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Acoustic kelp bed mapping in shallow rocky coasts - case study Helgoland (North Sea)

Figure 1 Aspect of the kelp forest off Helgoland. The main structuring species is the brown alga Laminaria hyperborea which grows to a length of approx. 1-2 m and provides shelter and substrate for many other species. Foto: C. Wanke, Biologische Anstalt Helgoland.

Kelp beds are named after their habitat structuring organisms which are perennial brown macroalgae of several metres length, living submersed in the light penetrated zone of temperate and polar rocky shores (Fig. 1). Kelps provide substrate, food and protection for hundreds of different marine fishes, invertebrates, or other macroalgal species. A change or loss will have drastic consequences for coastal ecosystems.

In recent years worldwide reports of changing kelp beds have been published (Japan: Kirihara et al., 2006, Norway: Moy et al., 2003, France: Cosson, 1999, Australia: Australian Marine Conservation Society www.amcs.org.au/). In Europe, including Helgoland (Gehling & Bartsch, submitted), there is evidence of a biomass decrease and/or change in depth distribution of some species. As the marine protected area off Helgoland is the only rocky area within the southern North Sea, this habitat is extremely important. Spatial information on the extent of the prevailing kelp beds is urgently needed as a baseline from which to judge future changes. This led to the current case study.