How many demersal fish species in the deep sea? A test of a method to extrapolate from local to global diversity

Abstract

Grassle and Maciolek (1992) estimated that there were of the order of 107 species of benthic macro-invertebrates in the world's deep sea soft sediments. Their estimate was extrapolated from the 798 species they sampled and the pattern of species diversity observed along a 176km transect on the continental slope of the northeast Atlantic Ocean. Relative to the deep sea invertebrate fauna, the deep sea fish fauna has been better sampled, at least in the upper 1500m. To test the validity of the Grassle and Maciolek method of extrapolation, we applied it to data from a survey of fishes along the continental slope off western Australia, a diverse and previously unsurveyed region. The resulting global estimate for the deep sea demersal fishes – 60000 species – was then compared with the number described to date, about 2650 species, and an estimate of total extant species. Our estimate, which considers the proportion of new species found in little-explored regions of the world ocean, such as off western Australia, and the number of new species expected in future taxonomic revisions, is a total of 3000–4000 species. The Grassle and Maciolek method appears invalid as a means to extrapolate global biodiversity from local surveys.