Long-term development of biomass of intertidal macrozoobenthos at Piet Scheve Plaat (Dutch Wadden Sea)

The monitoring of biomass of intertidal macrozoobenthos is part of a Rijkswaterstaat Biological Monitoring Program started in 1989 to get information about the present situation and about long-term development of biological parameters. The Piet Scheve Plaat flat in the Wadden Sea is one of the sampling locations in Dutch coastal waters. Sampling took place along three transects, two of them aboven and one below NAP. In the study area no temporal trend of the total biomass was found. This correlates with the fact that no influence of freshwater and nutrients input of Lake Lauwers and Lake IJssel could be detected by measuring the primary production (indicated by the chlorophyll a content of the water which did not show a trend). Lance conchilega reacts positive to mild winter temperatures (1988-1990) its biomass increased significantly in transect 3 of this period. In the same period Macoma balthica's biomass decreased due to the loss of weight during the warm winters and the resulting small rate of reproduction success. Cerastoderma edule showed a decrease of biomass in the last three years probably due to the same reason.