Located at the centre of the Southern North Sea, Brown Bank (also known as Brown Ridge, and Bruine Bank in Dutch) is a ridge formed by a series of large-scale sandbanks that crosses into both Dutch and UK waters. It’s a recognised area of ecological interest, due mainly to the high abundance of cetaceans and seabirds. The area is also well-known for its abundant presence of fossils dating from the Pleistocene period, such as the woolly mammoth and the straight tusked elephant.
To date, however, Brown Bank has been granted very limited protection by governing bodies. The UK side is protected for a single species (harbour porpoise), within the Southern North Sea Marine Protected Area. No such protection is in place for the Dutch side, although it qualifies for inclusion in the Natura 2000 network due to the high numbers of seabirds that it supports, particularly the common guillemot and razorbill.
Research surveys carried out in the area by Oceana in 2016 and 2017 identified 204 taxi which included nine priority species for conservation, and a range of commercially fished species, including fish for which Brown Bank provides spawning or nursery habitat. ROV dives were used to collect data, discovering a variety of surprising features about the area.
The most noteworthy discovery was the presence of biogenic reefs formed by ross worms (Sabellaria spinulosa), a sedimentary polychaete, which live in a tube made of shell fragments and coarse sand, cemented together with mucus. These biogenetic reefs covered a total area of 1,023m2 on the Dutch side of Brown Bank, and hosted a variety of associated species, including various crabs, common dragonet, and lesser spotted dogfish. The biogenetic reefs have almost entirely disappeared from Dutch waters, and ross worm reefs were previously thought to have been long-extinct in the area.
The three S. spinulosa reefs discovered were observed on the lower part of the bank slope or in the troughs of the bank between 38m and 45m. They were mostly found in the troughs between sand ripples, with few observed on the surface of the ripples. This suggests that the troughs serve as suitable habitat for the Sabellaria settlement, perhaps providing some degree of refuge from the intensive benthic fisheries in the area. So far, the reefs have only been located on the Dutch side of the bank, however it is highly probable that they also exist on the UK side, given the homogeneity of the substrate across the area.
The findings of four dead individual European flat oysters acted as a reminder that this species was once abundant throughout the North Sea, until overexploitation led to a drastic decline. The scarcity of the oyster beds has caused a loss in the provision of hard substrate, habitat and food for other species, hence the species being a strong focus of conservation efforts. The Netherlands and the UK are both contracting parties to the Convention for the Protection of the Marine Environment of the North-East Atlantic (or OSPAR), requiring them to protect and restore flat oyster beds.
Intensive overfishing during the 1970s and 1980s has caused the deterioration of the sole and plaice species, both listed as priorities in the UK biodiversity plan. Cod has also been exploited by fishing but is making a slow recovery. Two small cetaceans were identified during the research sampling, likely to be harbour porpoises. Cetaceans inhabiting the North Sea also face a wide range of threats from human activity in the area, including incidental catches in fisheries, overfishing of main prey species, the bioaccumulation of pollutants, and underwater noise disturbance.
Scientists have long considered the protection of Brown Bank to be a priority, with studies highlighting the value of the area for seabirds and for marine mammals. Despite this, only limited protection has been enacted by the UK and the Netherlands. Benthic fishing involves trawling through the ocean sea bed, causing immense damage to the biogenic reefs. In fact, the ROV dives discovered the seabed was noticeably altered in some parts. These impacts are categorised as either geotechnical (physical penetration of the sea bed) or hydrodynamic (mobilisation of sediments). Currently, the only remaining reefs are protected by the formation of the sand waves in which they reside. However, it is plausible that reef reformations could return to areas where they have previously been destroyed by demersal fishing pressures.
Unfortunately, the Dutch North Sea is a very crowded space with many competing special interests, hence the conservation of marine ecosystems has not been a priority of the Dutch government. In its National Water Plan 2016-2021, the government lays out its vision for a ‘development-based approach’ to the North Sea. Under this vision, protection of the marine environment is presented as a ‘spatial challenge’ in the face of a long list of priority activities that include oil and gas extraction, CO2 storage, shipping, renewable energy, sand extraction, and defence.Meanwhile, plans for a new wind farm, set to overlap where the formations of the reefs occur, will create a new challenge for the areas ecology.
According to Oceana, the unexpected discovery of biogenic reefs in Brown Bank demonstrates how benthic habitats and communities in the area have not been adequately studied, and that such surveys should be prioritised. Given the current heavy intensity of human activities in the area and the plans for future development, Oceana says that it is imperative that the marine biodiversity of Brown Bank be properly assessed, and appropriately protected, before it is too late.
On 31 May, the environment secretary Michael Gove announced the ‘blue belt expansion’, protecting marine life by creating 41 new conservation zones. The expansion is very welcome news, protecting an additional 12,000 square km of marine habitat.
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