Measurements of buoyancy for some Antarctic notothenioid fishes from the South Shetland Islands

Buoyancy was measured for 258 specimens representing 13 species of adult and sub-adult nototheniids, bathydraconids, and channichthyids from the South Shetland Islands. Measurements were expressed as percentage buoyancy (%B)=W_water/W_air᎒². There were no neutrally buoyant species and mean values for %B were 3.07-6.11%, with channichthyids at the low end and benthic nototheniids and bathydraconids at the high end. All species showed an ontogenetic decrease in %B with increasing body weight. With the exception of Champsocephalus gunnari, there was no sexual dimorphism in %B within this sample. With some exceptions, values for %B were consistent with life-history information. Sub-adult Dissostichus mawsoni were not neutrally buoyant, as are large adults. Notothenia rossii had a significantly lower %B than closely related N. coriiceps. Benthic Gobionotothen gibberifrons had a lower %B than semipelagic Lepidonotothen larseni. Although they exhibit some diversification in life history, the four channichthyids in the sample were similar in %B. Neutral buoyancy is rare in notothenioids and may be confined to a single nototheniid clade.     

Ophiuroid community structure of the South Shetland Islands and Antarctic Peninsula region

During the BENTART 95 survey, epifauna was sampled with an Agassiz trawl at 24 stations ranging from north of Livingston Island (South Shetland Islands) to the Antarctic Peninsula at depths from 40 to 850 m. Four assemblages of ophiuroids were identified and correspond to Deception Island, Trinity Island, and the southern and northern zones of Livingston Island. In addition to these regions, gradients related to depth and filter-feeder biomass were found. The brittle-star assemblages were dominated by Ophionotus victoriae Bell, 1902, which to a large extent determine the biogeographic structure in the South Shetland Islands.     

Echiura from South Shetland Islands together with a review of its geographic distribution in the Antarctic Ocean

 Echiuran worms collected by the Spanish BENTART (=Bentos Antártico) cruises during years 1994 and 1995 to the South Shetland Islands from depths ranging from 24 to 1019 m are recorded. Three species are recognized: Alomasoma belyaevi, Echiurus antarcticus and Prashadus sp., with the presence of Prashadus sp. confirmed in the Antarctic. Distribution maps and a checklist of the echiuran species south of the Antarctic Convergence with depths and bibliographic references are included. Received: 10 July 1995/Accepted: 3 October 1995     

Population genetic structure of the Antarctic ascidian Aplidium falklandicum from Scotia Arc and South Shetland Islands

In sessile marine organisms, gene flow between populations depends mainly on free-living reproductive stages (such as larvae and gametes), and usually the strength of genetic structure is related to the time spent in the plankton and physical factors as oceanographic conditions. In Antarctica, abyssal depths that surround the continent and the Polar Front are considered strong barriers for benthic marine fauna, keeping the continent isolated from other shelves. The only available shallow water habitats between South America and the Antarctic continent are those around the Scotia Arc Islands; there are no shallow water habitats between the other southern continents and Antarctica. In this work, ISSRs-PCR markers were used to study the genetic structure of populations of Aplidium falklandicum, a compound ascidian with short-lived lecitotrophic larvae. A highly significant genetic differentiation (Φ_ST = 0.405; P < 0.05) and a pattern of isolation by distance were found. A genetic landscape approach identified a discontinuity in genetic diversity, coincident with the southernmost registered position of the Polar Front. For A. falklandicum, a species with presumably low capacity of long distance dispersal, the abyssal depths together with the large geographic distances create a barrier for gene flow.     

Distribution and diversity of soil protozoa in the McMurdo Dry Valleys of Antarctica

The polar desert soils of the McMurdo Dry Valley region support a limited water film community dominated by flagellates, amoebae, and nematodes. This study describes the protozoa and compares their distribution to nematodes. In 50 samples collected from 12 locations, rotifers and tardigrades were infrequent, and ciliates and testacea were rare. Soil protozoa occurred at all sites but the dominant nematode, Scottnema lindsayae (Timm 1971), did not, indicating soil habitat factors limiting nematode distribution are not limiting to protozoa. In contrast to the nematode species, which are all endemic to Antarctica, there were no endemic protozoan morphospecies found in our samples. The protozoan abundance was several orders of magnitude greater than that of the nematodes, and the species diversity was much greater. Most of the protozoa grew better at lower incubation temperatures. The ubiquitous distribution of protozoa suggests their importance in soil food webs and nutrient cycling in the dry valleys.     

Competition between the krill fishery and penguins in the South Shetland Islands

Among the South Shetland Islands, the potential competition for krill (Euphausia superba) between the Japanese fishery and krill-eating breeding penguins was assessed. A low level of competition was apparent due to several factors. Spatial overlap between the main fishing and foraging areas was insignificant. Firstly, the large colonies of the dominant penguin (chinstrap penguins,Pygoscelis antarctica) occurred where sea ice disappears early in spring, and not necessarily where krill are abundant in summer, i.e. the area of krill fishery. Secondly, overlap between trawling depth and foraging dive depth of penguins was marginal, with the latter depth being shallower. Moreover, overlap in the size-frequency of krill caught by trawlers and those captured by penguins was not complete; the penguins took larger krill on average. Finally, the present small fishery is unlikely to impact upon local krill biomass in the region. Krill biomass was estimated to be 250–1500 × 10³ tonnes within the preferred fishing areas during summer. The present catch rate by the fishery (≤13 × 10³ tonnes/half-month period) is smaller by an order of magnitude, and the fishing area does not include the main foraging areas of breeding penguins.     

Semi-quantitative study of macrobenthic fauna in the region of the South Shetland Islands and the Antarctic Peninsula

During the BENTART 95 Expedition, 24 Agassiz trawls for macrozoobenthos sampling were carried out at depths of 40–850 m, from north of Livingston Island to the Antarctic Peninsula. The samples were analysed using a semi-quantitative method, and with the resulting numerical data, transformed into a six-point scale, we constructed a Bray-Curtis similarity matrix. A total of 74,624 specimens, belonging to 38 taxonomic groups, were collected. The most abundant group was Polychaeta Sedentaria, with 36% of the total, whereas the highest relative masses were from Ascidiacea (23%), Echinoidea Regularia (18%) and Ophiuroidea (16%). The maximum number of specimens recorded was 15,600 ind./50 l. Cluster analysis separated stations located in Foster Bay (Deception Island), characterised by low taxonomic richness and high relative mass (average: 26.7 kg). A zonation of ascidians, regular sea urchins and ophiuroids was observed at Deception Island, clearly related to depth and substratum type. The remaining stations were separated into two groups. The first one comprised the shallowest stations (40–130 m), dominated by sessile active filter-feeders, belonging to Ascidiacea, Demospongia and Bryozoa, and probably related to high primary production zones. The second group comprised deeper stations and was dominated by classes exhibiting a diversity of trophic strategies: Ophiuroidea and Asteroidea, to 400 m, and Polychaeta Sedentaria at greater depths. Received: 20 February 1997 / Accepted: 8 September 1997     

Buoyancy studies of three morphs of the Antarctic fish Trematomus newnesi (Nototheniidae) from the South Shetland Islands

Phenotypic plasticity, a widespread phenomenon in boreal freshwater fishes, is less apparent in the marine realm and the organism–environment interactions producing this variation are undetermined. A sample of 40 specimens of Trematomus newnesi, an inshore Antarctic fish from King George/25 de Mayo Island in the South Shetlands, was composed of 52.5% typical morphs, 27.5% large-mouth morphs and 20% intermediate morphs. Measurements of percentage buoyancy on the morphs of this sample were 3.73, 3.84 and 3.83%, respectively with no significant differences among means. Both mean dry skeletal weight as a percentage of body weight and mean oral jaw weight as a percentage of dry skeletal weight were significantly greater in large-mouth morphs compared to typical morphs. Diversification in head and jaw morphology is not accompanied by diversification in ecology as represented by buoyancy and, in spite of external appearances, measurements of buoyancy offer no support for the hypothesis that the large-mouth morph is more benthic than the typical semipelagic morph. Although a trophic basis for this polymorphism is possible, it has not yet been documented. Our discussion centers on the status of key open questions regarding morphism and highlights areas requiring more research.     

Analysis of dietary overlap in Antarctic fish (Notothenioidei) from the South Shetland Islands: no evidence of food competition

A dietary overlap analysis between notothenioid species was carried out among three fish assemblages in the South Shetland Island area. Using Tyler's (1972) method, the re-occurrence of main and secondary prey among fish predators was 33% in summer and 37% over the year at Potter Cove, 25% in summer and 7% in winter at Admiralty Bay, and 20% in autumn/winter around Elephant Island. Likewise, using the "S" index of Linton et al. (1981), the diet similarity between most species pairs is <50%. This relatively low dietary overlap may be explained by the about equally divided occurrence of generalised feeders and specialised feeders, with no evidence of competition among them. The fishes' trophic niches seem to be separated by depth and prey taxa. These findings are compared with other Antarctic fish communities and those in similar non-Antarctic cold marine ecosystems.     

The winged Antarctic midge Parochlus steinenii (Gerke) (Diptera: Chironomidae) in the South Shetland Islands

The morphological variation of adult Parochlus steinenii (Gerke) is described from measurements of two populations from the South Shetland Islands. Morphologically, the population from Ardley Island is significantly larger than the population from Livingston Island, and in both populations variation in forefemur length is generally greater than variation in either antennal or wing length. The final instar larva of P. steinenii is described in detail. A consideration of the species' distribution in three geographically isolated areas, as well as of the greater morphological variation in polar as opposed to temperate populations, indicates that a flexible life history strategy in the larval stage may be important for survival in extreme environments.     

Dilution-to-Extinction Culturing of Psychrotolerant Planktonic Bacteria from Permanently Ice-covered Lakes in the McMurdo Dry Valleys,Antarctica

Lakes in the McMurdo Dry Valleys of Antarctica are characterized by a permanent ice cover and little or no anthropogenic influence. Although bacterial cultures have been obtained from these habitats, recent culture-independent studies indicate that the most abundant microbes in these systems are not yet cultivated. By using dilution-to-extinction cultivation methods with sterilized and nutrient-amended lake water as media, we isolated 148 chemotrophic psychrotolerant bacterial cultures from fresh surface water of Lake Fryxell and the east lobe of Lake Bonney and the hypersaline, suboxic bottom water from the west lobes of Lake Bonney. Screening of the 16S ribosomal ribonucleic acid (rRNA) genes of the cultures by restriction fragment length polymorphism (RFLP) yielded 57 putatively pure psychrotolerant, slow growing cultures grouped into 18 clusters. The sequencing of 16S rRNA genes of randomly selected representatives of each RFLP cluster revealed that the corresponding isolates belong to the Alphaproteobacteria (six RFLP patterns), Betaproteobacteria (six RFLP patterns), Bacteroidetes (four RFLP patterns), and Actinobacteria (two RFLP patterns). Phylogenetic analysis of the sequences showed that the vast majority of the isolates were not closely related to previously described species. Thirteen of 18 RFLP patterns shared a 16S ribosomal deoxyribonucleic acid sequence similarity of 97% or less with the closest described species, and four isolates had a sequence similarity of 93% or less with the nearest described species. Phylogenetic analysis showed that these sequences were representatives of deeply branching organisms in the respective phylum. A comparison of the isolates with 16S rRNA clone libraries prepared from the same environments showed substantial overlap, indicating that dilution-to-extinction culturing in natural lake water media can help isolate some of the most abundant organisms in these perennially ice-covered lakes.     

Distribution of organic carbon and nitrogen in surface soils in the McMurdo Dry Valleys, Antarctica

The organic carbon and nitrogen contents of sediments in the upper 2 cm of the soils surrounding several lakes in the McMurdo Dry Valleys were measured in a relatively high-density sampling grid, in order to better understand the present-day distribution of organic matter in the ecosystem that is most readily transportable via aeolean processes. Carbon and nitrogen contents of the bulk sediments and size-differentiated sediments decreased in a series according to lake basins oriented along the Taylor Valley's main axis (Lake Fryxell > Hoare ≥ west lobe Bonney ≥ east lobe Bonney). Samples were also obtained around Lake Vida and showed this basin to contain less organic matter than those in the Taylor Valley. This regional spatial analysis supports the emerging view that each basin provides distinct environments for in situ microbial activity, lithogenic weathering, aeolian deposition and sorting that can be detected through synoptic sampling. Accepted: 2 August 1999     

Demersal fish parasite fauna around the South Shetland Islands: high species richness and low host specificity in deep Antarctic waters

A total of nine Antarctic fish species belonging to five families were examined for their endohelminth parasite fauna. The fishes Parachaenichthys charcoti (Bathydraconidae), Chaenocephalus aceratus (Channichtyidae), Paradiplospinus gracilis (Gempylidae), Muraenolepis microps (Muraenolepididae), Gobionotothen gibberifrons, Lepidonotothen larseni, L. nudifrons, L. squamifrons, and Trematomus eulepidopus (Nototheniidae) were caught between 80 and 608 m trawling depth off the Antarctic Peninsula (Elephant Island, King George Island) in 1996. Nineteen different parasites species comprising five Digenea, two Cestoda, four Nematoda, and eight Acanthocephala were found. Pseudophyllidean cestodes, the nematodes Contracaecum radiatum and C. osculatum as well as the acanthocephalan Corynosoma bullosum were the most common, infesting eight of the fish species studied with prevalences reaching 100%. Pseudoterranova decipiens s.l. was the only parasite that was isolated from all studied fish species; however, at a lower intensity. The observed parasite host specificity was low, and the species richness in a single fish ranged from one to eleven in a C. aceratus. This icefish and the moray cod M. microps were the most heavily infested fish, harbouring many adult and larval parasitic stages. The benthodemersal P. gracilis had only two larval parasite species, while the nototheniids had very similar parasite communities, harbouring a total of 8–14 species. Larval mammalian parasites were found to utilize fish, especially the nototheniids and channichthyids, as a common transmission route into their final hosts. The fish parasites parallel explored different benthic host systems to reach the most suitable host. In contrast to the coast and continental shelf, the meso/bathypelagiac zone appears to be species poor and is inhabited by few larval forms. The fish parasite fauna off the South Shetland Islands can be characterized by generalistic parasites that distribute within Antarctic waters according to the feeding ecology and depth range of their teleost hosts, not only horizontally but also extending vertically into the deep sea.     

Biomineralization of endolithic microbes in rocks from the McMurdo Dry Valleys of Antarctica: implications for microbial fossil formation and their detection

In some zones of Antarctica's cold and dry desert, the extinction of cryptoendolithic microorganisms leaves behind inorganic traces of microbial life. In this paper, we examine the transition from live microorganisms, through their decay, to microbial fossils using in situ microscopy (transmission electron microscopy, scanning electron microscopy in back-scattered electron mode) and microanalytical (energy dispersive X-ray spectroscopy) techniques. Our results demonstrate that, after their death, endolithic microorganisms inhabiting Commonwealth Glacier sandstone from the Antarctica McMurdo Dry Valleys become mineralized. In some cases, epicellular deposition of minerals and/or simply filling up of empty moulds by minerals leads to the formation of cell-shaped structures that may be considered biomarkers. The continuous deposition of allochthonous clay minerals and sulfate-rich salts fills the sandstone pores. This process can give rise to microbial fossils with distinguishable cell wall structures. Often, fossilized cell interiors were of a different chemical composition to the mineralized cell walls. We propose that the microbial fossil formation observed was induced by mineral precipitation resulting from inorganic processes occurring after the death of cryptoendolithic microorganisms. Nevertheless, it must have been the organic template that provoked the diffusion of mineral elements and gave rise to their characteristic distribution pattern inside the fossilized cells.     

Raman spectroscopy of pigments and oxalates in situ within epilithic lichens: Acarospora from the Antarctic and Mediterranean

The effects of ambient and elevated ozone levels on growth and photosynthesis of beech ( Fagus sylvatica ) were studied by exposing seedlings in open-top chambers for one growing season to three treatments: charcoal-filtered (CF), non-filtered (NF) and non-filtered air with addition of ozone (30 ppb ozone) on clear days for 8–10 h d⁻¹ (NF +). Ambient levels were relatively low and accumulated to an AOT40 (accumulated exposure over a threshold of 40 ppb) of 4055 ppb h (for the period 23 Apr–30 Sept). The NF + chambers received an AOT40 of 8880 ppb h. Throughout the growing season we measured growth and photosynthetic properties. The treatments did not cause strong effects: measurements of gas exchange (light-saturated assimilation rate, CO₂ and light-response curves) and chlorophyll fluorescence showed slight and mostly non-significant reductions of several parameters. No significant differences were found for growth, though in the NF + treatment (AOT40 8880 ppb h) the relative growth rate for diameter increment was at times reduced by 12% compared with the control treatment.     

The Occurrence of Lysogenic Bacteria and Microbial Aggregates in the Lakes of the McMurdo Dry Valleys,Antarctica

The McMurdo Dry Valleys of Antarctica form the coldest and driest ecosystem on Earth. Within this region there are a number of perennially ice-covered (3–6 m thick) lakes that support active microbial assemblages and have a paucity of metazoans. These lakes receive limited allochthonous input of carbon and nutrients, and primary productivity is limited to only 6 months per year owing to an absence of sunlight during the austral winters. In an effort to establish the role that bacteria and their associated viruses play in carbon and nutrient cycling in these lakes, indigenous bacteria, free bacteriophage, and lysogen abundances were determined. Total bacterial abundances (TDC) ranged from 3.80 × 10⁴ to 2.58 × 10⁷ cells mL^–1 and virus-like particle (VLP) abundances ranged from 2.26 × 10⁵ to 5.56 × 10⁷ VLP mL^–1. VLP abundances were significantly correlated (P < 0.05) with TDC, bacterial productivity (TdR), chlorophyll a (Chl a), and soluble reactive phosphorus (SRP). Lysogenic bacteria, determined by induction with mitomycin C, made up between 2.0% and 62.5% of the total population of bacteria when using significant decreases and increases in TDC and VLP abundances, respectively, and 89.5% when using increases in VLP abundances as the sole criterion for a successful induction event. The contribution of viruses released from induced lysogens contributed <0.015% to the total viral production rate. Carbohydrate and protein based organic aggregates were abundant within the water column of the lakes and were heavily colonized by bacteria and VLPs. Alkaline phosphatase activity was detected within the matrix of the aggregates, implying phosphorus deficiency and consortial nutrient exchanges among microorganisms.     

Trophic relationships between the kelp gull and the Antarctic limpet at King George Island (South Shetland Islands, Antarctica) during the breeding season

The diet of the kelp gull (Larus dominicanus), its foraging behaviour and the consumption rates on the Antarctic limpet (Nacella concinna) were studied during austral spring and summer 1992/1993 and 1993/1994 at Potter Peninsula, King George Island, Antarctica. Prey information was obtained by collecting 237 pellets, foraging behaviour was observed by focal and instantaneous scan samplings, and consumption rate was estimated by means of weekly sampling of limpets found in 5 nests and their respective middens. Limpets were the most important prey followed by scavenged prey (penguin and seal carcasses), amphipods, snails, fish and euphausiids. Foraging gulls spent 51% of the time searching for limpets, 10% moving between foraging areas, 9% in catching effort and 15% handling prey. The number of gulls observed searching for limpets was inversely correlated with the tidal height. In the diet limpets provide 102.3, 159.4 and 188.1 kJ gull⁻¹ day⁻¹ during incubation, hatching and brooding respectively; these values range between 15 and 27%, with a maximum of 40%, of the basic daily energy requirements of kelp gulls. Total consumption rate estimations for the whole population of gulls at Potter Peninsula reached between 3400 and 4800 limpets day⁻¹, which represents approximately 10–14% of the total annual limpet mortality. Received: 25 March 1996 / Accepted: 26 August 1996     

16S rDNA diversity of cultured and uncultured prokaryotes of a mat sample from Lake Fryxell, McMurdo Dry Valleys, Antarctica

The prokaryotic diversity of aerobic and anaerobic bacterial isolates and of bacterial and archaeal 16S rDNA clones was determined for a microbial mat sample from the moated region of Lake Fryxell, McMurdo Dry Valleys, Antarctica. Among the anaerobic bacteria, members of Clostridium estertheticum and some other psychrotolerant strains dominated whereas methanogens and other Archaea were lacking. Isolates highly related to Flavobacterium hibernum, Janthiniobacterium lividum, and Arthrobacter flavus were among the aerobic bacteria most frequently isolated. Assessment of more than 350 partial 16S rDNA clone sequences of libraries generated by Bacteria- and Archaea-specific PCR primers revealed a rich spectrum of bacterial diversity but only two different archaeal clone sequences. Among the Bacteria, representative sequences belonged to the class Proteobacteria, order Verrucomicrobiales, class Actinobacteria, Clostridium/Bacillus subphylum of Gram-positives, and the Cytophaga-Flavobacterium-Bacteroides phylum. The clones formed about 70 higher taxonomy groups (<98% sequence similarity) and 133 potential species, i.e., groups of clones sharing greater than 98% similarity. Only rarely were clone sequences found to be highly related to Lake Fryxell isolates and to strains of described species. Subsequent analysis of ten sequencing batches of 36 individual clones indicated that the diversity might be still higher than had been assessed.