Publication Abstract

Mapping Rocky Reefs in the Central English Channel: a case study using nested surveys and broadscale acoustic proxies

R. Coggan*, M. Diesing*, K. Vanstaen*

The EU Habitats Directive requires member nations to protect a representative proportion of certain marine habitats that occur within their waters. Rocky reefs are one of seven habitats listed for special consideration, but in UK waters they are not well mapped. Without knowing the location and extent of rock outcropping at the seabed surface, it is difficult to establish what constitutes a ‘representative proportion’ of the UK’s rocky reefs.

This paper reports on a search for rocky reefs in the central English Channel. We surveyed two areas where rock was indicated on seabed sediment charts. In one area we found hardly any rock at the seabed surface. In the other we found outcrops over a far more extensive area than expected. The reefs were characterised using a combination of acoustic surveys (multibeam and sidescan sonar) and underwater video and photography. Large sponges were a feature at sites > 50 m depth.

Digital Survey Bathymetry (SeaZone Solutions Ltd.) of the central English Channel provides a fascinating insight into the complex topography of the area (Figure 1). Drawn mainly from single-beam acoustic surveys, it places our multibeam surveys and geological knowledge in a wider spatial context and allows us to delineate a reef area in the order of 1,000 sq km (about twice the size of the Isle of Wight).

Our study demonstrates the considerable potential benefits that existing broadscale topographic data can bring to seabed mapping at the regional scale, by using seabed character as a proxy for habitats identified during site-specific surveys. The resolution and extent of the resulting maps are well aligned with the information needs of regional management and implementing policy objectives of the Habitats Directive.

Reference

R. Coggan*, M. Diesing*, K. Vanstaen* (2008) Mapping Rocky Reefs in the Central English Channel: a case study using nested surveys and broadscale acoustic proxies. GeoHab Conference, Alaska, May 2008