Cruise report 64PE505 - ReViFES Brown Bank, Frisian Front, Borkum reef grounds Version 6

This cruise was carried out for the ReViFES project. The rationale behind this cruise and project is to find out what the scale of ecosystem services of reef structures are in the North Sea. The initial focal area was the Brown Bank, an areas west of the Dutch coast near the Dutch-UK border, characterised by a shallow sand bank (~20 m deep) flanked by deep troughs (~40 m) in an otherwise ~30 m deep region. In 2017-2019 a Sabellaria spinulosa reef was observed (van der Reijden et al. 2019; van der Reijden et al. 2021) in the eastern and western trences next to the bank. The revifes team aimed to revisit these reefs and investigate the ecosystem services provided by the reef. However, the reefs were not observed and the team could not execute the plan. Therefore, an alternative location with recent observations of Sabellaria near the Frisian Front north of Texel (unpublished data Bureau Waardenburg) was surveyed as well. Again, the observed reefs were not detected. Then it was decided to spend the last 6 research days on investigating the Borkum Reef grounds on the border of the Dutch - German continental shelf, situated approximately 20 km offshore (north) from the island of Schiermonnikoog. This site had been studied in 2020 (Witbaard et al. 2021) and 2021 (Coolen et al. 2021).