An estuarine biodiversity hot-spot

From 1989-1992, at quarterly intervals, the National Rivers Authority (NRA) (Thames Region) Thames Estuary Benthic Programme sampled 28 sites within the estuary for benthic macroinvertebrates; meiofauna samples were also taken for the first year. At one subtidal site, situated off Canvey Island, over 200 invertebrate species over the survey period from a sample area of 4.4 m(2) were recorded. This species richness was far higher than surrounding sites, including those further out into the North Sea. The most important groups at this site were Nematoda (77 spp.), Crustacea (46 spp.) and Polychaeta (40 spp.) and a species capture curve for macroinvertebrates continued to rise after 44 day grabs. The mean biomass of the site (248 g wet weight/m(2)) was 20 times that of any other site in the outer estuary. The substratum at the site was highly heterogeneous, yet comparatively stable due to its situation at the base (>20 m depth) of a man-made shipping channel, the provision of a large number of niches perhaps explaining the high biodiversity. The anthropogenic influence on a naturally low biodiversity area emphasises the importance of these ecosystems when considering the conservation of global biodiversity. Methods to determine the relative importance of ecosystems are discussed.