Abstract

The latitudinal cline in diversity is a well established, though poorly understood, feature of terrestrial communities and although it is often assumed that a similar cline is to be found in the sea, the evidence for this is still equivocal. Attempts to develop an overall picture of diversity in the sea are made difficult by the small number of key studies, the varied sampling protocols employed in these studies, the different measures of diversity utilised and the varying levels of taxonomic resolution. Nevertheless, there is clear evidence for greater species richness in the tropics for several shallow-water taxa that depend on calcareous skeletons, including gastropod and bivalve molluscs, foraminifera and hermatypic corals. There is also an increasing body of evidence for a latitudinal diversity cline in the deep sea, at least in the northern hemisphere. However, any cline in species richness in the northern hemisphere will, in part, be a necessary consequence of the depauperate Arctic fauna and the intense species richness of the Indo-West Pacific. The Southern Ocean is now known to support a rich and diverse shallow-water benthic fauna, the striking contrast to the Arctic being the result of a very different tectonic and evolutionary history. Whereas the Arctic marine system is very young and still being colonised, the Southern Ocean marine fauna has essentially evolved in situ, and has been influenced by a dynamic glacial and climatic history.