Seabed Habitat (Habitat Directive) - FR5302008 'Roches de Penmarc’h' - FR004031

Mapping of the Natura 2000 site « Roches de Penmarc'h » was jointly performed in the framework of two different actions: (i) the Natura 2000 convention for Brittany and (ii) the Interreg Area MeshAtlantic Project. It is based on the interpretation of various types of data from a number of surveys carried out between 2011-2012 both in the intertidal and subtidal zones. Additionally the seabed « Carte G » from the French hydrographic survey (SHOM) was used in the interpretation process. In the tidal zone the identification was made by interpreting coastal ortho-photographs from BD Ortho (2005 et 2009) and digitising them on scale 1 : 2000ème with further qualification of the polygons based on ground truth data. For the subtidal zone, several data sources from 2011 were available: bathymetric lidar (with sounding density about 1pt*3m-2), single beam sounder on sonar and video transects, side scan sonar (resolution of about 0.2m), underwater video, grab sediment and fauna samples. In the outer rocky circalittoral zone, side scan sonar corridors were surveyed with a coverage of 30-50% depending on places. In the offshore circalittoral zone (known as La Grande vasière) where soft sediment is predominant, side scan sonar coverage was reduced to about 5-10%. In these latter two circalittoral zones, interpolation between sonar corridors was supported by SHOM « Carte G » (approx. scale 1 : 100 000) along with a 100m resolution depth DTM. On rocky seabed, exposure at the seabed was described using kinetic energy from a combination of wave and current hydrodynamic models according to the methods described in: http://doi.org/10.13155/49975 Rocky substrate in intertidal and infralittoral zones was derived from the combined interpretation of both the topographic and bathymetric Lidar DTMs and aerial photographs, where permitted by water transparency. Various representations of the DTMs (slope, hillshade) helped delineate rocky outcrops with good reliability. Biological qualification of the substrate polygons was made through taxonomic analysis of benthos samples collected by MNHN in the framework of the project « Ecological assessment of Natura 2000 site « Roches de Penmarc’h ».