The meiobenthos of subtidal sandbanks on the Belgian Continental Shelf (Southern Bight of the North Sea)

The Belgian Continental Shelf (BCS) is characterized by a set of isolated subtidal sandbank systems, which greatly increase the habitat heterogeneity of the area. The meiobenthos of these sandbanks was investigated during 1997 and 1998. In total, 10 sandbanks have been sampled, belonging to three different geographically isolated systems: the Flemish Banks, the Hinder Banks and the Zeeland Banks. No obvious differences in sedimentological characteristics between the sandbanks were found, but biologically some differences could be detected. The more offshore Hinder Banks had the most diverse meiobenthos, while the Flemish Banks harboured the lowest number of meiobenthic taxa. Seasonal and regional differences in terms of densities are a result of a coupling with the primary production in the water column, with October showing highest densities and the offshore Hinder Banks harbouring lowest densities. The meiobenthos on the sandbanks was less dense (450-500 ind. 10 cm(-2)) than that in the deeper channels between the sandbanks (1250-1600 ind. 10 cm(-2)). These differences were attributed to high hydrodynamic stress around the sandbanks, preventing phytoplankton from reaching the sandbanks. Moreover, higher current speed above the sediment increases the risk for the meiobenthos of being eroded or suspended during storms. Four different communities could be identified. These did not reflect the geographical position on the BCS but seem to be influenced by local differences in sedimentological characteristics within sandbanks and sandbank systems. These sedimentological differences influenced the taxon diversity as well. Sediment preferences for less abundant taxa were investigated in several ways, and results indicated that sediments with a median grain-size were poor in terms of densities and number of taxa, while coarser sediments were richer in taxon diversity. Sediments with a median grain-size between 300-450 mum were rich both in terms of diversity and density, while sediments with a median grain-size of >450 mum still showed high diversity, but lower densities. (C) 2000 Academic Press.