|Macrozoobenthos on an intertidal mudflat in the Danish Wadden Sea: comparisons of surveys made in the 1930s, 1940s and 1980s|
|Jensen, K.T. (1992). Macrozoobenthos on an intertidal mudflat in the Danish Wadden Sea: comparisons of surveys made in the 1930s, 1940s and 1980s. Helgol. Meeresunters. 46(4): 363-376|
|In: Helgoländer Meeresuntersuchungen. Biologische Anstalt Helgoland: Hamburg. ISSN 0174-3597, more|
Introduced species; Ensis americanus (Gould, 1870) [WoRMS]; Petricola pholadiformis Lamarck, 1818 [WoRMS]; Scrobicularia plana (da Costa, 1778) [WoRMS]; Tharyx killariensis (Southern, 1914) [WoRMS]; ANE, Wadden Sea [gazetteer]; Marine
To assess whether long-term faunal changes have occurred on intertidal flats in the Danish Wadden Sea, results of faunal surveys in the Skallingen area during the 1930s, 1940s and 1980s were compared. Since the earlier studies, two species have disappeared (Scrobicularia plana and Petricola pholadiformis) and two have invaded the area (Tharyx killariensis and Ensis americanus). This is, however, not a local event as species changes have occurred on a larger scale (Wadden Sea region). Comparison of abundance data did not provide evidence of changes from the 1930s until the 1980s. Spatio-temporal fluctuations in two dominant species, the mudsnail Hydrobia ulvae and the cockle Cerastoderma edule chosen for closer examination, could be explained by natural processes. Growth data on cockles from the 1930s and the 1980s matched perfectly. During both periods, cockles showed a much lower growth rate than generally reported from the Wadden Sea, while at the same time they occurred at high densities (>2000 ind•m−2). Intraspecific competition among cockles is suspected as being a major cause of the low growth rates. Estimates of secondary production and P/B-ratios of cockles were also in general agreement during the 1930s and the 1980s when corrected for differences in the age structure of the cockle populations. With the possible exception of Mytilus edulis, which according to some observations has extended its range along the low-water line, the present comparison failed to demonstrate long-term faunal changes caused by increased eutrophication. This results is expected to be representative for intertidal flats not exposed to direct impacts from terrestrial run-offs and waste-water discharges.