Variations in the mussel population of the Dutch Wadden Sea in relation to monitoring of other ecological parameters

Abstract

The pattern of distribution of intertidal mussel beds is relatively constant over a number of years although their surface area can vary greatly. The abundance of mussels shows much greater fluctuations. In the western part of the Dutch Wadden Sea, west of the Terschelling tidal divide, the amount of mussels on natural beds fluctuated between 1 and 24 million kg fresh weight during the years 1949 to 1988. In the eastern part of the Dutch Wadden Sea the biomass varied between 5.5 and 180 million kg. The influence of the mussels on the ecosystem therefore can be very different between years. When many mussels are present the whole watermass can be filtered every few days. In years with few mussels present the filtering may take one month. It is argued that monitor programmes for a.o. nutrients, chlorophyll and growth rates of benthic organisms are of limited value if there is no indication about the total amount of mussels in the area.