Fishes on the Antarctic continental shelf: evolution of a marine species flock?

Distance, currents, deep water and sub-zero temperatures isolate the waters of the Antarctic continental shelf from other shelf areas in the Southern Hemisphere. The Antarctic shelf is an insular evolutionary site for a variety of marine organisms. The fish fauna is relatively small and unusual in composition, consisting of 213 species with higher taxonomic diversity restricted to 18 families. Ninety-six species of perciform notothenioids comprise 45% of the fish fauna. However in many areas of the shelf, including the highest latitudes, notothenioids make up 77% of the species and 90-95% of fish abundance and biomass. Notothenioids are morphologically and ecologically diverse and have diversified into niches in the water column. Antarctic notothenioids were evaluated using criteria employed for assessing freshwater species flocks. Although monophyly is in question. notothenioids exhibit the disproportionate speciosity (5.6-fold more Antarctic than non-Antarctic species) and high endemism (97%) characteristic of a species flock. Notothenioids are one of the first recognized examples of a species flock of marine fishes. Notothenioids are compared with some freshwater species flocks and calculations made of the time required for speciation (TFS) for notothenioids of the family Channichthyidae. Estimates of TFS are slower than for most lacustrine species flocks but similar to estimates for island radiations of birds and arthropods. (C) 2000 The Fisheries Society of the British Isles.