Biodiversity of the benthos and the avifauna of the Belgian coastal waters: summary of data collected between 1970 and 1998

Marine biologists have intensively studied the Belgian Continental Shelf (BCS) since the early seventies. Still, much of the knowledge on the biology and ecology of the biota collected remains hidden in little accessible and 'grey' literature. A complete overview of all biota, from the plankton to the higher trophic levels, still lacks. This synthesis wants to remedy this by reviewing the knowledge on the biodiversity of the benthos and the avifauna of the BCS. To detect biodiversity patterns, literature data were collected on diversity measures of the benthos communities. Therefore, the BCS was divided into nine zones. The demarcation of these zones relies partly on geographical and partly on biological information. For each of these zones, data on species number and species richness were collected. Clear patterns in average species number have been observed for the meiobenthos, the macrobenthos and the hyperbenthos. The species number of benthic assemblages in inshore waters changes dramatically between the eastern and western end of the Belgian coast. A second gradient runs perpendicular to the coastline and involves an increasing species number and diversity offshore. A third gradient relating to depth within a zone needs yet to be confirmed. Also an offshore decrease in density has been observed for macrobenthos and hyperbenthos. Avifauna data do not confirm these patterns even though seabird assemblages offshore differ from the inshore avifauna. All observed patterns need yet to be confirmed by standardised research and monitoring, being the aim of the ongoing programme. Besides the analysis of structural and functional biodiversity data on benthos and avifauna, this synthesis also examined the knowledge on the genetic structure and the parasite fauna of fish occurring on the BCS. The limited information available on the Belgian coastal waters points at continuity between fish populations of the English Channel, the Southern Bight and the Central North Sea. Genetic differences of fish parasites have been observed in the area and may aid in addressing issues like genetic selection of the heavily fished populations