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The ship was stopped to take soundings and to dredge, and a good haul was brought up from the bottom of the most beautiful things imaginable. The bottom of this sea must be covered with the most wonderful collection of starfish, sea urchins, Polyzoa, crustaceans, etc. All fairy-like delicate things that reminded one much more of the Tropics but all living at a temperature of 29°F.
Edward Wilson, Diary of the Discovery Expedition
Antarctica is a good place to study both evolution and adaptation. Despite the low temperatures and lack of liquid water on land, and the effects of sea ice and temperatures just above freezing in the sea, Antarctic organisms have found ways not only to survive but to thrive in what to us seem very difficult environmental conditions. Its unusual evolutionary history, from Gondwana supercontinent to the present day, together with a climate that has now been cold for at least 25 million years, gives Antarctic biodiversity some unique features, whilst the survival techniques that its plants, animals and microbes have developed can provide important insights into the physiological and biochemical ways in which organisms function. It is on land that physical environmental extremes are perhaps most obvious, and the continent's terrestrial habitats include some of the coldest, driest, windiest and most abrasive to be found anywhere on Earth. Less than 0.4% of the Antarctic is ever free of ice or snow cover, and even then this may be for as little as a few days or weeks during the height of the summer. In this respect Antarctica is strikingly different to the Arctic. The latter experiences a similar radiation (daylength) regime, determined by latitude, which means that both polar regions face similar thermal stresses during their winter months when the input of solar energy is absent. In summer, the almost complete ice cover of Antarctica gives it a very high albedo, reflecting virtually all incoming solar radiation back up through the atmosphere. In contrast, large areas of the northern continents and archipelagos, and, increasingly, the surface of the Arctic Ocean, become ice free for several months during summer, enabling the absorption of solar radiation and leading to temperatures several degrees higher on average than at comparable Antarctic latitudes, sufficient to support considerable biological productivity.
During the Joint Chilean–German–Italian Magellan ‘Victor Hensen’ Campaign in 1994 an epibenthic sledge (EBS) was used to catch the epibenthic and benthic-boundary-layer macrofauna.
Eighteen EBS samples were taken at 12 locations on a transect through the Beagle Channel. The aims of the study were to describe the epibenthic molluscan species, to quantify their abundances and to describe their distribution. In total 35,087 specimens were collected, yielding 107,223 ind 1000 nr−2. Bivalvia were most abundant 78,615 individuals (52 spp.) followed by Gastropoda (17,289, 52spp.), Aplacophora (4745, 9 spp.), Polyplacophora (4665) and Scaphopoda (1909,5 spp.). The molluscan abundance of the hauls were strikingly different, between 3 and 37,927 ind 1000 m−2 haul. Only stations off the eastern entrance showed high abundances, which was represented at all depths and sediments. Elsewhere the abundances were low. Species richness was highest in shallow water (< 100 m) with 69 species and decreased with depth. But at the deepest station 37 species were found.
The remote South Sandwich arc is an archipelago of small volcanic islands and seamounts entirely surrounded by deep water and about 600 km away from the closest island, South Georgia. As some of the youngest islands (< 5 m.y.) in the Southern Ocean they are ideal for studying colonization processes of the seabed by benthic fauna, but are rarely investigated because of remoteness and extreme weather. The current study attempted to quantify the richness and abundance of the epibenthic macrofauna around the Southern Thule group by taking five epibenthic sledge samples along a depth transect including three shelf (one at 300 m and two at 500 m) and two slope stations (1000 and 1500 m). Our aim was to investigate higher taxon richness and community composition in an isolated Antarctic locality, since recent volcanic eruptions between 1964 and 1997. We examined patterns across all epibenthic macrofauna at phylum and class levels, and investigated trends in some model groups of crustaceans to order and family level. We found that abundance was highest in the shallowest sample and decreased with depth. Shelf samples (300 and 500 m) were dominated by molluscs and malacostracans while at the deeper stations (1000 and 1500 m) nematodes were the most abundant taxon. Surprisingly, the shallow shelf was dominated by animals with restricted dispersal abilities, such as direct developing brooders (malacostracans) or those with lecithotrophic larvae (bivalves of the genus Yoldiella, most bryozoan species). Despite Southern Thule's geological youth, recent eruptions, and its remoteness the shallow shelf was rich in higher taxa (phyla/classes) as well as orders and families of our model groups. Future work at higher taxonomic resolution (species level) should greatly increase understanding of how life has reached and established on these young and highly disturbed seabeds.
Present day Southern Ocean benthic biodiversity is the result of climatic changes based on the break-up of Gondwana in the Cretaceous and the Cenozoic and the physiological potential of the fauna to cope with the climatic deterioration. Though many taxa survived the thermal drop in ocean bottom temperatures, zoogeographic ranges changed and some faunal elements even became extinct, e.g. benthic decapods and teleost fish, opening up new ecological niches and the potential for enormous adaptive radiations within some taxa, like the amphipods and isopods (peracarid crustaceans) and notothenioid fish. Ice-sheet extensions and retreats might have enhanced speciation processes as well as eurybathy. Biodiversity on the Antarctic shelf is high within the polychaetes, molluscs, and echinoderms, and within the amphipods and isopods possibly due to the Cenozoic extinction of the benthic decapods. Moreover, some shelf areas are characterized by accumulations of large suspension feeders like poriferans, bryozoans, ascidians, gorgonians, and hydroids. Palaeoclimatic changes also caused that many taxa of the modern, present day Southern Ocean benthic organisms are characterized by gigantism, slow metabolism, longevity, and a reduced number of offspring combined with late maturation. However, our biological knowledge is mainly confined to Southern Ocean shelf organism; we do not know much about the composition, biodiversity and zoogeography of the Southern Ocean deep sea animals. On this background the deep sea expeditions ANDEEP were born and the background and first results of these are presented herein.
Detailed redescriptions of the poorly known isopods Cymodocella tubicauda Pfeffer 1887 and Exosphaeroma gigas (Leach 1818) are presented in order to allow easier identification of these two species. Similarities to and differences from other species of the genus are discussed.
An inventory of Antarctic and Subantarctic mysid fauna is presented, together with a summary of the present state of knowledge of species and their taxonomic diversity, geographic and bathymetric distribution patterns. Fifty nine species of Mysidacea (Crustacea, Peracarida) are now known. Of these, 37 were reported for the Antarctic region and 31 for the Magellan region; six species occur further north in the Southern Ocean, but south of 40°S. 51% of the Antarctic Mysidacea are endemic, and the figure for the Magellan region is 48%. Most of the species live hyperbenthically, but some also occur bathy- or mesopelagically. Mysidetes has the most species in the Southern Ocean, and Eucopia australis is the species with the widest bathymetric distribution (600–6000 m depth). It is concluded that an emergence of species onto the Antarctic shelf in the Neogene was quite unlikely, because none of the mysid species is a true deepsea species, and most species occur on the shelf or at the shelf break. It is more probable that present day species colonized the Southern Ocean via shallower waters. The examples of the distribution of different genera suggest that the Mysidacea of the Southern Ocean probably had various geographical origins.
Two specimens of Dolichiscus spinosetosus were collected by means of an Agassiz trawl and a small dredge in the Weddell Sea, Antarctica. This species is characterized by a large number of strong spines on the dorsal side, some of these possessing tubercular tips. The dorsum is characterized by many smaller and shorter blunt spines and numerous long simple setae all over the body (on spines, pereonites and pleotelson). Dolichiscus acanthaspidus Schultz, 1981 is the taxon most closely related to this new species, but the new species has more setae and tubercular spines on all parts of the body and two caudolateral spines instead of one behind the supraocular ones.
In November 1994 epibenthic sledge samples were taken in the Beagle Channel. This study presents the first systematic account of Tanaidacea of the Beagle Channel and an adjacent area on the Atlantic continental slope. The material of this part from the Magellan Strait comprised 2175 specimens and 27 species of eight families of Tanaidomorpha and two families of Apseudomorpha. Eleven species were sampled in the Magellan region for the first time. The genus Stenotanais (Anarthruridae) was reported for the first time in the Southern Hemisphere and, the bathymetric range of seven species was extended. The tanaidacean fauna in the Beagle Channel is highly heterogeneous with 36 tanaidacean species now known from the Magellan region. On the basis of a zoogeographic comparison of the Magellan region with sub-Antarctica and Antarctica, Sieg's (1988) hypothesis of a phylogenetically young, derived Antarctic tanaidacean fauna is examined and the zoogeographic relationship between the Magellanic Tanaidacea and the Antarctic tanaidaceans is discussed.
Composition, abundance, and distribution of suprabenthos from a depth between 1 and 1.33 m above the seafloor were analysed. The samples were taken during ANT XV/3 with RV Polarstern in February and March 1998 by means of the supranet of an epibenthic sledge along two transects in the southern Weddell Sea (Vestkapp and Halley Bay) and one east of King George Island. At each of these three transects, five to six stations were taken in water depth between 200 and 2000 m. In total, 34 057 specimens were sampled at 16 stations, yielding 1 205 050 individuals for all stations standardized to 1000 m3 hauls. Of these, copepods were usually the most abundant group in the supranet (805 822 ind 1000 m−3. The suprabenthic fauna of the southwest of Vestkapp (Weddell Sea) transect was dominated by planktonic taxa in terms of individual numbers especially at the deeper stations (938–1983 m). At Halley Bay the total abundance of plankton was lower but its relative abundance (> 80%) was also high, whilst off King George Island peracarid crustaceans were an important fraction.
Abundance, diversity, and distribution of suprabenthic Isopoda caught from a water layer between 0.27 to 0.60 m above the seafloor were analysed. The samples were taken during the ANT XV/3 cruise on RV Polarstern by means of an epibenthic sledge along two transects in the southern Weddell Sea (Vestkapp and Halley Bay) and another one east of King George Island. At each of these three bathymetric transects, five to six stations were sampled between 200 and 2000 m. In total, 4258 specimens of isopods were sampled at 14 stations standardized to 1000 m2 hauls. 114 species were identified from 49 genera and 23 higher taxa (families and suborders) of Isopoda. Most of them belonged to the suborder Asellota. Dominant families are Munnopsididae (Eurycopinae, Ilyarachninae), Joeropsidae, Munnidae, Paramunnidae, Ischnomesidae and Desmosomatidae. No striking differences were found between areas (Vestkapp, Halley Bay, Kapp Norvegia, and Bransfield Strait). Overall isopod abundances were highest at the shallowest station; species richness was slightly higher above 1000 m depth.
Amphipoda belong to the most abundant benthic organisms of Antarctica, the Epimeriidae being one of the most dominant families. Morphological characters are used to explore relationships between the species of all Antarctic Epimeria, the genus representing 70% of Antarctic epimeriid species. Additional Epimeria from the deep sea off Brazil, the Tasman Sea and from shallow Norwegian waters are analysed. Species of Epimeriella and Metepimeria, as well as iphimedoid taxa are also considered. High intraspecific variation was observed, which was not related to size, sex, or locality and may indicate recent speciation of some Antarctic epimeriids. The small number of taxa studied from the deep sea and the northern hemisphere and difficulty in defining apomorphic and plesiomorphic states does not allow us to present final conclusions about the origin of Antarctic Epimeria living on the Antarctic shelf. Nonetheless, deep-sea species from the mid-Atlantic form a clade with deep-sea species from the western Pacific and two of the three studied North Atlantic species. This supports the Watling & Thurston (1989) hypothesis that Antarctica acts as an evolutionary incubator.
The composition of suprabenthic Peracarida from a depth between 1 and 1.33 m above the seafloor was investigated. In order to study the abundance and diversity quantitatively, the samples were taken by means of the supranet of an epibenthic sledge off Kapp Norvegia and off the South Shetland Islands. The samples were taken during ANT XVII-3 with RV Polarstern in April and May 2000. These samples of EASIZ III received during the Antarctic autumn are compared with those of EASIZ II taken during the summer. While the autumn samples show far less abundance of all peracarid taxa, the diversity is about twice as high as during summer. In total 115 species of peracarid crustaceans were sampled at six stations yielding 1336 individuals standardized to 1000 m3 hauls. Amphipoda clearly dominated in abundance and diversity.
Apseudes heroae Sieg, 1986 (Family Apseudidae) and Allotanais hirsutus (Beddard, 1886)
(Family Tanaidae) are common Tanaidacea of the southern Magellanic region. The aim of the investigation
is to elucidate the postmarsupial development of these tanaid species that differ in their biogeography.
Population structures are analysed from size frequency data and from different postembryonic stages of
specimens collected in the Atlantic entrance of the Beagle Channel and from the Atlantic continental slope
to the south-east. The population of Apseudes heroae shows three age groups, the one of Allotanais hirsutus
probably at least three. Some large specimens indicate that the latter sub-Antarctic species might reach an
age of several years. Both species are probably gonochoristic, and protandric hermaphroditism was not
observed. The fecundity of Apseudes heroae and Allotanais hirsutus was analysed. No significant
correlation could be found between cephalothorax width and egg number or number of larvae. For both
species hypothetical life cycles are reconstructed. As sub-Antarctic temperatures are low and seasonality is
strong in the Magellanic region, it is possible that these species are reasonably adapted in reproduction as
shown in some polar species of Isopoda and Cumacea.
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