Report | December 16, 2019
Protecting the North Sea: Cleaver Bank
Cleaver Bank (Klaverbank in Dutch) extends over 1235 km2 in a transboundary area shared between the UK and the Netherlands (Fig. 1). In comparison with surrounding areas, it is home to a diverse benthic community and a wide variety of substrates, specifically gravel and dispersed rocks that originated in the last Ice Age (15 000 years ago).1 The relatively greater depth of Cleaver Bank in comparison with the surrounding area prevents the bottom from being disturbed by wave action; as a result, it is the only area in the Dutch North Sea where such an accumulation of hard substrate occurs, with around 30% of non-sedimented gravel.2 Over large areas, silt and sand have accumulated, forming ripples that follow the main water current direction and that can extend over kilometres.3
This atypical substrate and clear waters – which enable light penetration down to 30-50 m – support a high level of benthic diversity in Cleaver Bank: the highest in the Dutch continental shelf.4 The ecological value of the UK side of the area is likely to be even higher, as gravel and rocky areas also occur there.5 There is a large proliferation of crustose red algae (i.e., Lithothamnion sonderi and Phymatolithon sp.),1 as well as fauna such as crabs, worms and molluscs. Moreover, Cleaver Bank is divided in two sectors by the Botney Cut, a 60 m deep channel running from northwest to southeast that hosts harbour porpoises, minke whales, and seals, as well as white-beaked dolphins during the summer.6 Razorbills and guillemots are also found in the area, mostly during the months of April and May.7
The area qualifies as a stony reef under the EU Habitats Directive,8 as it meets the criterion of containing a considerable number of cobbles and boulders (i.e., rocks generally larger than 6 cm). As a result, the Dutch side has partially been designated as a Natura 2000 Special Area of Conservation (SAC), named Klaverbank. An OSPAR marine protected area (MPA) has also been designated, the boundaries of which almost coincide with the SAC.
A high resolution version of this report can be found here.
