which it becomes toxic to the benthic organisms, reaching intermediate EcoQS as it was shown by previous studies. Multivariate statistics performed on foraminiferal data identified three assemblages characterising the record: 1) Stainforthia fusiformis group at ∼ 1880–1940; 2) Bulimina marginata, Cassidulina laevigata and Hyalinea baltica group between ∼ 1940–1985, and, finally, 3) Stainforthia fusiformis and Textularia earlandi group at ∼ 1985–2009. The benthic foraminifera and sediment geochemistry suggests that a decrease in coastal upwelling due to positive NAO together with an increase in freshwater inflow from 1979/1980s; changes in phytoplankton community composition in late 2000s, and trawling activity shifted to the deepest fjord basin from 2009, all together likely have caused a shift towards more opportunistic foraminiferal species with an omnivorous feeding strategies and tolerance of physical disturbance.