Documentation of sites of intertidal blue mussel (Mytilus edulis L.) beds of the Lower Saxonian Wadden Sea, southern North Sea (as of 2003) and the role of their structure for spatfall settlement

Helgol Mar Res (2008) 62:177188 DOI 10.1007/s10152-008-0106-y

ORIGINAL ARTICLE

Documentation of sites of intertidal blue mussel (Mytilus edulis L.) beds of the Lower Saxonian Wadden Sea, southern North Sea(as of 2003) and the role of their structure for spatfall settlement

Marc Herlyn Gerald Millat Birgit Petersen

Received: 10 April 2007 / Revised: 17 December 2007 / Accepted: 8 January 2008 / Published online: 5 February 2008 Springer-Verlag and AWI 2008

Abstract Field surveys (dating back to 1950) and aerial photograph series (dating back to 1966) were evaluated to determine sites of intertidal blue mussel (Mytilus edulis) beds at the Wadden Sea coast of Lower Saxony. Maps were prepared indicating sites of blue mussel beds during the last decades. A table gives additional information on the presence (or absence) of blue mussel beds at each site at the time of large-scale surveys. Altogether 187 sites of M. edulis beds were recorded in the investigation area. In spring 1996, there were still only 19 sites where mussel beds still occurred, although at 51 sites residual mussel-bed structures were present, e.g. shell bases of former beds or protruding patches (which had been occupied by M. edulis before the beds vanished) and open spaces. At that time, the majority of the sites contained neither mussel beds nor mussel-bed structures. The analysis of recent data con-

Wrmed that mussel larvae have preferred to settle in sites of present mussel beds and sites with bases of former mussel beds. There was no preferential selection of one of these categories (settled beds vs. shell bases). On the other hand, the presence of mussel beds or mussel bed structures is not obligatory for settlement, because sites without those structures were also re-settled by the spatfall in 1996, even though on a smaller scale.

Keywords Mytilus edulis Blue mussel bed Spatfall Site documentation Wadden Sea of Lower Saxony Aerial photography Field investigation

Introduction

The decline of the intertidal blue mussel (Mytilus edulis) beds at the coast of Lower Saxony from the mid-1980s (Obert and Michaelis 1991; Michaelis et al. 1995; Herlyn 1996, 1999; Herlyn and Michaelis 1996; Zens et al. 1997) to the mid-1990s (Herlyn and Millat 2000; De Vlas et al. 2005) was examined by extensive evaluation of the data sources on the...