Royal Netherlands Institute for Sea Research

Intertidal benthos

Total mean biomass in ash free dry mass per m2 of macrozoobenthos (polychaetes and bivalves) in the intertidal in the various tidal basins.
1:Marsdiep; 2:Eierlandse Gat; 3:Vlie; 4:Borndiep; 5:Pinkegat; 6:Zoutkamperlaag; 7:Eilanderbalg; 8:Lauwers; 9:Schild; 10:Lower Ems; 11:Upper Ems; 12:Dollard.

SIBES Framework

Since 2008, the intertidal macrozoobenthos of the Dutch Wadden Sea has been sampled in late summer on a 500 * 500 m grid. This was done within the framework of the Synoptic Intertidal Benthic Survey (SIBES) project. About 4500 benthos and sediment samples have been collected annually.

Over the years, large differences between tidal basins and over time have been observed. Most areas showed a dip in biomass in 2011, and a recovery in recent years, with a difference of up to a factor of 4, especially in the Vlie basin. From the 2014 and 2015 samplings, only the data from Balgzand, Pinkegat and Zoutkamperlaag have been processed. Trends between areas varied; at Balgzand, biomass values showed a steady increase, while at Pinkegat and Zoutkamperlaag it dropped in 2014 and recovered in 2015. Balgzand became the richest area of these three basins in 2015. These fluctuations in biomass, both in time and between areas, may have repercussions for the Wadden Sea as a feeding and nursery area for wading birds and fishes. The underlying mechanisms responsible for these different patterns in fluctuations are currently unclear and will be the focus of future research.


During the first 5 years SIBES was funded by the national Ocean and Coastal Research programme (NWO-ZKO), together with the gas exploration and production company, NAM and NIOZ. From 2013 onwards, sampling has been partly funded by NAM for the ecological monitoring of the gas drilling areas in the eastern Wadden Sea, and by the company Arenicola for the ecological monitoring of lugworm digging in the Eierlandse Gat. Since 2014, sample processing and data analysis has been restricted to a few areas in the Wadden Sea, financed by NIOZ (Balgzand area; blue), Arenicola (Eierlandse Gat; red) and NAM (Zoutkamperlaag, Pinkegat; yellow) respectively. Remaining samples of the other areas have been stored at NIOZ. SIBES sampling was continued in 2016 by NIOZ with the financial support of NAM and Arenicola for 1 year.