Zoobenthos responses to eutrophication of the Dutch Wadden Sea

Abstract

During the last few decades nutrient concentrations in the Dutch coastal waters have increased significantly. Values observed for rates of primary production as well as for concentrations of chlorophyll and for particulate organic matter have been higher during recent years than estimates from earlier periods. Thus more food will have been available for herbivorous benthos during recent years. Both biomass and annual production of the macrozoobenthos living on the tidal flats in the western part of the Wadden Sea doubled during the 1970 to 1984 period. More than half of the species contributed to this increase. In the species studied in most detail, Macoma balthica, both reproductive success and growth rate increased significantly during the 15-year period. Though a causal relationship between simultaneous increases of nutrient levels, primary production and secondary production cannot be proved, such a relationship seems to be natural. So far, obvious detrimental effects such as mass mortalities from lack of oxygen appear to be rare in the well-mixed Wadden Sea.