Samenvatting

This study aimed to get more insight into the spatial distribution pattern of the macrobenthos at the Vlakte van de Raan in relation to environmental gradients (median grain size, salinity and bathymetry). 82 samples were collected in November 2016 with a Van Veen grab using the research vessel the ‘RV Simon Stevin’. For this research, the macrobenthos of 43 samples were identified using microscopy. In addition, data were collected on the following environmental gradients: salinity, bathymetry, median grain size, mud content and TOM (Total Organic Material). The salinity was measured while collecting the samples. The sediment samples were collected as well for the calculation of TOM. Using a Mastersizer, the median grain sizes and mud content of the area were determined. Data on bathymetry was provided via VLIZ (Vlaams Instituut voor de Zee).

Most dominant species of the Vlakte van de Raan are: Nephtys sp., Magelona johnstoni, Spiophanes bombyx, Scoloplos armiger, Aphelochaeta marioni, Abra alba, Macoma balthica and Petricola pholadiformis, with Nephtys sp., Magelona johnstoni and Macoma balthica being most abundant.

The macrobenthos biodiversity was highest in the Northern part of the Vlakte van de Raan and lowest in the East as low salinity (and perhaps fluctuations in salinity) and large median grain sizes (MEDGS) is not preferable for the organisms. Overall the organisms tend to prefer to live in an area having a smaller median grain size, a higher mud content and a higher organic material.