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.     

Dietary overlap among early juvenile stages in an Antarctic notothenioid fish assemblage at Potter Cove,South Shetland Islands

To date, studies of food overlap in Antarctic fish have been performed on a mixture of late juvenile and adult stages, leaving the young immature specimens (TL ≤ 10 cm) practically unexplored. We studied diet overlap and potential competition among early juvenile individuals in a coastal notothenioid community at Potter Cove, by analysing the stomach contents of 225 fish of 5 species collected in the summer of 2009–2010. We used frequency of occurrence (F %) and the coefficient “Q” for diet evaluation and the method of Tyler and the similarity index “S” for food overlap. Amphipods of the suborder Gammaridea were the main (Q > 2.900) and most frequent (% F) prey for all species, although Notothenia coriiceps also consumed gastropods of the family Littorinidae, mostly Laevilitorina antarctica. Secondary prey were algae for Notothenia rossii and N. coriiceps, calanoid (pelagic) and harpacticoid (benthic) copepods for Trematomus newnesi and the latter copepods and isopods of the family Munnidae for Lepidonotothen nudifrons. The reoccurrence of prey among fish species was 39.6 % and food overlap between 90 % of species pairs was under 58 %. Because similarly low values of diet overlap were reported for intermediate/advanced juveniles and adults of the same species at the same site, we conclude that there is no difference in the degree of interspecific food overlap and therefore potential competition between the immature and mature fraction of the fish community. Food competition is avoided by resource partitioning along a depth gradient or by different prey species.     

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.     

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.     

Prokaryotic assemblages in the maritime Antarctic Lake Limnopolar (Byers Peninsula,South Shetland Islands)

Extremophiles - The potentially metabolically active components within the prokaryotic assemblages inhabiting the Antarctic Lake Limnopolar (Byers Peninsula, Maritime Antarctica) were investigated...     

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.     

The contrasting diet of Harpagifer antarcticus (Notothenioidei, Harpagiferidae) at two localities of the South Shetland Islands, Antarctica

The diet of Harpagifer antarcticus was studied at two localities of the South Shetland Islands, Antarctica. The analysis of the stomach contents of specimens collected in tide pools at Potter Cove, King George Island, indicated that gammarid amphipods (mainly Gondogeneia sp.) were the main prey of this fish, followed by polychaetes, gastropods and isopods. By contrast, the specimens from Harmony Point, Nelson Island, which were recovered from stomach contents of Antarctic shags Phalacrocorax bransfieldensis feeding at depths of 46–110 m, preyed almost exclusively on the Antarctic krill Euphausia superba. These results are discussed and compared with previous studies. Received: 27 August 1997 / Accepted: 17 November 1997     

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.     

Phenotypic plasticity in the Antarctic fish <Emphasis Type="Italic">Trematomus newnesi</Emphasis> (Nototheniidae) from the South Shetland Islands

The presence of the two morphs, “typical” and “large mouth”, in the Antarctic fish species Trematomus newnesi (Perciformes, Notothenioidei) was recorded for the first time in nearshore waters of the South Shetland Islands (Potter Cove) and western Antarctic Peninsula (Petermann Island). The two morphs were distinguishable in specimens of 60–241 mm total length (TL); about 30% of the specimens constituted intermediate forms. In addition to the previously known characters separating the morphs, we found that the “relative size of the eye” can also be used to identify smaller and larger fish of the typical morph. The ecological significance of the two morphs remains unclear. Ratios of diagnostic characters for identification of the species at two size ranges (60–131 and 132–241 mm TL) are provided.     

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.     

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     

Molecular evidence for the origins of Antarctic fishes: paraphyly of the Bovichtidae and no indication for the monophyly of the Notothenioidei (Teleostei)

The notothenioids are an Antarctic suborder of perciform fishes to which increasing interest is being devoted. To investigate their origin, one must address two questions. First, are Bovichtidae (Bovichtus, Cottoperca, Pseudaphritis), the sister-group of the rest of the suborder, monophyletic ? Secondly, what is the sister-group of the Notothenioidei ? These questions were addressed by determining the complete nucleotide sequence of the D2 and D8 domains of 28S rDNA (759 sites, among which 158 informative for parsimony), for 6 notothenioids and a collection of 6 outgroup taxa including the Trachinoidei and Zoarcoidei. Different outgroups (or combinations of outgroups) and different weighting schemes support the inference that Pseudaphritis is closer to the rest of the Notothenioidei than Cottoperca and Bovichtus are. Relationships of Cottoperca and Bovichtus remain unclear with respect to outgroups. Our molecular data therefore clearly show that the Bovichtidae are paraphyletic, but their relationships are not those suggested by Balushkin in 1992. Our data provide no indication of the monophyly of the Notothenioidei in its classical sense. Most of the homoplasy is due to outgroup sequences and interrelationships of outgroups are unresolved. Some morphological synapomorphies shared by Pseudaphritis and the rest of the non-bovichtid Notothenioidei are proposed, including some that were identified by Voskoboynikova in 1993.     

Planktonic ostracods (Crustacea) along the coasts of the South Shetland Islands King George and Elephant (Antarctic Ocean) during spring season 1994

Ostracod samples were taken from coastal waters of the South Shetland Islands (King George and Elephant) northeast of the Antarctic Peninsula. The population structure of the planktonic ostracods in the upper 200-m water column is described. In total 77 samples were taken quantitatively by RMT-1 hauls predominantly containing Alacia hettacra, A. belgicae and Metaconchoecia isocheira. The dominance of A2, A1 and adult stages supports Kock's conclusion of an upward-directed ontogenetic migration. Received: 19 December 1996 / Accepted: 24 March 1997     

Analysis of trace metals in the Antarctic host-parasite system Notothenia coriiceps and Aspersentis megarhynchus (Acanthocephala) caught at King George Island,South Shetland Islands

Concentrations of the elements Al, Ag, As, Ba, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb and Sr were analysed by high-performance quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) in the acanthocephalan Aspersentis megarhynchus and in different tissues of its final host, Notothenia coriiceps. Infected fish were sampled at King George Island, South Shetland Islands, Antarctica. Most of the elements were found at significantly higher concentrations in the acanthocephalan than in muscle, liver and intestine of its host. Only Fe was concentrated in fish liver to a significantly higher level than in the parasite. Compared with the host tissues, the highest accumulation rates in A. megarhynchus were found for Pb, Cd, Ag, Ni and Cu. The acanthocephalans showed very high Ag and Pb levels, whereas the concentrations in the fish tissues were close to the detection limit. This study is the first proof that the enormous heavy-metal accumulation capacity reported for acanthocephalans from freshwater fish also occurs in acanthocephalans parasitizing marine fish. Consequently, acanthocephalans can be used to assess the occurrence and availability of even the lowest metal concentrations in all kinds of aquatic habitats, including remote areas such as the Antarctic.     

Genetic structure of declining chinstrap penguin (Pygoscelis antarcticus) populations from South Shetland Islands (Antarctica)

Seabirds and their response to climate perturbations are important bioindicators of changes in Antarctic ecosystems. During 30?years of observations of two chinstrap penguin (Pygoscelis antarcticus) colonies, one on King George Island and the other on Penguin Island (South Shetland Islands, Antarctica), the size of the breeding populations decreased by 84 and 41?%, respectively. We applied analyses of amplified fragment length polymorphisms to study the genetic structure of the two populations and to evaluate the influence of the sudden population decrease. Our data indicate that there were only weak genetic differences between the populations, which were not strong enough to support the hypothesis of population differentiation. Weak genetic differences observed between the two populations seem not to be determined by selection processes. We hypothesize that the very low level of between-population genetic structure can be explained by some extent of genetic drift, which is largely compensated by gene flow. Moreover, the two populations seem to remain in a stationary state. Our results support the hypothesis of limited natal philopatry in chinstrap penguins. The observed decrease in population size is probably caused by emigration or a rise in juvenile mortality due to the increasing krill limitation of the marine food web. However, detailed research is required to address this issue.     

Postembryonic development of Nymphon unguiculatum Hodgson 1915 (Pycnogonida, Nymphonidae) from the South Shetland Islands (Antarctica)

Male specimens of the sea spider species Nymphon unguiculatum, carrying eggs, larvae and postlarvae in various stages of development, were collected off the South Shetland Island at water depths between 112 and 472 m in austral summer 2006/2007. Here, we describe the external morphology of four postembryonic stages (protonymphon, instar 1, instar 2, and instar 3) carried by these specimens. We found that (1) protonymphon larvae hatch from the eggs; (2) larvae and postlarval stages have yolk reserves and are characterized by a relatively large size (average body lengths of 0.46, 0.55, 0.65 and 0.73 mm in the successive stages); (3) postlarvae remain on the ovigerous legs of males during several moults; (4) a spinning apparatus is present; (5) the development of walking legs is sequential. The larval and postlarval development of N. unguiculatum is compared with that known from other pycnogonid species.     

Species diversity and assemblages of macrobenthic Mollusca from the South Shetland Islands and Bransfield Strait (Antarctica)

During the research program BENTART 95, carried out from 16 January to 4 February 1995 on board RV Hesperides, a semi-quantitative Agassiz trawl and quantitative Van-Veen grabs were used at 31 subtidal stations between 40 and 850 m depth around Livingston Island, at Deception Island and in the Bransfield Strait. These data were used to search for and analyse the malacological assemblages. Among the molluscs sampled were 1,786 individuals belonging to 70 species of Solenogastres, Gastropoda Prosobranchia and Opisthobranchia, Scaphopoda and Bivalvia. The values of Shannon-Wiener diversity index ranged between 0.00 (one specimen) and 3.95, while Pielou's evenness index varied between 0.0 and 1.00. The bivalve Thyasira cf. dearborni was the most abundant species (227 specimens). Species richness varied from 1 to 19 species. Diversity showed great variations at different stations. The clustering analysis applying the Bray-Curtis coefficient allowed species classification according to constancy and fidelity, and distinguished four groups of stations: one that gathers clearly the stations of the inner bay of Deception Island, excepting station 1, and the other three fitting the remaining stations, located north and south of Livingston Island and in the Bransfield Strait, and correlated with environmental factors (granulometric composition, organic matter and carbonates). Accepted: 18 July 2000     

Daily activity and minimum food requirements during winter for gentoo penguins (Pygoscelis papua) in the South Shetland Islands, Antarctica

Estimates of daily activity and consequent demand for food during winter are scarce for many polar seabirds, yet essential for assessing constraints on foraging effort, demand for food, and potential competition with local fisheries. We affixed archival temperature tags to gentoo penguins (Pygoscelis papua) from two colonies in the South Shetland Islands to measure the frequency, timing, and duration of foraging trips and to estimate minimum food requirements during winter. Foraging trip frequencies ranged from 0.85 to 1.0 trips day⁻¹ and were positively correlated with day length. Early winter foraging trips more closely matched day length than late winter foraging trips. The data suggest that individuals maximize foraging time during the early winter period, likely to recover body mass following the breeding season and molt. The more attenuated response of foraging trip durations to increasing day length in late winter may be related to differences in local resource availability or individual behaviors prior to the upcoming breeding season. Minimum food requirements also exhibited a seasonal cycle with a mid-winter minimum. On average, minimum food requirements were estimated at 0.70 ± 0.12 kg day⁻¹. Extrapolated to the regional population of gentoo penguins, winter food requirements by gentoo penguins were equivalent to roughly 33% of annual krill catches by commercial fisheries in the South Shetland Island region over the past decade. Current expansion of the gentoo population and the krill fishery in the southern Scotia Sea warrants continued monitoring of gentoo penguins during winter.