Trilateral Workshop   Report from theTrilateral Workshop on Mapping Subtidal Habitats in the Wadden Sea 16 December 2008 GKSS Research Center Geesthacht       Background In preparation of the Wadden Sea Quality Status Report 2009, the Common Wadden Sea Secretariat (CWSS), the GKSS Research Center and the ENCORA network organized a trilateral workshop on mapping of subtidal habitats on 16 December 2008. The workshop was attended by 30 experts from research institutions and administrations from the Netherlands, Germany and Denmark.   Structure and substrate of the seabed as well as the diversity and spatial distribution of marine habitats is one of the key items addressed in European directives and action plans (e.g. Water Framework Directive, Habitat Directive, Marine Strategy). A lot of mapping effort has been undertaken in the last decade on national and European level regarding the open shelf seas (e.g. the MESH project of the Interreg IIIB Programme.). In contrast, information exists only sparsely for the Wadden Sea area and different mapping methods are applied which have not yet been harmonized on trilateral level.   The objectives of this workshop were to prepare an inventory of available information and initiatives running in the Wadden Sea, to identify gaps in information, to compare the applied methodologies, to contribute to the Wadden Sea QSR 2009, and to build up a trilateral network for joint activities.   Presentations The workshop started with presentation on monitoring requirements from the Wadden Sea Plan (Targets on the Tidal Area) by Harald Marencic (CWSS) and an overview of reporting requirements from the EU Habitats, Water Framework and Marine Strategy Directive presented by Oliver Rabe (MLUR).   A trilateral inventory, presented by Ralf Vorberg, illustrated the state of subtidal monitoring at several sites in the three countries (see map, DK to be included). More than 10 institutions are involved in ongoing monitoring or research projects using side-scan sonar and multi-beam echo sounding in combination with various ground truthing methods. He concluded that there is quite a lot of data available, however, for a more detailed analysis, a further update of the inventory is necessary. He also suggested to prepare a trilateral map of survey sites by compiling more detailed stations data in a GIS project.   In presentations by Dietmar Bürk (GKSS, multibeam seafloor mapping activities), Peter Holler (Senckenberg, Acoustic Mapping of Sublitoral Habitats in the Lower-Saxony Wadden Sea), Ronnie van Overmeeren, (Deltares, Acoustic habitat and shellfish mapping and monitoring in shallow coastal water), Jeroen Jansen (IMARES, Subtidal monitoring programs on bivalve distribution in the Netherlands) and by Christian Reimers (LANU, Roxanne sediment monitoring), recent experiences with various methods of mapping the seabed and various subtidal habitat maps were presented.   Conclusions and follow up Compared to the QSR 2004, more information on subtidal habitats is now available for QSR 2009 from various projects. However, there are only few operational subtidal monitoring programs in the Wadden Sea. Regular subtidal blue mussel monitoring schemes are carried out in the Western Dutch Wadden Sea (by dredge sampling and side scan sonar) and the Danish Wadden Sea (by dredge sampling), whereas the LANU program is the only operational seabed mapping program using acoustic methods. The workshop illustrated that acoustic methods are suitable to detect biogenic structures such as blue mussel beds and oyster beds or other benthic habitats such as Lanice fields or specific dense bivalve occurrences, as well as sediment characteristics (sediment types, hard substrate, rocks). These experiences should be used when developing monitoring strategies for the Wadden Sea. This should be done in a coordinated way and building on the experiences from the MESH project and the ICES working group on habitat mapping. On the other hand, more specific guidance is necessary to define what kind information for specific features (e.g. morphological and bathymetric characteristics, abiotic structures, benthic habitats, mussel/oyster beds) is required, and at which spatial and temporal scale. In general, a linkage of these features to the monitoring and reporting requirement of the Wadden Sea Plan and the various EU directives can be made. However, because of difference in definition of the EU habitat types “sandbanks” and “reefs” in the three countries, it was also suggested that a common understanding should be developed by the three countries how to handle these differences in the Wadden Sea. Finally, the workshop agreed on follow-up activities with regard to the completion of the trilateral inventory of subtidal mapping activities, the preparation of the QSR thematic report on subtidal habitats (lead authors Ralf Vorberg and Frouke Hofstede-Fey), and the establishment of a network to carry out joint activities such as standardization of methods, intercalibration exercises, and workshop on specific issues. These activities should also be used to enhance the integration of experiences from outside the Wadden Sea (North Sea countries, ICES, MESH project).   Further information: Harald Marencic marencic@waddensea-secretariat.org