Probing the depths

W scientists from HMS Challenger dredged animals from over 5km depth, they finally laid to rest the azoic hypothesis of Edward Forbes, that life could not exist in cold dark depths of the ocean, and thereby opened the doors to true deep-sea biology. The past decade has witnessed a further sea change in our view of marine diversity, if I may be permitted the pun, a change driven to a large extent by improved knowledge from Antarctica. For many years we viewed the tropics as the engines of diversity; species arose in warm clear seas, especially those associated with coral reefs, and spread slowly to populate the harsher high latitudes. Early studies of the isopod fauna had also suggested that at least some organisms living on the continental shelf of Antarctica may have originated in the deep sea. After a period of intense work, much of it under the auspices of the SCAR EASIZ (Ecology of the Antarctic Sea Ice Zone) and more recently the EVOLANTA (Evolution in Antarctica) programmes, we can now modify both hypotheses, with powerful implications for our understanding of global marine diversity. The marine invertebrate fauna of the Antarctic continental shelf is now better described than might be thought, and the total fauna may well exceed 17000 taxa. Interestingly, there are very few places in the world with comparable data, but we can say that the fauna has had a long history of evolution in situ and is not simply a last refuge for taxa that originated elsewhere Basic systematic work may be unpopular with funding agencies, but without it we cannot make the broad generalisations needed by the community and demanded by politicians. Such work is particularly important in the deep sea, and it is in the deep waters around Antarctica that we are currently witnessing our most rapid growth of knowledge of marine diversity, primarily as a result of the ANDEEP cruises. The original idea that deep sea organisms are preadapted to Antarctic conditions has been upset by the recognition that conditions in the deep sea are largely dictated by high latitude oceanography. But the combination of traditional systematics with modern molecular techniques is indicating that some taxa have moved down from the shelf into deep water, as well as others moving the other way. Work from Antarctica is rewriting our view of the relationship between the faunas of the deep sea and the continental shelf. One of the most important insights has been the recognition that many groups of organisms have radiated in Antarctica. The classic case is the notothenioid fish, so well recognised now that they are now a textbook example. Here the radiation was identified by traditional systematics techniques, but molecular tools have provided important support, in some cases changing the details, and allowed us to date the radiation, albeit imprecisely as yet. Similar techniques have identified other important radiations, including lipariid fish in deeper water, amphipods, isopods, pycnogonids and some groups of predatory gastropods. We would like to be able to date these radiations from fossils, but here we are impeded by the relative paucity of suitable exposures, particularly at climatically important times in the Cenozoic. We do, however, have a rapidly developing picture of the tectonic context and associated climatic changes. This makes Antarctica a unique laboratory for setting evolutionary changes in their environmental context. The papers in this issue demonstrate that evolutionary studies are alive and well in Antarctic science. Work in the deep waters may be expensive and time-consuming, but without plumbing these depths we will miss vital clues to our global understanding of how life on earth evolved. Yet again Antarctica, remote but highly relevant, is providing key insights into fundamental processes. ANDREW CLARKE DOI: 10.1017/S0954102004001737