Magellan-Antarctic: Ecosystems that drifted apart. Summary Review

While the existence of close biotic relationships between the Magellan region and the Antarctic is beyond doubt, it is clear from the comprehensive review attempted by the IBMANT/97 workshop that there are still some substantial problems to be solved: The fundamental question as to exactly when the two marine ecosystems became separated is not easy to resolve, as can be seen from the variety of suggestions presented by different authors in the literature. The origin of the present day benthic marine faunas both of the Magellan and Antarctic Biogeographic Provinces may date as far back as the Early Cretaceous. However, they remained closely related for some considerable time, and as continents do not drift apart overnight, separation must have been a gradual process which started more than 30 Ma ago and may well have lasted until the late Miocene (some 10-12 Ma ago), when the present conditions were fully established (Crame*). Despite much taxonomic work scattered in the older literature, determination to species level is possible only for a few specialists, many of whom are usually engaged in working up material from other areas. For this reason, we often had to accept preliminary determinations on coarser taxonomic levels despite the referees’ comments that a more ideal piece of work might arise “within a few years time”. Clustering and calculation of diversity would no doubt be strongly improved by breaking all samples down to species level. However, the goal of these proceedings is to define the state of the art, and that is, unfortunately, still very incomplete. From the ecologist’s point of view, we hope this volume may be a challenge to taxonomists, stimulating them to re-investigate those groups where our knowledge is obviously insufficient. Some areas are better studied than others. Although a comparison of the adjacent Magellan and Antarctic Peninsula regions would have been preferable in all cases, some authors have chosen the much better investigated Weddell Sea for comparison. Another source of problems is that the use of geographic subdivisions such as Antarctic, Subantarctic, Antiboreal, Magellan, etc. is inconsistent in the literature, with many authors making their own choice despite the fact that sound bases were created by, for example, Hedgpeth (1969), Deacon (1982) and De Broyer and Jazdzewski (1993, 1996). Even the limits of the Southern Ocean are interpreted in different ways. This significantly hinders the comparison of species richness along the latitudinal gradient (which is difficult anyway, as the inventory SCI. MAR., 63 (Supl. 1): 503-511 SCIENTIA MARINA 1999