Shallow-water benthic hydroids from Tethys Bay (Terra Nova Bay, Ross Sea, Antarctica)

The shallow-water hydrozoan Antarctic fauna is still poorly studied, and available knowledge mostly refers to samples gathered by traditional ship-operated gears. By scuba diving in the coastal areas off the Italian Antarctic station “Mario Zucchelli” (Ross Sea, Terra Nova Bay), in the austral summer 2002–2003, a total of 20 hydrozoan species were found, belonging to 10 families and 13 genera. As hypothesized, Anthoathecata (11 species), usually under-represented in collections from indirect sampling gears, are common as also are Leptothecata (9 species). Hydractiniidae and Hydractinia are the dominant family and genus, followed by Haleciidae and Halecium. A new species to science, Halecium exaggeratum sp. nov. is also described. Most species are either endemic to Antarctic waters or restricted to Antarctic/sub-Antarctic areas; only two species have a wider distribution. Material reared in aquaria at the Italian Antarctic Base Mario Zucchelli facilitated knowledge of the life cycle and reproductive biology of several species. In particular, Opercularella belgicae was found to liberate a medusa stage referable to Phialella, and the species is assigned here to that genus, as Phialella belgicae. Also, extraordinary is the complete absence or scant representation of the most typical Antarctic benthic hydroid genera (Antarctoscyphus, Oswaldella, Schizotricha, Staurotheca, and Symplectoscyphus), likely related to the shallow limits of sampling (down to 48 m).     

Picoplankton BIOMASS in the Ross Sea (Antarctica)

Summary Spatial distribution of picoplankton in the Ross Sea was studied. The authors discuss the biomasses of various picoplanktonic-sized fractions and of bacterial cells between 0.2 and 2.0 m capable of growing on Marine Agar 2216 (Difco). Picoplankton having a cellular diameter cf between 1.0 and 2.0 m (PP1) generally predominate, accounting for 73% of the whole picoplankton biomass. However, smaller cells (PP2) can represent 28% of the picoplankton biomass at depths corresponding to 1% of surface light. These results are in good agreement with those found in the coastal regions of McMurdo Sound (Fuhrman and Azam 1980) and in other areas of the Antarctic seas where total bacterioplankton was studied (Hanson et al. 1983b; El-Sayed 1987; Lancelot et al. 1989). Biomasses of total picoplankton (TPP) are not correlated with any of the environmental parameters studied. The PP1 is correlated with O₂ and silicates and PP2 is correlated with O₂, phosphates temperature and nitrates. Aerobic heterotrophic biomasses are correlated with O₂ and salinity.     

Composition, abundance and stratification of soft-bottom macrobenthos from selected areas of the Ross Sea shelf (Antarctica)

Composition, abundance and stratification of soft-bottom macrobenthos were studied at three selected sites on the Ross Sea shelf (Antarctica) with different geomorphology and sedimentation regimes. Sites A (southwest Ross Sea, 810 m depth) and B (Joides basin, 580 m depth) were characterized by biogenic mud and clay sediments, whereas site C (Mawson bank, 450 m depth) featured sandy sediments mixed with a conspicuous biogenic component characterized by shells and tests of calcareous invertebrates (mainly barnacles of the genus Bathylasma). The macrofauna of sites A and B was mainly composed of infaunal polychaetes and bivalves. The assemblages comprised both surface and sub-surface deposit feeders, including some conveyor-belt polychaetes (Maldanidae and Capitellidae) that are responsible for high sediment mixing and bioturbation. The macrobenthos of site C was dominated by crustaceans, polychaetes and echinoderms (ophiuroids), and mainly by filter feeders and epifaunal or interstitial forms. Abundances were higher (up to 1040 ind. m⁻²) at site B than at sites A and C (430 and 516 ind. m⁻², respectively). At sites A and B the benthos was mainly concentrated in the upper 5 cm of the sediment, and abundances declined sharply in the deeper sediment layers. These results indicate a high degree of consistency between sediment features and benthic community structure, which are both strongly related to local hydrography and bottom dynamics. Sites A and B represent areas where the organic input to the seafloor by vertical sedimentation from the upper water column is high. Site C, however, is characterized by high sediment instability and food particles advecting mainly horizontally. The community is more physically controlled by unpredictable, and probably frequent, disturbance events (e.g., bottom turbid currents, sediment reworking and displacement). Individuals were relatively small, indicating that probably they are not able to grow up to the adult size and reproduce. The community may be represented by “pseudopopulations” depending on the settlement of larvae invading from neighbouring areas. Accepted: 23 October 1998     

Macrofaunal communities on the continental shelf and slope of the southeastern Weddell Sea,Antarctica

Summary During the third leg of the European Polarstern Study (EPOS leg 3) in the austral summer season 1989, benthic macrofaunal communities were sampled from the Elephant Island area (61° southern latitude) and from Kapp Norvegia (71° southern latitude) to Halley Bay (75°30 southern latitude) using a commercial bottom trawl and an Agassiz trawl. Thirty-six trawl samples from a depth range of about 200–2,000 m were considered, with most of the samples being from the shelf and upper slope. Multivariate analysis techniques (clustering and TWIN-SPAN) discriminated between an eastern and a southern community in which parallel subgroups can be distinguished at increasing distance from the ice shelf.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Potential impact of the main benthic amphipods on the eastern Weddell Sea shelf ecosystem (Antarctica)

As they represent one of the most diversified taxonomic groups on Antarctic bottoms, amphipods are likely to play a complex role in biogeochemical fluxes that occur within benthic ecosystems. The aim of this paper is to present, using both digestive tract analyses and relative species abundance data, the impact of amphipod feeding on different potential preys of the Weddell Sea. The study is based on data obtained for 29 representative amphipod species collected at 130 stations distributed along the eastern shelf of the Weddell Sea (depth range: 60-2,000 m) during three summer cruises, from 1989 to 1998. Sedimenting plankton particles (10-27%), crustaceans (22-32%) and fish carrion (5-18%) are the main food resources. Other abundant potential preys, such as molluscs or tunicates, do not seem to be consumed. Variations in the proportions of the different preyed food items are observed, mainly related to differences in relative amphipod species composition in samples. Presented results will help in refining ecological models of the prospected area, but also underline the need for accurate and reliable measurements of the feeding rates of Antarctic benthic organisms.     

Filling biodiversity gaps: benthic hydroids from the Bellingshausen Sea (Antarctica)

The Bellingshausen Sea constitutes the third largest sea in the Southern Ocean, though it is widely recognized as one of the less-studied Antarctic areas. To reduce this lack of knowledge, a survey to study the biodiversity of its marine benthic communities was carried out during the Bentart 2003 and Bentart 2006 Spanish Antarctic expeditions. The study of the hydroid collection has provided 27 species, belonging to ten families and 15 genera. Twenty-one out of the 27 species constitute new records for the Bellingshausen Sea, raising the total number of known species to 37, as also do nine out of the 15 genera. Candelabrum penola, Lafoea annulata, and Staurotheca juncea are recorded for the second time. Most species belong to Leptothecata. Sertulariidae with 13 species (48%) is by far the most speciose family, and Symplectoscyphus with seven species (26%), including S. bellingshauseni sp. nov. and S. hesperides sp. nov., the most diverse genus. Considering the whole benthic hydroid fauna of the Bellingshausen Sea, 18 species (69%) are endemic to Antarctic waters, either with a circum-Antarctic (12 species, 46%) or West Antarctic (6 species, 23%) distribution, 23 (88%) are restricted to Antarctic or Antarctic/sub-Antarctic waters, and only three species have a wider distribution. Bellingshausen Sea hydroid fauna is composed of a relatively high diversity of typical representatives of the Antarctic benthic hydroid fauna, though with a surprisingly low representation of some of the most diverse and widespread Antarctic genera (Oswaldella and Schizotricha), what could be related to the fact that its shelf-inhabiting hydroid fauna remains practically unknown.     

Elemental composition, total lipid content, and lipid class proportions in zooplankton from the benthic boundary layer of the Beaufort Sea shelf (Canadian Arctic)

Biochemical analyses such as lipid class and elemental composition can inform us about a species’ role in community energetics and nutrient cycling. The accumulation of lipid-rich energy stores affects the elemental composition and stoichiometry of animal tissues, and this relationship is especially relevant to zooplankton at higher latitudes due to increased seasonal lipid storage. However, due to sampling difficulties, the elemental composition and energy storage capabilities of polar, benthic boundary layer zooplankton are poorly known. We determined elemental and lipid class compositions for 26 taxa of benthic boundary layer zooplankton from the Beaufort Sea shelf. Elemental composition as a percentage of dry weight ranged 21–56% for carbon (C), 4–11% for nitrogen (N), and 0.1–1.1% for phosphorus (P) across all taxa. C concentration and C:N were positively correlated with the storage lipids triacylglycerols (TG) and wax esters/steryl esters (WE/SE) and negatively correlated with membrane lipids (phospholipids and sterols). Most taxa had high levels of storage lipids, generally TG. High levels of WE/SE were found in the copepod Calanus hyperboreus (>90% of total lipid) and the chaetognath Eukrohnia hamata (72%). In contrast, the chaetognath Parasagitta elegans had only minor proportions of both TG and WE/SE. The high levels of storage lipids in most taxa indicate that feeding behavior of benthic boundary layer zooplankton on the Beaufort Sea shelf is tightly linked with seasonal pulses of epipelagic production. This is the first report on the biochemical composition of most of the amphipod and mysid taxa presented here.     

Composition and distribution of benthic isopod (Crustacea,Malacostraca) families off the Victoria-Land Coast (Ross Sea,Antarctica)

The benthic fauna off the Victoria-Land-Coast, Ross Sea (Antarctica) was investigated during the 19th Italica expedition in February 2004. Samples were taken along a latitudinal transect from Cape Adare down to Terra Nova Bay at water depths ranging from 84 to 515 m. A Rauschert dredge was used at 18 stations to collect epi- and infaunal macrobenthos. 9,494 specimens of Isopoda were collected, representing 19 families. Desmosomatidae were the most abundant family (35,297 ind/1,000 m²), followed by Paramunnidae (23,973 ind/1,000 m²). Paramunnidae was the most frequent taxon and was collected at all stations, in contrast to the Desmosomatidae, which did not occur at any station off Cape Adare.     

Karyotype morphology in Hyperiella dilatata Stebbing 1888 (Amphipoda: Hyperiidae) from the Ross Sea (Antarctica)

Summary The chromosome complement and some karyological features were investigated in the pelagic amphipod Hyperiella dilatata Stebbing 1888 from the Ross Sea (Antarctica). The diploid karyotype consists of 48 metacentric and 10 submetacentric elements (2n = 58). The presence of secondary constrictions and supernumerary chromosomes is described. Available chromosome numbers of Hyperiidea exhibit a wide range of distribution, among which Hyperiella dilatata is the closest to the modal number of other amphipods.     

Ectoenzymatic ratios in relation to particulate organic matter distribution (Ross Sea,Antarctica)

The results of a study on ectoenzymatic activity (the enzyme activity bound to particles larger than 0.2 micro m) and its relation to organic particle concentration are reported here. The sampling was carried out during the 1994 Antarctic spring, at a fixed station (Station 11) in the polynya of the Ross Sea, an area characterized by quick changes in sea ice cover. The sampling was repeated 4 times over a 20-day time period. The particulate organic matter distribution followed the physical structure of the water column, which depends on ice dynamics and is mainly determined by salinity. In the mixed-water surface layer (0-50 m) the concentrations were higher (on average 65.6 micro gC/L) than in the deeper water layer (50 m-bottom) (on average 19.1 micro gC/L). This distribution and quality, expressed by the protein:carbohydrate ratio, linked the particulate organic matter to the phytoplanktonic bloom which was in progress in the area. We determined the kinetic parameters of the glycolytic and proteolytic ectoenzymes and also the total activity for the proteolytic enzyme, in order to evaluate the contribution of the particle-bound activity. We observed higher values in the surface layer than in the deeper layer. b-Glucosidase activity ranged between 0.03 and 0.92 nmol L(-1) h(-1); b-N-acetylglucosaminidase activity was in the range of 0.04-0.58 nmol (L-1) (h-1). The total proteolytic activity (leucine aminopeptidase) ranged between 0.85 and 33.71 nmol L(-1) (h-1). The ectoproteolytic activity was about 35-60% of the total. The Km values were slightly higher for the proteolytic activity (on average 0.43 micro M for ectoproteolytic activity and 0.58 micro M for total proteolytic activity) than for the b-glucosidase (on average 0.36 micro M) and b-N-acetylglucosaminidase (on average 0.17 micro M), showing no remarkable variations in the water column. The ectoenzymatic ratios and their relationship with particulate organic substrates confirm the close link between organic substrate availability and degradation system response. The significant and positive correlations are not specific and suggest a prompt and efficient systemic response to the input of trophic resources. Nevertheless, changes in ectoenzyme activity and synthesis may act as adaptive responses to changing features of the ecosystem. In particular, variations in the proteolysis:glycolysis ratio depend on the functional features of the ecological system. In our study area this ratio is higher (about 10 or more) during production (particularly autotrophic) and lower (about 5 or less) during degradation/consumption events. The analysis of previous data, collected over a larger area characterized by different environmental conditions due to the changes of the pack ice cover, during the same cruise, confirms the existence of a significant relationship. Furthermore, the analysis of enzyme-uptake systems, expressed as Vmax:Km ratio, suggests that glycolytic ectoenzymes, although poorly expressed, may encourage microconsumers to grow rapidly on a wide range of organic substrates, including the refractory ones such as cellulose and chitin. However, low ectoenzyme potential exploitation rates of available organic substrates (on average about 5% for glycolytic and 12% for proteolytic ectoenzymes) would suggest that, during spring, zooplankton grazing or vertical and lateral transport are likely to play an important role in the removal of organic materials from the system.     

Aplanochytrium stocchinoi: a new Labyrinthulomycota from the southern ocean (Ross Sea, Antarctica)

Aplanochytrium stocchinoi, a new species of Labyrinthulomycota, is described from samples collected in Antarctica. Ultrastructural, life cycle and molecular data characterizing the new taxon are provided and compared with the features of other species included in the genus Aplanochytrium. The phylogenetic position of A. stocchinoi is investigated using the 18S rDNA as molecular marker and applying maximum parsimony, minimum evolution and maximum likelihood methods.     

Organic-matter degradative potential of Halomonas glaciei isolated from frazil ice in the Ross Sea (Antarctica)

Halomonas glaciei isolated from frazil ice in the Ross Sea (Antarctica) during austral summer 2003 was phenotypically characterized and its capability of degrading organic matter was tested. We evaluated specific bacterial growth rates (mu) to understand at which temperatures bacterial growth shows a linear and direct relationship with the available substrate (4-22 degrees C) and afterwards we tested H. glaciei growth curves and degradative potential at 0, 10 and 37 degrees C using two different media (one enriched and one depleted in PO(4)). The strain grew exponentially only at 10 degrees C. The fastest hydrolysis rates were expressed by enzymes aimed at polysaccharide degradation (alpha-d-glucosidase, beta-d-glucosidase and beta-d-galactosidase) while alkaline phosphatase and aminopeptidase activities were rather low. Our data suggest a preferential demand for carbon derived from carbohydrates rather than from proteins: ectoenzyme activities transformed into carbon mobilization from organic polymers, showed that the total carbon potentially released from polysaccharides can be almost one order of magnitude higher than the protein carbon mobilization. Principal component analysis of the enzyme affinity separated the six experimental conditions, highlighting how different physical (temperature) and chemical (PO(4) enrichment or depletion) features actively lead to a differentiation in the efficiency of the ectoenzymes produced, resulting in preferential degradation of diverse kinds of organic substrates.     

Distribution and composition of particulate organic matter in the Ross Sea (Antarctica)

The biochemical composition and spatial distribution of particulate organic matter (POM) were studied in the Ross Sea (Antarctica) in summer 1989 to assess the quantitative role of organic carbon fractions in the cycling of organic matter in the water column. Large differences in chemical composition were observed between surface and deep layers. The results indicated that, despite large geographical differences, POM was quite homogeneous, of phytoplankton origin and mostly detrital. Different ratios were used to investigate the changes in biochemical composition of particulate organic matter in relation to the ice-melting: CN (organic carbonorganic nitrogen ratio) and C-POMPOC (sum of carbohydrate, protein and lipid carbontotal organic carbon ratio) were used to analyse the percentage of refractory organic material. PPRTPCHO (proteincarbohydrate ratio) were used to establish POM age and RNADNA ratios as a relative measure of particulate activity; POCChl a and N-PPRTChl a ratios were used to estimate the autotrophic contribution to the suspended particulate organic matter. Despite its low caloric value (5.3 Kcal g POM^–1), an high caloric content in the photic layer (1.6 Kcal m^–3 of POM and 2.5 Kcal m^–3 of POC) was found thus indicating that a large amount of food was available to higher trophic levels.     

Late Quaternary foraminiferal assemblages from western Ross Sea (Antarctica) in relation to the main glacial and marine lithofacies

Investigations on foraminifers from Upper Pleistocene–Holocene sediments were carried out on twelve cores from the western Ross Sea continental margin (Drygalski, Joides, North Victoria Land Basins) as part of a “Progetto Nazionale di Ricerche in Antartide” (P.N.R.A.) multidisciplinary project. Data on the foraminiferal frequency, species diversity, tests abundance and their state of preservation were presented as a synthesis of 404 core samples to establish their relationships with the main glacial and marine lithofacies of this area. A total of 126 benthic species, pertaining to 73 genera have been identified; just few taxa, such as Cibicides spp., Globocassidulina spp., Trifarina angulosa and Miliammina spp. being the most ubiquitous and in some cases the dominant species of these paleoenvironments. Two variants of Neogloboquadrina pachyderma, including thin and thick-shelled forms have been recovered. We propose to use these results to provide the degree of glacial control during the Last Glacial Maximum and the following Holocene retreat of the ice sheets. High test fragmentation, low diversity and density tests reflect higher glacial influence of the ice sheet in the Drygalski Basin, whereas the decreasing percentage of fragmentation and a relative increase of density and diversity in Drygalski, Joides and North Victoria Land Basins indicate the paleoenvironmental passage from the ice sheet to the ice shelf condition. The ice shelf retreat is well evidenced in the Joides Basin by a succession of levels barren of foraminifers alternating with high-density levels, rich in T. angulosa, followed by a total disappearance of the calcareous foraminifers. Open-marine settings indicative of lower glacial influence and increased corrosiveness of the water masses is testified by the Miliammina foraminiferal assemblage during the Holocene in Drygalski and Joides Basins cores. On the contrary, rich and abundant benthic and planktonic assemblages characterize the Holocene paleoenvironment of the North Victoria Land area, indicating that the water masses were less corrosive with respect to the other areas. In addition to the glacial reworking of the tests, and the dissolution due to the corrosive water mass conditions, the volcaniclastic sediments recovered in the North Victoria Land Basin cores also affected the condition of test preservation. In volcaniclastic sediments, older than about 20 ka BP, the foraminifers concentration tends to zero and, when present, their tests are highly damaged or completely broken.     

Sea urchins, sea stars and brittle stars from Terra Nova Bay (Ross Sea, Antarctica)

Although echinoderms constitute some of the most conspicuous taxa of the Antarctic benthic communities, the echinoderm fauna of Terra Nova has not been described yet. The present study provides the first species list of echinoids, ophiuroids and asteroids from Terra Nova Bay (30–500 m depth) and describes the depth distribution of these species. Preliminary observations of the summer reproductive condition of some of the species are also included.     

Ultrastructure of muscle cells in Acetabulostoma (Crustacea, Ostracoda) – mussel shrimp from the Ross Sea (Antarctica)

Two new antarctic species of the genus Schizotricha Allman have been studied. The material comes from the Scotia Sea (Antarctica) and was collected by the Spanish antarctic expedition `Antártida 8611'. Both species are described and figured and the systematic position is discussed. A general survey of the geographical and bathymetrical distribution of the antarctic and subantarctic species of the genus is given. Finally, a key for the identification of the antarctic and subantarctic species of the genus, together with a comparative table including main features, are presented. Received: 4 April 1997 / Accepted: 18 July 1997     

Quantification of iceberg impact and benthic recolonisation patterns in the Weddell Sea (Antarctica)

Video transects in the eastern Weddell Sea were used to classify the mega-epibenthos into stages of recolonisation after iceberg impact and unaffected fauna. Three site categories differing in bottom topography and concentration of grounded icebergs were analysed. At small iceberg banks and on a comparatively plain seabed, 52-60% of undisturbed seafloor was found, and below 20% at a large iceberg bank. The impact was calculated as a function of values for recently disturbed areas and an estimated recovery time. The results show that, statistically, the Antarctic benthos never reaches peak maturity and that iceberg scouring is among the five most significant disturbances that any large ecosystem on earth experiences.