Antarctic marine benthic biodiversity in a world-wide latitudinal context

In the 1950s and 1960s, the first data sets were assembled to examine wheth er or not there was a latitudinal gradient of species richness in the sea. These data comprised very few species and were from very small areas. Howev er, recent data from large species lists covering broad geographical ranges suggest strongly that there is a gradient of increasing species richness f rom the Arctic to the tropics. However, the Southern Ocean has high species richness and in the southern hemisphere there is no clear evidence of a cl ine of increasing richness from pole to tropic. The great richness of the S outhern Ocean compared with the Arctic is probably due to its great age, th e fact that it covers a much larger area and that it has higher structural heterogeneity formed by living organisms. The importance of area as a deter minant of species richness needs to be studied in more detail since most st udies have been confined to small areas. A number of hypotheses have been p roposed to explain the species:area relationship and these are discussed. A n alternative explanation for the latitudinal cline in the northern hemisph ere is the energy-input hypothesis. but again this has not been adequately tested. Two studies on the relationship between local and regional species richness show a significant positive correlation. These findings suggest th at local assemblages are not tightly organised and saturated with species b ut are open to recruitment from the regional species pool. Whether or not s uch a relationship holds in Antarctica is unknown. It is concluded that fur ther studies of the Southern Ocean are likely to provide new findings funda mental to the "new" discipline of macroecology, which examines patterns and processes at the geographic scale.