|Monitoring the invertebrate benthic fauna in the Dutch sector of the North Sea 1991 - 2005: an overview|
|Daan, R.; Mulder, M. (2009). Monitoring the invertebrate benthic fauna in the Dutch sector of the North Sea 1991 - 2005: an overview. NIOZ-rapport, 2009-5. NIOZ: The Netherlands. 20 pp.|
|Part of: NIOZ-rapport. Netherlands Institute for Sea Research (NIOZ): Texel. ISSN 0923-3210, more|
In the framework of ‘BIOMON’, a national program for biological monitoring of marine waters, the invertebrate benthic fauna of the Dutch Continental Shelf (DCS) has been monitored from 1991 onwards. The monitoring is based on a boxcore sampling program yearly carried out in spring at 100 stations on the DCS. The aim is to generate a time series that can form a basis to detect possible trends in the development of the
fauna in different areas within the DCS. From the very beginnng it became clear that in the fauna of the DCS four clusters could be discerned that are geographically well defined: the Dogger Bank, the Oyster Ground, the southern offshore area and the coastal area. At the community level there were no trendwise changes over the period of monitoring. Species diversity was consistently highest at the Dogger Bank and in the Oyster Ground, on average twice as high as in the southern offshore and coastal areas. Faunal densities were generally the highest in the Oyster Ground. The highest biomass values were found in the coastal area, due to the presence of banks of bivalves (Spisula subtruncata and Ensis americanus). At the species level a few trends were observed: the disappearance of the polychaete Aricidea minuta from the DCS around 2000 and a dip in the densities of the brittle star Amphiura filiformis in the Oyster Ground during the second half of the nineties. A rather strong decrease of silt contents of the sediment in the latter area after 2001 was not reflected in a change in the abundance of one or more common species. A comparison of the monitoring data with data collected in the period 1975 – 1981 appeared to be possible for only a few (mainly mollusc) species in the Oyster Ground, but indicated that the gastropod Turritella communis has strongly decreased since those years whereas there was a significant increase in the abundance of several small bivalve species.