Ship-based mapping of protected seafloor habitats and anthropogenic stressors in a very shallow coastal environment: Spatial data integration in a marine protected area offshore Sylt (North Sea)

Area-wide hydroacoustic mapping in coastal environments is a time-consuming and cumbersome task due to the limited swath width of most devices, especially in shallow waters. At the same time, these environments hold important functions for coastal ecosystems, are subject to intensive anthropogenic use, and are characterized by dynamic and complex geomorphological interactions of waves, currents, and tides. We presently investigate the seafloor geomorphology of a marine protected area in the eastern North Sea based on a combination of own archived hydroacoustic data, hydrographic single-beam survey data, and fishing vessel position data. The research area is located within 12-nautical miles from the coast, covers approx. 1,200km², and is characterized by water depths between 12 and 18 m. The topography of the seafloor is relatively flat and dominated by mobile sands although gravel and hard substrate (boulder reef) environments commonly occur throughout the area and are protected under the EU Habitats Directive. The properties and spatial distribution of these habitats remain currently unknown, despite the fact that the area hosts intensive fisheries with bottom-contact gears and one of Europe’s largest marine sand extraction sites. Our results show that the integration of different data sources allows an effective assessment of essential habitat parameters, natural seafloor processes, and anthropogenic stressors. Against this background, a strategy to more closely survey and/or monitor specific areas can be devised in order to better protect seafloor habitats and to mitigate human impacts on coastal ecosystems.