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 varie ty of marine organisms. The fish fauna is relatively small and unusual in c omposition, consisting of 213 species with higher taxonomic diversity restr icted to 18 families. Ninety-six species of perciform notothenioids compris e 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 f ish abundance and biomass. Notothenioids are morphologically and ecological ly diverse and have diversified into niches in the water column. Antarctic notothenioids were evaluated using criteria employed for assessing freshwat er species flocks. Although monophyly is in question. notothenioids exhibit the disproportionate speciosity (5.6-fold more Antarctic than non-Antarcti c species) and high endemism (97%) characteristic of a species flock. Notot henioids are one of the first recognized examples of a species flock of mar ine fishes. Notothenioids are compared with some freshwater species flocks and calculations made of the time required for speciation (TFS) for notothe nioids of the family Channichthyidae. Estimates of TFS are slower than for most lacustrine species flocks but similar to estimates for island radiatio ns of birds and arthropods. (C) 2000 The Fisheries Society of the British I sles.