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MEPS prepress abstract   -  DOI:

Review of 50 year monitoring the macrobenthic animals on a 50-km2 tidal-flat area in the Dutch Wadden Sea

J. J. Beukema*, R. Dekker

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ABSTRACT: Macrobenthic animals living in a tidal-flat area in the westernmost part of the Wadden Sea were monitored for 50 years in succession (1970–2019) using consistent methods. About 100 papers were published on this project. We review a number of results and conclusions on observed changes and their possible underlying causal processes. The most significant changes in population sizes and growth rates of several species could be attributed to climate warming (by about 2°C), going along with increasing trends in species richness and total late-winter zoobenthic biomass. In the initial years, eutrophication (doubling of nutrients and chlorophyll concentrations) resulted in a doubling of zoobenthic biomass. The subsequent de-eutrophication after the mid-1980s was reflected only in the biomass values observed in late summer. A long-term trend in food supply for birds was not observed. Disturbances from fishery were intermittent and modest. In several bivalve species, magnitudes of production and biomass were determined primarily by foregoing recruitment variation which was mainly caused by spring abundance of epibenthic predators (shore crabs and shrimps). Their abundance increased with temperatures in the preceding winter. As contrasted to this top-down regulation, bottom-up processes apparently played only a minor role in the determination of bivalve biomass. Rarely occurring extremely high bivalve numbers resulted in reduced rates of growth and production. We conclude that the uniquely long monitoring of the tidal-flat macrozoobenthos yielded data series which not only indicated several long-term trends, but also contributed to our insight in processes underlying the observed trends. Most of the observed trends were related to climate change and eutrophication followed by de-eutrophication.