Publication Date:
2022-01-13
Description:
More than 100 years ago C.G.J. Petersen {1911) analyzed marine communities in the Scandinavian waters. He delivered broad and detailed information on the organisms living in the sea at that time. His studies were extended by Pearson et al. in 1984, which re-assessed the macrobenthic communities in the Kattegat and examined changes between the two time periods. The present status of these macrobenthic communities and alterations since the 1900's were determined and analyzed in this thesis. Therefore historical stations in the Kattegat were resampled at nine stations in 2010, 2011 and 2012 along a north-south transect. Abundance, Biomass, Diversity and number of genera were determined for every station respectively for the individual years. For the comparisons of benthic communities with these from former times only limited data was available. General community descriptions, mean biomass data and rank biomass data from Petersen {1918) and Pearson et al. {1985) were available. Recent data was adjusted to enable comparability. Multivariate analyses were used to detect changes of the community structures. Supplementary to the historical community analysis influences of different abiotic factors on recent communities were examined. One part of the factors were measured during the research cruises (salinity, oxygen concentration, pH and temperature), the other biotic and abiotic factors were obtained from different literature. Thereupon factors were correlated to the actual benthic communities if possible by regression analysis otherwise by general evaluations. The total biomass of organisms in the Kattegat declined of about one half since the 1900's. The
highest recession was found in the northern and western area since the 1900's and in the southern and eastern area since the 1980' s. Biomass decreases were caused by increasing numbers of small opportunistic species, especially echinoderms and molluscs. A life-trait analysis revealed increasing numbers of tolerant species (especially suspension-feeders) since the 1900's. Large fragile species like Echinocardium cordatum, Brissopsis lyrifera and Arctica islandica disappeared to a great extent. Also many species which are known to benefit from high nutrient conditions disappeared, most probably due to the increase of low oxygen conditions. One species increased its abundance and biomass extensively, especially in the northern Kattegat: Amphiura filiformis. Community structures as defined by Petersen in 1911 were not detected anymore. It was possible to show that the benthic communities were significantly correlated with a biotic factors in the assessed time period. The main factor shaping the communities in 2010-12 was proven to be the oxygen concentration at the seafloor. In recent years most probably synergistic effects of eutrophication, fishing activity and climate change caused once more a regime shift of the macrobenthic communities of the Kattegat.
Keywords:
Course of study: MSc Biological Oceanography
Type:
Thesis
,
NonPeerReviewed
Format:
text
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