Description and ecology of a new species ofEdwardsiade Quatrefages, 1842 (Anthozoa, Actiniaria) from the St Lucia Estuary, South Africa

A new species of the true anemone genus Edwardsia, E. isimangaliso sp. nov., is described from the St Lucia Estuary, Africa's largest estuarine lake. The species differs from its closest relatives in anatomy and cnidom and is the only species of the genus found in hypersaline waters. Its current distribution appears to be restricted to a narrow region in the middle reaches of the estuary (lower South Lake), where it has been recorded at salinity levels ranging from 21 to 55.6 psu. The species is also limited to substrata dominated by fine to very fine sand and does not occur in areas with either high silt or coarse sand content. Population densities appear to have decreased over time, with maxima over 1500 ind. m−2 recorded in 2005, but only 20 ind. m−2 in 2010. Prey items identified in its stomach include the snail Assiminea ovata and ostracods. However, stable isotope analysis showed that the main carbon sources for the anemone are the filamentous macroalga Cladophora sp. and benthic microalgae. The presence of zooxanthellae in tissues of E. isimangaliso sp. nov. suggests that the species may combine heterotrophic and autotrophic feeding modes in response to fluctuations in resource availability.