Southern Ocean Marine Research Articles

The origin of the Southern Ocean marine fauna

Abstract Current knowledge of the break-up of Gondwana during the Tertiary indicates that shallow water marine habitats may have been present continuously, and on occasions were considerably more extensive than at present. Although direct fossil evidence is sparse after the Eocene, geophysical evidence suggests that shallow waters have been present since the late Mesozoic, and possibly much longer. The break-up of Gondwana was accompanied by a more or less steady lowering of both surface and bottom temperatures in the Southern Ocean from about 15°C in the Late Cretaceous to the present range of roughly +2 to −1.8°C. Microfossils in deep-sea drilling cores indicate that temperature drops were particularly sharp in the early Oligocene ( c. 38 Ma), mid-Miocene (10–14 Ma) and Pliocene ( c. 4 Ma BP). Geological evidence suggests that the Drake Passage opened, and the present oceanographic regime established, about 25–30 Ma BP. This is now known to be about the time of full-scale development of the East Antarctic ice cap. Subsequently ice sheets extended across, and deeply eroded, the continental shelves but the effects of these glacial maxima on the marine biota are not fully understood. Late Cretaceous/early Tertiary marine fossils from the James Ross Island group indicate a diverse shallow water marine fauna, including two groups notably lacking in diversity in the living fauna: decapods and teleost fish. In several genera occurrences in this fauna predate first occurrences in lower latitudes by as much as 40 Ma, suggesting the possibility that a number of groups originated at high southern latitudes. The living fauna exhibits a high biomass in many areas, and within-site diversity can be as high as anywhere in the world. Some individual taxonomic groups, however, (notably bivalves and gastropods) have a lower diversity than in the tropics, supporting the concept of a latitudinal cline in diversity. Studies of physiological adaptation to temperature suggest that the decline in seawater temperature during the Cenozoic has not presented a particularly severe evolutionary problem. The reasons for the absence of large decapods and the low diversity of fish in the present fauna are unclear. Most of the biological features of the modern fauna are more likely a response to the seasonality of the ecosystem rather than low temperature per se . Overall the evidence suggests that the present Southern Ocean shallow water marine fauna largely evolved in situ, having been present since at least the Late Cretaceous, and possibly much longer. Some groups have invaded, for example along the Scotia arc, but the isolation of the Southern Ocean by the present oceanographic regime and the limited dispersal ability of many forms means that exchange with lower latitudes is very slow.

Science to Support the Management of Southern Ocean Marine Living Resources

AbstractThis paper is a slightly edited version of chapter 2 of the Report on Australia’s Antarctic Science Program prepared by the Antarctic Science Advisory Committee for the Minister for Arts, Sport, the Environment, Tourism and Territories.

The Calanoid Copepod Euchaeta Antarctica from Southern Ocean Atlantic Sector Midwater Trawls, with Observations on Spermatophore Dimorphism

Stage V amd VI copepodids of the predatory calanoid copepod Euchaeta antarctica were counted from Southern Ocean Atlantic Sector trawl samples collected during 9 months over a 5-year period. The proportion of CVI males to all CVI animals reached a maximum in June; the proportion of CVI males to total males reached a maximum in July. Two morphologically distinct kinds of spermatophores were attached to 2 different areas on the genital segment of females, and were correlated with 2 kinds of spermatophores held in leg 5 and contained within the bursa of different males. Possible adaptive significance ofspermatophore dimorphism and placement for Euchaetidae is discussed and further studies are outlined. From 1962 to 1972, the National Science Foundation's United States Antarctic Research Program (USARP) supported surveys of Southern Ocean marine organisms. Collections included over 1,000 3-m Isaacs-Kidd midwater trawl samples of the pelagic midwater fauna. In the Atlantic Sector, samples were taken during most months of the year. Samples were collected initially by the research staff of the University of Southern California and later by scientists from the Smithsonian Oceanographic Sorting Center, Woods Hole Oceanographic Institution, and Texas AM Wolfenden, 1908, 1911; Farran, 1929; Vervoort, 1951, 1957, 1965; Yamanaka, 1976; Park, 1978). Records north of the Antarctic Convergence by Yamanaka (1976) and Park (1978) off Argentina, and Vervoort (1957) in the Indian Ocean generally are from greater depths. Recently specimens have been collected from as shallow as 10 m off Isla Madre de Dios in the Chilean fjord system (Marin and Antezana, 1985). The vertical distribution limits of E. antarctica have yet to be studied systematically through 1 year, although Hopkins'(1985a) collected it to 1,000 m (his deepest samples) in March and April; Yamanaka (1976) reported specimens to 4,000 m in July, August, October, and December. Its presence in plankton samples taken under ice has been noted in the Ross Sea by Farran (1929) at Cape Evans, Ross Island, and by Bradford (1981) at McMurdo Sound. Littlepage (1964) studied seasonal changes in lipid content of adults from McMurdo Sound. Reports of biological interactions include an outline of its trophic position in the pelagic community during March and April (Hopkins, 1985b) (it fed on pelagic copepods, e.g., Oncaea and Metridia, and was eaten by a fish, Electrona antarctica), and its predation by a benthic brittle star, Astrotoma agassizii (Dearborn et al., 1986).

The food and feeding ecology of Adélie penguins (Pygoscelis adeliae) and Chinstrap penguins (P. antarctica) at Signy Island, South Orkney Islands

Adélie Pygoscelis adeliae and Chinstrap P. antarctica penguins are important consumers of Southern Ocean marine resources. The stomach contents of adult penguins at Signy Island, South Orkney Islands, were analysed quantitatively throughout the chick‐rearing period. They consisted almost exclusively of Antarctic krill Euphausia superba, Adélies eating 35–63% by number and 23–28% by weight of juvenile krill and Chinstraps 72–87% by number and 90–95% by weight of mature krill, as well as small amounts offish and amphipods. Interspecific dietary differences may partly be attributable to Adélies starting breeding one month before Chinstraps but, as they persist when both are simultaneously rearing chicks, the two species may also forage in somewhat different areas.Krill data from net hauls indicate a substantial overlap in the size of krill taken by scientific, and probably also commercial, operations and by Adélie and Chinstrap penguins.Chicks were fed c. 300 g of food 0–5‐0‐8 times per day, Chinstrap chicks without a sibling being fed most frequently. Chicks of both species were most often fed in the late afternoon, and from estimates of swimming speed and feeding frequency adults may feed quite extensively at night.