S. van Heteren

Benthic Habitat Variations Over Tidal Ridges, North Sea, The Netherlands

Marine ecosystems on continental shelves endure an increasing burden of human activity offshore, and the impacts on benthic habitats are not well known. An improved understanding of how benthic habitats vary in relation to substrate types and seabed features is therefore essential to both scientists and offshore developers. This case study shows that marine habitats over two tidal ridges in the North Sea vary from low-density/low-diversity communities on the well-sorted sandy crests of ridges to high-density/high-diversity communities in the poorly sorted muddy, gravelly sediments in the adjacent troughs. On sandy continental shelves, including the Netherlands Continental Shelf (NCS) in the North Sea, tidal bedforms occur of different spatial scales, such as sand banks (tidal ridges), sand waves, and megaripples. Marine habitat maps reveal that benthic habitats vary spatially on continental shelves in relation to seabed morphology, water depth, and sediment composition. The different morphological elements of tidal ridges are expected to accommodate different benthic habitats. Some tidal ridge areas in the North Sea are nominated to become marine protected areas, but are also attractive for their marine aggregates and may be designated in part as mining areas. Due to their composition and shallow water depths, tidal ridges are also suitable locations for the construction of offshore wind farms. To date, the characteristics of relatively inaccessible seabeds are too poorly understood to explain the effects of physical parameters on benthic communities. Therefore, it is important to expand our understanding of benthic habitat variations associated with tidal ridges, for the benefit of both science and offshore development.

Beach Barriers and Estuaries of the Western Netherlands

The coast of the Netherlands is dominated by barriers situated in front of a 50- to 100- km-wide, low-lying back-barrier area of heavily populated, reclaimed and cultivated tidal flats, estuaries and marshes. In the south, beyond Belgium, the barrier is connected to the mainland of Cap Blanc Nez of northwestern France. In the Netherlands, it follows the overall morphology of the Pleistocene subsurface as it connects the watersheds of the Late Weichselian drainage systems. Although the present morphology of the Dutch coast is strongly modified by tides and waves, first-order features, such as the change in strike from almost S-N in the west to almost W-E in the north, are completely defined by the Pleistocene morphology. Farther east, the barrier continues in German territory.