The Site consists of two small islands (Herm and Jethou), nine rocky islets (including Grande Fauconnière, Crevichon and Brehon Tower), six sandbanks (The Humps) and surrounding shallow tidal waters. The location of Guernsey to the west of the Site creates and supports a diverse range of habitats. The convergence of cold and warm currents and of the corresponding Boreal and Lusitanian biogeographic regions supports an array of species which include rich plankton communities flowing eastward from the Atlantic to the North Sea. The Site has an exceptionally large tidal range – at up to ten metres, it is among the largest in the world – and the intertidal zone is particularly large and biodiverse. Several important habitats are present, including eelgrass (Zostera) beds, maerl beds, shallow reef systems and seven sunken shipwreck reefs, which provide spawning grounds for fish such as sea bass and Black Sea bream, with significant tidal races. The Site is contiguous with benthic habitats supporting flatfish and shellfish, and pelagic habitats supporting seabirds, basking shark, sun fish, Atlantic grey seal and four species of cetacean. The coastlines provide breeding sites for nine species of seabird and Atlantic grey seal. The Site is of economic and cultural importance to the population of Guernsey, and there are significant archaeological and historical features which make it a tourist destination.