Interannual variability in the feeding of ice fish (Notothenioidei, Channichthyidae) in the southern Scotia Arc and the Antarctic Peninsula region (CCAMLR Subareas 48.1 and 48.2)

We have studied the annual variation in food intake of three sub-Antarctic ice fish species (Champsocephalus gunnari, Chaenocephalus aceratus, and Pseudochaenichthys georgianus) and three high-Antarctic ice fish species (Chionodraco rastrospinosus, Cryodraco antarcticus, and Chaenodraco wilsoni). Stomach content analyses were conducted during bottom trawl surveys around the South Shetland Islands in 1998, 2001, 2002, 2003, and 2007, the South Orkney Islands in 1999 and 2009, and off the north-western Antarctic Peninsula in 2002, 2006, and 2006/2007 in order to obtain further insight into the amount of food of Antarctic demersal fish consume during summer. Annual variation in food intake was comparatively low within an area in the krill-feeding species C. gunnari and C. wilsoni. Food intake was much more variable, by a factor of 2 or 3 among years and areas, in larger C. aceratus and C. antarcticus, which rely heavily on fish as their dietary source. Food consumption was intermediate in the two species P. georgianus and C. rastrospinosus, which rely on both krill and fish.     

Population divergences despite long pelagic larval stages: lessons from crocodile icefishes (Channichthyidae)

Dispersal via pelagic larval stages plays a key role in population connectivity of many marine species. The degree of connectivity is often correlated with the time that larvae spend in the water column. The Antarctic notothenioid fishes develop through an unusually long pelagic larval phase often exceeding 1 year. Notothenioids thus represent a prime model system for studying the influence of prolonged larval phases on population structure in otherwise demersal species. Here, we compare the population genetic structure and demographic history of two sub‐Antarctic crocodile icefish species (Chaenocephalus aceratus and Champsocephalus gunnari) from the Scotia Arc and Bouvet Island in the Atlantic sector of the Southern Ocean to delineate the relative importance of species‐specific, oceanographic and paleoclimatic factors to gene flow. Based on 7 (C. aceratus) and 8 (C. gunnari) microsatellites, as well as two mitochondrial DNA markers (cytochrome b, D‐loop), we detect pronounced population genetic structure in both species (amova FSTs range from 0.04 to 0.53). High genetic similarities were found concordantly in the populations sampled at the Southern Scotia Arc between Elephant Island and South Orkney Islands, whereas the populations from Bouvet Island, which is located far to the east of the Scotia Arc, are substantially differentiated from those of the Scotia Arc region. Nonetheless, haplotype genealogies and Bayesian cluster analyses suggest occasional gene flow over thousands of kilometres. Higher divergences between populations of C. gunnari as compared to C. aceratus are probably caused by lower dispersal capabilities and demographic effects. Bayesian skyline plots reveal population size reductions during past glacial events in both species with an estimated onset of population expansions about 25 000 years ago.     

Taxonomic studies of the Antarctic icefish genus Cryodraco Dollo, 1900 (Notothenioidei: Channichthyidae)

Based on a meristic and morphometric study of 101 specimens, we recognise 2 valid species in the Antarctic channichthyid genus Cryodraco: Cryodraco antarcticus Dollo, 1900 and C. atkinsoni Regan, 1914. Although the species overlap in most meristic and morphometric characters, we have distinguished several reliable characters for diagnosis and identification. Multidimensional scaling, a nonparametric multivariate technique, clearly separates the two species on the basis of pelvic fin length, head length, number of second dorsal fin rays and origin of the lower lateral line relative to the anal fin rays. We provide a revised identification key to the species of Cryodraco. From a zoogeographical point of view, C. antarcticus has a circum-Antarctic distribution whereas C. atkinsoni is largely confined to the East Antarctic Zoogeographic Province.     

A predatory fungus (Hyphomycetes: <Emphasis Type="Italic">Lecophagus</Emphasis>) attacking Rotifera and Tardigrada in maritime Antarctic lakes

Lecophagus antarcticus, described as a new species of predaceous Hyphomycete of rotifers and tardigrades, was collected from cyanobacterial mats and sediments at shallow lake margins on Signy Island, South Orkney Islands, Antarctica. The new species differs from similar Lecophagus species by larger, more robust vegetative hyphae and by producing septate conidiophore branches or conidiophores as terminals of lateral vegetative hyphae. This is the first report of this genus from either freshwater or polar regions.     

Life history strategies of the Scotia Sea icefish, <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis>, along the Southern Scotia Ridge

Reproductive capacity can influence distribution and abundance over large spatial scales through larval dispersal, even when adult stages remain isolated following settlement. We examined size distribution, reproductive traits and age structure in Scotia Sea icefish, Chaenocephalus aceratus, an abundant benthic species with a long larval pelagic phase found on continental shelves along the Southern Scotia Ridge. In particular, we compared life history strategies between fish caught during surveys undertaken off the South Orkney Islands (SOI) and South Shetland Islands (SSI). Results corroborated regional separation after settlement and suggested distinct life history strategies, in which fish from SOI invested much less in reproduction, and somewhat more in somatic growth earlier in their life history. Compared to SSI, body weight increased faster with length and absolute fecundity was 46 % lower and increased more slowly with size for SOI population. In addition, the proportion of spawning cohorts and L _∞ was lower and k higher for SOI. The differences appeared to be a phenotypic response to environmental conditions related to regional hydrography. Lower reproductive capacity around the SOI, and strong eastward flow in the large-scale circulation, suggests that the SSI may be more important in influencing distributions and abundance of icefish along the Southern Scotia Ridge.     

Isolation and characterization of eight microsatellite loci in the icefish Chaenocephalus aceratus (Perciformes,Notothenioidei, Channichthyidae)

We characterized eight polymorphic microsatellites in the Scotia icefish Chaenocephalus aceratus (Perciformes, Notothenioidei, Channichthyidae) that is endemic of Southern Ocean waters surrounding the tip of the Antarctic Peninsula. Microsatellites were isolated from a partial genomic library enriched for an AC motif. The number of alleles ranged from two to 19 with a mean observed hererozygosity of 0.71. Loci were in Hardy–Weinberg equilibrium and no evidence for linkage disequilibrium was found. These molecular markers will be useful to investigate Scotia icefish genetic structure, possibly providing insights on its effective population size and demographic history.     

Diet of two icefish species from the South Shetland Islands and Elephant Island,<Emphasis Type="Italic"> Champsocephalus gunnari</Emphasis> and<Emphasis Type="Italic"> Chaenocephalus aceratus</Emphasis>

The summer diet of two species of icefishes (Channichthyidae) from the South Shetland Islands and Elephant Island, Champsocephalus gunnari and Chaenocephalus aceratus, was investigated from 2001 to 2003. Champsocephalus gunnari fed almost exclusively on krill (Euphausia superba) in all years. The importance of other taxa (Themisto gaudichaudii, mysids, myctophids) in the diet was negligible. The average feeding rate of Champsocephalus gunnari inferred from an exponential gastric evacuation model was between 1.0 and 1.5% body weight per day. Most of the stomachs of Chaenocephalus aceratus were empty. Stomachs with food contained mainly krill, mysids and fish. Among the fish taken, locally abundant species formed the bulk of the diet: Gobionotothen gibberifrons in 2001, Lepidonotothen larseni and Champsocephalus gunnari in 2002 and L. larseni in 2003. An ontogenetic shift in feeding preference of Chaenocephalus aceratus was observed: fish smaller than 30 cm fed on krill and mysids, while larger animals relied primarily on fish.     

The diet of the South Georgia shag Phalacrocorax georgianus at South Orkney Islands in five consecutive years

The diet of the South Georgia shag Phalacrocorax georgianus at Laurie Island, South Orkney Islands, was studied by the analysis of 420 pellets (regurgitated casts) collected from the 1995 to 1999 breeding seasons. Demersal-benthic fish were by far the main prey, followed by molluscs (mainly octopods and bivalves) and polychaetes. Harpagifer antarcticus (in 1995, 1998, 1999) and Lepidonotothen nudifrons (1996, 1997) were the most frequent prey, followed by Gobionotothen gibberifrons or Trematomus newnesi. Harpagifer antarcticus, followed by L. nudifrons or T. newnesi, was the most numerous prey in all of the seasons and predominated in mass in 1995 and 1996, followed by Notothenia coriiceps and L. nudifrons. In 1997 and 1999, G. gibberifrons and N. coriiceps were the species that most contributed to the diet whereas N. coriiceps and H. antarcticus contributed most in 1998. Our results differ from those reported for the South Orkney Islands in previous studies. These differences could be due to the use of different diet-analysis methods and to shags-related and/or fisheries-related changes in the food availability around the colonies. These alternative explanations are analysed and discussed.     

The biodiversity and biogeography of the free-living nematode genera Desmodora and Desmodorella (family Desmodoridae) at both sides of the Scotia Arc

Samples taken at two stations in the northern and southern parts of the Scotia Arc, at depths of 277 and 307 m, respectively, were analysed for metazoan meiofauna with special attention to the nematodes. Identification to species level was performed for two closely related subdominant nematode genera (Desmodora and Desmodorella) in samples from the two Scotia Arc stations and in other available samples from adjacent areas (Magellan Region, Drake Passage, Weddell Sea). Seven Desmodora species and three Desmodorella species were found, of which, respectively five and two species are new to science. The Scotia Arc stations show relatively high densities and average diversity on meiofauna and nematode level compared to adjacent areas. The distribution patterns of the various Desmodora and Desmodorella species suggest the Scotia Arc as a shallow bridge and a possible exchange route for meiofauna between the Antarctic and South America, especially since these species seem to be constrained by water depth.     

Triacylglycerol lipase activities in tissues of Antarctic fishes

. The activity of the lipolytic enzyme, triacylglycerol lipase (TAG lipase; E.C. 3.1.1.3) was measured in heart ventricle, liver, oxidative skeletal muscle, and adipose tissue of four species of Antarctic fishes (Chaenocephalus aceratus, Notothenia coriiceps, Trematomus newnesi, Gobionotothen gibberifrons). Estimates of weight-specific activities at 0°C in tissues of the Antarctic fishes were broadly comparable to those reported for temperate-zone fish species assayed at their physiological temperature. Within each species, liver tissue displayed the highest weight-specific activity of TAG lipase in C. aceratus, T. newnesi, and G. gibberifrons, while adipose tissue of N. coriiceps showed the highest activity within that species. Combining these estimates with carefully measured somatic indices of the tissues, permitted assessment of the relative importance of different tissues to overall lipolytic capacity on an organismal level. On this basis, liver tissue displays the greatest capacity of TAG lipase per 100 g body weight in each of the species studied.     

Microsatellite analysis reveals genetic differentiation between year-classes in the icefish <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis> at South Shetlands and Elephant Island

Chaenocephalus aceratus is one of the most abundant Antarctic icefish species in the Atlantic sector and has been a by-catch species in the fishery for mackerel icefish, Champsocephalus gunnari, between the mid-1970s and mid-1980s at South Georgia, South Orkney, and South Shetland Islands. The species became the target of the fishery in particular seasons, such as at South Georgia in 1977/78. In our paper, we report results on genetic differentiation for 11 microsatellite loci in C. aceratus samples collected at the South Shetlands and Elephant Island. This study represents the first report on microsatellite variability of an icefish species. Our results support the evidence from previous studies on differences in infestation patterns of parasites that a single panmictic population of C. aceratus exists, spanning the two sampling sites separated by about 100 km. Moreover, our study indicates the presence of a significant genetic differentiation between individual year-classes pointing out the existence of dynamic processes acting at the population genetic level, according to recent results for broadly distributed marine species. Both small effective population size and immigration from unsampled differentiated stocks may be at the base of the differentiation found in C. aceratus. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Diversity, relative abundance, new locality records and population structure of Antarctic demersal fishes from the northern Scotia Arc islands and Bouvetøya

A primary objective of the ICEFISH 2004 cruise was to collect and study notothenioid fishes from remote localities in the Atlantic sector of the Southern Ocean. Nearly 1 month was devoted to bottom trawling for fishes on the shelf and upper slope (to 1,000 m) areas around Shag Rocks, South Georgia, South Sandwich Islands and Bouvetøya. The focus was on the latter two locations, because their faunas are more poorly known. Eight species were collected at Shag Rocks with Patagonotothen guntheri most abundant; 17 at South Georgia with Lepidonotothen nudifrons, L. larseni and Gobionotothen gibberifrons most abundant; 13 at the South Sandwich Islands with L. larseni, L. nudifrons and G. gibberifrons most abundant; and 11 at Bouvetøya with L. larseni, Macrourus holotrachys and L. squamifrons most abundant. Ten new locality records were established: Shag Rocks (1), South Georgia (1), South Sandwich Islands (5), South Sandwich Trench at 5,350 m (1) and Bouvetøya (2). Total known demersal fish diversity on the shelf and upper slope at Shag Rocks/South Georgia, South Sandwich Islands and Bouvetøya is 42, 31 and 17 species, respectively. To examine population structure in the four most abundant notothenioids at Bouvetøya (L. larseni, L. squamifrons, Notothenia coriiceps and Chaenocephalus aceratus), we examined the ND2 portion of mitochondrial DNA. Chaenocephalus aceratus, N. coriiceps and L. larseni exhibited no significant genetic differentiation in comparison with samples from localities in the Scotia Sea and the Antarctic Peninsula. However, L. squamifrons showed significant genetic differentiation between the South Shetlands and Bouvetøya populations (F _ST = 0.189, P = 0.015). Thus, these data combined with previous studies of two other notothenioids suggest that five of the six notothenioid species at Bouvetøya are not genetically differentiated from other localities in the Atlantic sector of the Southern Ocean. The location of Bouvetøya within the Antarctic Circumpolar Current and the long (1–2 years) pelagic stages of the notothenioids at Bouvetøya may be at least partly responsible for this genetic homogeneity.     

Age and early life history of juvenile scotia sea icefish, <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis>, from Elephant and the South Shetland Islands

The otolith microstructure of juvenile Scotia Sea icefish (Chaenocephalus aceratus) was analyzed from samples collected around Elephant and South Shetland Islands, with the aim to validate previous annual ageing and to give new insight into its early life history timings. Fish were caught by bottom trawl fishing conducted on the continental shelf between 100 and 500 m depth. To determine the timing and position of the first annulus on sagittal otoliths, microincrements were counted on juvenile otoliths previously aged 1+ year old by counting annuli in sectioned otolith. Assuming that microincrements were laid down daily, age ranged from 406 to 578 days in fish measuring 13–19 cm TL, thus corroborating previous results. The relationship between fish size and otolith size/weight was estimated using the least square linear regression method. The relationship between age and otolith size was also estimated to determine the otolith length in 1-year old fish, which was approximately 1.58 mm. In all samples the otolith core was characterized by an evident strong check, assumed to be laid down at the beginning of exogenous feeding of yolk sac larvae. The yolk sac duration estimated from hatch to the first feeding check was longer than other channichthyids, lasting 29–45 days. Hatching dates were backcalculated from the date of capture using the age estimates, indicating C. aceratus sampled off Elephant and South Shetland Islands hatched over a long period lasting from July to December, with a peak in November. As a result, the potential larval dispersion driven by local oceanographic features is discussed.     

Comparative population genetics of seven notothenioid fish species reveals high levels of gene flow along ocean currents in the southern Scotia Arc, Antarctica

The Antarctic fish fauna is characterized by high endemism and low species diversity with one perciform suborder, the Notothenioidei, dominating the whole species assemblage on the shelves and slopes. Notothenioids diversified in situ through adaptive radiation and show a variety of life history strategies as adults ranging from benthic to pelagic modes. Their larval development is unusually long, lasting from a few months to more than a year, and generally includes a pelagic larval stage. Therefore, the advection of eggs and larvae with ocean currents is a key factor modulating population connectivity. Here, we compare the genetic population structures and gene flow of seven ecologically distinct notothenioid species of the southern Scotia Arc based on nuclear microsatellites and mitochondrial DNA sequences (D-loop/cytochrome b). The seven species belong to the families Nototheniidae (Gobionotothen gibberifrons, Lepidonotothen squamifrons, Trematomus eulepidotus, T. newnesi) and Channichthyidae (Chaenocephalus aceratus, Champsocephalus gunnari, Chionodraco rastrospinosus). Our results show low-population differentiation and high gene flow for all investigated species independent of their adult life history strategies. In addition, gene flow is primarily in congruence with the prevailing ocean current system, highlighting the role of larval dispersal in population structuring of notothenioids.     

Chinstrap penguins (Pygoscelis antarctica) nesting on Sabrina Islet, Balleny Islands, Antarctica

Although the majority of chinstrap penguins (Pygoscelis antarctica) inhabit the Scotia Arc, a minuscule population of ten breeding pairs has been reported several times from Chinstrap Islet, in the Balleny Islands, 5,000 km distant on the opposite side of Antarctica. An aerial photographic census (December 2000) reveals that the overall penguin population of the Balleny Islands has declined by 8% since the last census 16 years ago, while the combined populations of the two largest colonies, Chinstrap Islet and Sabrina Islet, have increased by 11%. A ground visit confirmed for the first time that chinstrap penguins also breed on Sabrina Islet, occupying 20-24 nests on the margins of the Adélie colony (3,790 pairs in all). The small size and anomalous location of the Balleny Islands chinstrap population clearly warrant further study and the strongest protective measures.     

Microscopic anatomy and ultrastructure of the digestive system of three Antarctic shrimps (Crustacea: Decapoda: Caridea)

Mandibles and stomachs of three Antarctic shrimp species (Nematocarcinus lanceopes, Notocrangon antarcticus, and Chorismus antarcticus) were investigated by means of scanning electron microscopy. Transmission electron microscopy of the midgut glands was applied to find out the nutritional status of the animals, which contained a broad variety of food items in their stomachs. In contrast to the Antarctic krill, the three carideans possess a dual filter system; primary filters in the cardia and secondary filters in the pyloric chamber. Morphologically, the mandibles and stomachs of the three species vary considerably; however, their food items are similar. We conclude that stomach contents do not really reflect the different modes of life or habitat preferences of the investigated species.     

The diet of the Antarctic fur seal Arctocephalus gazella at Harmony Point, Nelson Island, South Shetland Islands

The diet of non-breeding male Antarctic fur seals (Arctocephalus gazella) was investigated at Harmony Point, Nelson Island, South Shetland Islands, by the analysis of 18 and 33 scats collected during February 1996 and 1997 respectively. Overall, fish were the most frequent prey (74.5%) and predominated by mass (54.4%), whereas krill predominated by number (94.2%). This coincides well with the pattern observed in 1997, but in 1996 krill was the most important prey by number and mass (50.2%). The importance of the remaining taxa represented in the samples (octopods, hyperiids and bivalves) was negligible. Among fish, myctophids represented 85.2% of the fish mass, with Gymnoscopelus nicholsi and Electrona antarctica being the main prey. These two species predominated in 1997, whereas the channichthyid Cryodraco antarcticus and the nototheniid Gobionotothen gibberifrons were dominant in 1996. The importance of the myctophids as prey of the Antarctic fur seal is discussed. Received: 7 October 1997 / Accepted: 24 May 1998     

Scotia Arc Acari: antiquity and origin

The Scotia Arc comprises South Georgia, South Sandwich, South Orkney and South Shetland Islands together with the Antarctic Peninsula. Free-living Acari of the Scotia Arc contain immigrant and endemic elements. Transport of immigrant species to and within the Maritime Antarctic has been via Holocene storms and ocean currents. Most immigrants are Gamasida, Oribatida and Acaridida while Actinedida dominate the endemic element. Immigrant species on South Georgia share common 'sub-Antarctic' affinities with South Indian and, to a lesser extent, South Pacific Ocean island faunas. In contrast, immigrants to the rest of the Scotia Arc and Bouvetøya on the mid-Atlantic Ridge, form a robust 'Maritime Antarctic' Province group. The endemic component is of largely Tertiary origin and, like that of Continental Antarctica, dominated by a few cosmopolitan families and genera of Actinedida. There are no bona fide pan-Antarctic species and little evidence that Continental and Maritime Antarctic faunas have a common ancestry, indeed the Continental endemic fauna is entirely montane while that of Maritime Antarctica is coastal. The presence of common Maritime Antarctic/South Pacific island genera corroborate the Antarctic Peninsula as being derived from a South Pacific island archipelago which collided with Continental Antarctica during the Tertiary period.     

Dietary composition of juvenile Dissostichus eleginoides (Pisces, Nototheniidae) around Shag Rocks and South Georgia, Antarctica

A diet analysis of the Patagonian toothfish Dissostichus eleginoides, trawled in the South Georgia Islands area in March–April 1996, was carried out by frequency of occurrence (F%) and coefficient Q (%) methods. The samples consisted chiefly of immature specimens, with predominant length ranges of 30–70 cm (TL). Fish was by far the main food on the shelves of Shag Rocks and South Georgia, accounting for about 70% of prey. Krill appeared as secondary food, although its importance was overestimated by the frequency of occurrence method. Cephalopods and mysids were infrequent in the stomachs, and only at Shag Rocks and South Georgia, respectively. Lepidonotothen kempi, Champsocephalus gunnari and Chaenocephalus aceratus constituted the main fish prey and their variability between Shag Rocks and South Georgia depended on their local abundance. The large proportion of fish exhibiting stomachs full or close to fullness (together 62%) suggests that feeding intensity of the species was high.