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Historical benthos data compared for WFD purposes

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Gutow, L. , Boos, K. , Buchholz, C. and Buchholz, F. (2005): Historical benthos data compared for WFD purposes , MarBEF and LargeNet Workshop on Long Term Data Set Networking, 3-4 March 2005, Helgoland, Germany. .
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Abstract:

The composition of macrozoobenthos was used as an indicator for the evaluation of the water quality around Helgoland (German Bight, North Sea) according to the European Union Water Framework Directive (EU-WFD). Changes in the species community over the past 150 years were assessed from an extensive literature survey for the island of Helgoland as well as the adjacent Tiefe Rinne - a depression of the seafloor down to 60 m depth. Water quality, as far as macrozoobenthos is concerned, was presently found to be moderate for both investigated areas.Within the time period reviewed, species richness was highest in the Crustacea, Mollusca and Polychaeta. Due to their conspicuousness these groups were considered robust towards methodical irregularities making them reliable indicators of long-term changes in faunal communities. Consequently, further analyses were performed exclusively on these groups. The results revealed major changes over time issuing from substantial loss in species richness as well as from substantial exchange of species. The Sørensen-Index revealed fairly low similarities ranging from about 30 to 55 % for Helgoland and from around 40 to 53 % for the Tiefe Rinne .Changes in abundance over time are very difficult to assess for various reasons. One major problem is that in most historical publications, quantitative information is described in words rather than numbers and therefore implies a high amount of subjectivity with regard to both the author and the reader. Yet, to make data comparable, all quantitative information available was ranked by common sense according to 6 different categories of abundance . Referring to the conspicuous taxa mentioned above, the results for both locations indicated a general trend of decrease in abundance over time in? 4.1 to 10.0 % of the species.To overcome the problem of missing quantitative data, the authors created a working basis leading to reasonable results, which could even be confirmed by some case studies, eg. the extinction of the European Oyster Ostrea edulis in the vicinity of Helgoland. The proposed method for a quantification of historical data was commonly accepted. It provides an efficient and fairly objective approach to assess changes in faunal associations. With respect to the difficulties mentioned above, further development and the reconfirmation of accuracy of the proposed method was recommended among the participants of the workshop. This was particularly emphasised in view of the urgent request of applying the proposed method not only to benthic data but also to the historical plankton data sets of Helgoland roads.

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