AN ESTUARINE BIODIVERSITY HOT-SPOT

From 1989-1992, at quarterly intervals, the National Rivers Authority (NRA) (Thames Region) Thames Estuary Benthic Programme sampled 28 site s within the estuary for benthic macroinvertebrates; meiofauna samples were also taken for the first year. At one subtidal site, situated of f Canvey Island, over 200 invertebrate species over the survey period from a sample area of 4.4 m(2) were recorded. This species richness wa s far higher than surrounding sites, including those further out into the North Sea. The most important groups at this site were Nematoda (7 7 spp.), Crustacea (46 spp.) and Polychaeta (40 spp.) and a species ca pture curve for macroinvertebrates continued to rise after 44 day grab s. The mean biomass of the site (248 g wet weight/m(2)) was 20 times t hat of any other site in the outer estuary. The substratum at the site was highly heterogeneous, yet comparatively stable due to its situati on at the base (>20 m depth) of a man-made shipping channel, the provi sion of a large number of niches perhaps explaining the high biodivers ity. The anthropogenic influence on a naturally low biodiversity area emphasises the importance of these ecosystems when considering the con servation of global biodiversity. Methods to determine the relative im portance of ecosystems are discussed.