Spermatogenesis in some Antarctic teleosts from the Ross Sea: histological organisation of the testis and localisation of bFGF

Testis structure and spermatogenetic activity were studied in two Antarctic teleostean species, Chionodraco hamatus and Trematomus bernacchii, captured during the austral summer in the Ross Sea. The specimens of C. hamatus showed full reproductive activity but, the spermatogenetic cycle being over, only spermatogonia and Sertoli cells were present in the seminiferous tubules whereas the lumina were full of sperm. By contrast, the specimens of T. bernacchii were in the stage of spermatogenetical recrudescence, having not yet entered the reproductive period. In this species, the seminiferous tubules were devoid of lumen and full of spermatogonial cysts, showing some mitoses. Many tubules contained cysts of meiotic spermatocytes I and, in one case only, small cysts of spermatocytes II. The final stages of spermatogenesis were lacking, presumably occurring later, in autumn/winter. The immunocytochemical tests aimed at identifying bFGF and FGFR1 revealed a positive reaction both in Sertoli cells and spermatogonia in the C. hamatus specimens, indicating that this species was ready to start a new spermatogenetic cycle. The weak reaction in the specimens of T. bernacchii suggests that, in this species, the stage of cell division was over and that of meiosis and differentiation was starting. These data indicate that Antarctic fish have an opportunistic spermatogenetic cycle. Accepted: 24 October 1999     

Use of the lateral line and tactile senses in feeding in four antarctic nototheniid fishes

Synopsis Fishes of the family Nototheniidae (Pisces: Perciformes) dominate antarctic fish communities and have radiated to fill diverse niches. The most southern species must operate under an extended austral night and under thick sea ice, yet have eyes more typical of shallow coastal fishes. In winter, the eyes are probably useless, except for detecting bioluminescence. I compared the responses of four species to hydromechanical and tactile signals: two benthivores,Trematomus bernacchii andT. pennellii, a benthic planktivore,T. nicolai, andPagothenia borchgrevinki, which feeds near the ice undersurface and within ice cracks. The planktivores have dorsal mouths, with eyes oriented dorsally or laterally (Pagothenia); their lateral line canals and receptor organs are larger dorsally. The benthivores have more ventrally oriented mouths and eyes. All species responded to hydromechanical cues to the head, but only the two benthivores responded to trunk hydromechanical stimuli or tactile stimuli to the ventral trunk or pelvic fins. Possibly responses to plankton along the trunk are of little use if a reorientation washes pelagic prey away. In responding to trunk stimuli,T. bernacchii reorients its head to the target in two stages by slowly pivoting on its pelvic fins. In contrast,T. pennellii reorients in a single quick flip. It is argued that, becauseT. bernacchii has wider canals thanT. pennellii, it must move more slowly to reduce self-generated noise. It is likely that further studies of winter diet and prey behavior may reveal the relative advantages of the two repositioning styles.     

A relationship of diet to prey abundance and the foraging behavior of Trematomus bernacchii

Little information is available regarding fish diets in Antarctica and how they relate to prey availability. The primary objective of this work was to describe the diet of Trematomus bernacchii. The second objective was to compare prey taken with prey present in the benthos along a spatial gradient of prey abundance using Ivlev's Index of Electivity. All samples were collected from 4 different sites on the east side of McMurdo Sound, Antarctica. Fish were captured by divers at the same depth at each site and their stomachs were flushed for dietary analysis. The diet of T. bernacchii varied among sites, and prey selectivity varied inversely with prey abundance. Many of the prey taken by T. bernacchii were sedentary species suggesting that T. bernacchii is a hunt and peck predator.     

Competition and coexistance between Glossiphonia complanata and Helobdella stagnalis (Glossiphoniidae: Hirudinoidea)

Summary The prey utilization of Glossiphonia complanata and Helobdella stagnalis from Bruce Lake, Alberta, Canada was examined quantitatively using serological techniques. While considerable prey range overlap occurred between the species, niche overlap was low during the winter, peaked in March and declined through the summer. Temporal differences in feeding and intraspecific weight class differences in prey utilization were found in both species but more distinctly in G. complanata. It is suggested that co-existance of G. complanata and H. stagnalis is based on adjustments of weight class food resource partitioning on a temporal basis.     

Concentrations of Thirteen Trace Metals in Scales of Three Nototheniid Fishes from Antarctica (James Ross Island,Antarctic Peninsula)

In this study, we assessed concentrations of 13 trace metals in the scales of Notothenia coriiceps, Trematomus bernacchii and Gobionotothen gibberifrons caught off the coast of James Ross Island (Antarctic Peninsula). Overall, our results for scales broadly match those of previous studies using different fish and different organs, with most metals found at trace levels and manganese, aluminium, iron and zinc occurring at high levels in all species. This suggests that scales can serve as a useful, non-invasive bioindicator of long-term contamination in Antarctic fishes. High accumulation of manganese, aluminium, iron and zinc is largely due to high levels in sediments associated with nearby active volcanic sites. Manganese, vanadium and aluminium showed significant positive bioaccumulation in T. bernacchii (along with non-significant positive accumulation of iron, zinc, cobalt and chromium), most likely due to greater dietary specialisation on sediment feeding benthic prey and higher trophic species. Levels of significance in bioaccumulation regressions were strongly affected by large-scale variation in the data, driven largely by individual differences in diet and/or changes in habitat use and sex differences associated with life stage and reproductive status. Increased levels of both airborne deposition and precipitation and meltwater runoff associated with climate change may be further adding to the already high levels of manganese, aluminium, iron and zinc in Antarctic Peninsula sediments. Further long-term studies are encouraged to elucidate mechanisms of uptake (especially for aluminium and iron) and possible intra- and interspecific impacts of climate change on the delicate Antarctic food web.

     

Seasonal lipid contents of Antarctic microarthropods

A technique for the accurate determination of lipid content of very small quantities of biological tissue was applied to two Antarctic oribatid mites,Alaskozetes antarcticus andHalozetes belgicae, and a collembolan,Cryptopygus antarcticus. Analysis of monthly samples of the three species, collected between November 1989 and March 1991, revealed little evidence of any seasonal pattern of lipid deposition or use. MaleAlaskozetes were the only exception, showing very low lipid levels for a short period of the austral summer, followed by rapid deposition before the onset of winter. Mean lipid contents of the three species over the study period were 10–15% of mean dry weight. There was evidence of a seasonal pattern of egg formation and oviposition in bothAlaskozetes andHalozetes, but this was not reflected in the observed lipid levels. Feeding activity was mostly restricted to the summer months (November–March); a temporary resumption of feeding in winter (late August 1990) was followed by an increase in lipid content in both sexes ofAlaskozetes.     

Diet partitioning in sympatric Atlantic salmon and brown trout in streams with contrasting riparian vegetation

Prey intake by Atlantic salmon Salmo salar and brown trout Salmo trutta was measured across different riparian vegetation types: grassland, open canopy deciduous and closed canopy deciduous, in upland streams in County Mayo, Western Ireland. Fishes were collected by electrofishing while invertebrates were sampled from the benthos using a Surber sampler and drifting invertebrates collected in drift traps. Aquatic invertebrates dominated prey numbers in the diets of 0+ year Atlantic salmon and brown trout and 1+ year Atlantic salmon, whereas terrestrial invertebrates were of greater importance for diets of 1+ and 2+ year brown trout. Terrestrial prey biomass was generally greater than aquatic prey for 1+ and 2+ year brown trout across seasons and riparian types. Prey intake was greatest in spring and summer and least in autumn apart from 2+ year brown trout that sustained feeding into autumn. Total prey numbers captured tended to be greater for all age classes in streams with deciduous riparian canopy. Atlantic salmon consumed more aquatic prey and brown trout more terrestrial prey with an ontogenetic increase in prey species richness and diversity. Atlantic salmon and brown trout diets were most similar in summer. Terrestrial invertebrates provided an important energy subsidy particularly for brown trout. In grassland streams, each fish age class was strongly associated with aquatic, mainly benthic invertebrates. In streams with deciduous riparian canopy cover, diet composition partitioned between conspecifics with older brown trout associated with surface drifting terrestrial invertebrates and older Atlantic salmon associated with aquatic invertebrates with a high drift propensity in the water column and 0+ year fish feeding on benthic aquatic invertebrates. Deciduous riparian canopy cover may therefore facilitate vertical partitioning of feeding position within the water column between sympatric Atlantic salmon and brown trout. Implications for riparian management are discussed.     

Feeding plasticity of Trematomus newnesi (Pisces, Nototheniidae) in Terra Nova Bay, Ross Sea, in relation to environmental conditions

Forty-three and 49 specimens of the Antarctic fish Trematomus newnesi were collected in the coastal waters of Terra Nova Bay, Ross Sea, during December 1994 and February 1998, respectively. The dietary composition of the two fish samples was determined by means of stomach content analysis and then compared. In general, as reported in most of the previous studies, planktivory appeared to be the main feeding habit of T. newnesi. However, the different environmental conditions occurring in the study area in the two periods investigated, such as the degree of the sea-ice coverage and the related amount of light available below the ice, influenced the food composition of T. newnesi. In December 1994, the whole area investigated was covered by a thick layer of sea ice and the diet of T. newnesi consisted of few prey taxa. Some species that characterize the so-called “cryopelagic habitat”, such as the euphausiid Euphausia crystallorophias and the copepod Metridia gerlachei, were by far the most important prey, followed by amphipods and the pteropod Limacina helicina. Conversely, the ostracod Alacia belgicae and larval stages of fish (Pleuragramma antarcticum) were consumed occasionally. In late summer (February 1998), the lack of sea-ice coverage and changes in the associated fauna influenced the feeding habit of T. newnesi. In this period the food spectrum appeared to be more diverse, revealing an active feeding search in the water column. The bulk of food was composed of several prey groups, such as E. crystallorophias, hyperiid amphipods (Hyperiella dilatata), copepods, L. helicina and several species of fish larvae. Present data provide evidence of a marked feeding plasticity of T. newnesi, in response to diverse environmental conditions that characterize the High-Antarctic Zone. Accepted: 17 July 1999     

Notes on the field behaviour of two ant speciesMyrmecia desertorum Wheeler andMyrmecia dispar (Clark) (Hymenoptera: Formicidæ)

The behaviour ofMyrmecia desertorum Wheeler andMyrmecia dispar (Clark) was studied in the field at intervals during winter and summer from 1963 to 1967. The daily and seasonal pattern and type of activity of the species differed considerably. In winter, the workers foraged in the late morning and afternoon, while in summer they foraged in the early morning and late afternoon. Both species foraged largely on nearby trees. Most of the worker population in twoM. dispar nests left to forage. The diet of both species was very dissimilar in summer when the workers foraged in large numbers.Field observations on orientation suggest that the workers memorize the position of trees on which to forage and that visual stimuli are important for capturing prey. Migration to new abodes by two colonies ofM. desertorum and transportation of workers are described.     

Anthropogenic radionuclides bioaccumulation in Antarctic marine fauna and its ecological relevance

The paucity of investigations on the presence of artificial radionuclides and their bioaccumulation in Antarctic fauna is due to the erroneous belief that this area is pristine. We report evidence that significant levels of the artificial radionuclides Sr-90, Cs-137, Am-241 and plutonium isotopes can be found in sponges, bivalves, krill and demersal fish fauna of Terra Nova Bay (Ross Sea), sometimes with a seasonal pattern. Increasing concentrations of Cs-137 were detected in the bivalve Adamussium colbecki (Antarctic scallop) during austral summer months, as a result of major trophic activity and changes in metabolic rates. Bioconcentration factors for artificial radionuclides in different Antarctic species are presented and discussed in relation to their different trophic strategies. Unexpectedly high radiocesium bioconcentration factors determined in bivalves suggested the particular role played by filter feeding in bioaccumulation, particularly in summer when radionuclide bioavailability is enhanced. The feeding preference of the trematomiid fish Trematomus bernacchii for the scallop A. colbecki is confirmed, not only by fish gut content analyses, but also through radiometric results. Transuranics bioaccumulation by sensitive species allowed some interesting comparisons on the different plutonium contamination of the southern hemisphere with respect to the northern one. Accepted: 25 April 2000     

Microhabitat selection and feeding relations of smooth and warty newts, Triturus vulgaris and T. cristatus, at an upland pond in mid-Wales

The utilization of microhabitat and food resources by Triturus vulgaris and T. cristatus was studied in an upland pond in mid-Wales. From April to June T. vulgaris was more evenly distributed across the pond than T. cristatus , which showed a preference for the middle of the pond and the bottom of the water column. From July to September however, when most T. vulgaris had left the pond, T cristatus was evenly distributed within the water column and a much higher proportion was captured around the shorelines. Both species appear to be generalist predators with diets limited by prey size. Zooplankton were the most important prey for T. vulgaris , while leeches formed the bulk of the diet of T. cristatus . However, T. cristatus did not select larger-sized zooplankton than T. vulgaris . Large body size therefore enables T. cristatus to consume a wider range of prey sizes than T. vulgaris . Microhabitat niche overlap was greater than feeding niche overlap between the species.     

Metabolic rate and food availability of the Antarctic amphipod <Emphasis Type="Italic">Gondogeneia antarctica</Emphasis> (Chevreux 1906): seasonal variation in allometric scaling and temperature dependence

Among the few existing works on seasonal variation in metabolic rate of polar species, most have been conducted during summer due to logistic constraints and have been focused on species that cease feeding during winter. In this work, we present the first extensive data set on the seasonal variation in metabolic rate of G. antarctica, an abundant amphipod that feeds throughout the year, and its relationship with body size, potential food availability and temperature. We measured the resting metabolic rate (RMR) of groups of individuals during 6 months from late summer through winter at 4 experimental temperatures and for a wide range of body size. RMR had a negative allometric scaling with body size and showed a tendency to increase with temperature as expected. However, temperature and body size effects on RMR showed a significant temporal variation, and an increase in temperature decreased scaling exponents. RMR at the mean seawater temperature throughout the study showed a strong seasonal variation following food availability: RMR decreased from the end of summer through winter, coinciding with a reduction in microphytobenthos stock, but recovered summer values in August, when an epontic algae boom occurred. The seasonal factorial aerobic scope (×2.37) is lower than benthic Antarctic invertebrates that cease feeding during winter, in agreement with what is expected based on theoretical grounds. Results suggest that seasonal variation of RMR would allow G. antarctica to achieve a high efficiency in energy utilization, while maintaining the ability to exploit sudden changes in food supply.     

Geographic variation in resource use by specialist versus generalist butterflyfishes

Localised patterns of resource use can be constrained by multiple factors. Comparison of resource use at multiple locations with differing resource availability can allow fundamental specialists to be distinguished from species that simply feed predominantly on prey types that are locally abundant. This study investigates geographic variation in the feeding ecology of coral‐feeding butterflyfishes to examine whether patterns of resource use and levels of dietary specialisation vary among distinct locations, corresponding with changes in resource availability. Our specific aims were to investigate whether the dietary niche breadth of four butterflyfishes varies among five geographically separated locations and assess whether each species utilises similar resources in each location. Resource availability and dietary composition of four butterflyfishes were quantified at three sites across each of five geographic locations throughout the Pacific. Niche breadth, niche overlap, and resource selection functions were calculated for each species at each site and compared among locations. Availability of dietary resources varied significantly among locations and sites. Chaetodon vagabundus, C. citrinellus and C. lunulatus had low levels of dietary specialisation and used different resources in each location. Chaetodon trifascialis had high levels of dietary specialisation and used the same few resources in each location. Our results indicate that relative levels of dietary specialisation among different butterflyfishes do hold at larger spatial scales, however, geographical variation in the dietary composition of all butterflyfishes indicates that prey availability has a fundamental influence on dietary composition. Highly specialised species such as C. trifascialis will be highly vulnerable to coral loss as they appear to be largely inflexible in their dietary composition. However, the increased feeding plasticity observed here for C. trifascialis suggests this species may have a greater capacity to respond to coral loss than previously assumed.     

Induction of mixed function oxidase (MFO) system in two species of antarctic fish from Terra Nova Bay (Ross Sea)

Summary The aim of this study was to investigate the detoxicant Mixed Function Oxidase system in two species of Antarctic fish, C. hamatus and P. bernacchii, collected during the Antarctic summer of 1989–1990 at the Italian Scientific Station at Terra Nova Bay (Ross Sea). Several specimens were induced by injection of phenobarbital (PB), 3-methylcholanthrene (3-MC) and PCBs in the caudal vein. The results show significant differences between the two species. In C. hamatus, basal activity of benzo(a)pyrene monooxygenase (BPMO) was among the lowest measured even in fish of temperate seas, and in P. bernacchii it was 20 times lower. The values of regenerating activities (NADPH-cytochrome c reductase (NADPH-CYTCRED), NADH-cytochrome c reductase (NADH-CYTCRED) and NADH-ferricyanide reductase (NADH-FERRIRED) suggest that the two species use different electron donor molecules. Injection of chemicals in the caudal vein did not provoke induction of MFO activity in P. bernacchii. In C. hamatus, phenobarbital and PB-type inducers did not cause induction but there was a statistically significant response to 3-MC.     

Predator–prey interactions: why do larger albatrosses eat bigger squid?

The relationship between predator sizes and prey sizes is well documented for terrestrial but rarely for marine ecosystems. We show that wandering albatrosses, the biggest albatross species, feed on larger cephalopod prey than those consumed by smaller albatrosses (grey-headed and black-browed albatrosses). This reflects differences in timing of breeding, foraging ecology and their feeding methods. Wandering albatrosses breed later in the year, during the austral winter, than smaller albatrosses (therefore catching older squid) and forage most of the year in Antarctic open waters, sub-Antarctic, subtropical and tropical waters, overlapping minimally with the smaller albatrosses' foraging range while breeding. Also, wandering albatrosses mostly scavenge whereas smaller albatrosses feed more on live prey. Prey ecology may also play a key role because many squid species might experience post-spawning mortality during the austral winter, becoming easily available to wandering albatrosses. Spawning in winter can be linked to predator avoidance (i.e. reduction in mortality in winter by avoiding pelagic predators) and would allow squid larvae to develop and take advantage of the high productivity (i.e. Antarctic phytoplankton bloom) in spring and at the beginning of summer. Thus, aspects of prey and predator ecology may combine to generate observed differences in prey size.     

A summer-winter comparison of zooplankton in the oceanic area Around South Georgia

Summary Zooplankton was sampled with RMT (1+8) gear on a synoptic grid of stations centred on South Georgia during the austral summer (November/December 1981) and winter (July/August 1983). This initial paper compares zooplankton biomass, vertical distribution and species composition from RMT 1 catches in the oceanic portion of the grid (water depth greater than 2000 m) during the two surveys. In the winter survey, mean zooplankton biomass within the top 1000 m of the water column was 68% of its summer level. This drop was largely due to a decrease in abundance of krill (Euphausia superba), although biomass of copepods and remaining zooplankton also decreased. Copepods averaged 48% of total biomass in summer and winter, but outnumbered all other taxa put together by a factor of 10. Antarctic epipelagic species predominated around the island in the summer survey but tended to be replaced by sub-Antarctic or cosmopolitan species during the winter survey. The majority of zooplankton also showed a downwards seasonal migration out of the top 250 m layer in winter. However, several epipelagic species, including E. superba, did not migrate, and these tended to have the largest summer-winter differences in overall abundance. These trends were attributed to variation in the position of the Polar Front, which lay north of the island during the summer survey but lay across the survey area in winter, resulting in a greater influence of sub-Antarctic water and the displacement of Antarctic species.     

Important marine habitat off east Antarctica revealed by two decades of multi‐species predator tracking

Satellite telemetry data are a key source of animal distribution information for marine ecosystem management and conservation activities. We used two decades of telemetry data from the East Antarctic sector of the Southern Ocean. Habitat utilization models for the spring/summer period were developed for six highly abundant, wide‐ranging meso‐ and top‐predator species: Adélie Pygoscelis adeliae and emperor Aptenodytes forsteri penguins, light‐mantled albatross Phoebetria palpebrata, Antarctic fur seals Arctocephalus gazella, southern elephant seals Mirounga leonina, and Weddell seals Leptonychotes weddellii. The regional predictions from these models were combined to identify areas utilized by multiple species, and therefore likely to be of particular ecological significance. These areas were distributed across the longitudinal breadth of the East Antarctic sector, and were characterized by proximity to breeding colonies, both on the Antarctic continent and on subantarctic islands to the north, and by sea‐ice dynamics, particularly locations of winter polynyas. These areas of important habitat were also congruent with many of the areas reported to be showing the strongest regional trends in sea ice seasonality. The results emphasize the importance of on‐shore and sea‐ice processes to Antarctic marine ecosystems. Our study provides ocean‐basin‐scale predictions of predator habitat utilization, an assessment of contemporary habitat use against which future changes can be assessed, and is of direct relevance to current conservation planning and spatial management efforts.     

Winter ecology of Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) and brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) in a subarctic lake,Norway

We studied habitat choice, diet, food consumption and somatic growth of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) during the ice-covered winter period of a subarctic lake in northern Norway. Both Arctic charr and brown trout predominantly used the littoral zone during winter time. Despite very cold winter conditions (water temperature <1°C) and poor light conditions, both fish species fed continuously during the ice-covered period, although at a much lower rate than during the summer season. No somatic growth could be detected during the ice-covered winter period and the condition factor of both species significantly declined, suggesting that the winter feeding rates were similar to or below the maintenance requirements. Also, the species richness and diversity of ingested prey largely decreased from summer to winter for both fish species. The winter diet of Arctic charr <20 cm was dominated by benthic insect larvae, chironomids in particular, and Gammarus lacustris, but zooplankton was also important in December. G. lacustris was the dominant prey of charr >20 cm. The winter diet of brown trout <20 cm was dominated by insect larvae, whereas large-sized trout mainly was piscivorous, feeding on juvenile Arctic charr. Piscivorous feeding behaviour of trout was in contrast rarely seen during the summer months when their encounter with potential fish prey was rare as the small-sized charr mainly inhabited the profundal. The study demonstrated large differences in the ecology and interactions of Arctic charr and brown trout between the winter and summer seasons.     

Antarctic teleost immunoglobulins: more extreme, more interesting

We have investigated the immunoglobulin molecule and the genes encoding it in teleosts living in the Antarctic seas at the constant temperature of −1.86 °C. The majority of Antarctic teleosts belong to the suborder Notothenioidei (Perciformes), which includes only a few non-Antarctic species. Twenty-one Antarctic and two non-Antarctic Notothenioid species were included in our studies. We sequenced immunoglobulin light chains in two species and μ heavy chains, partially or totally, in twenty species. In the case of heavy chain, genomic DNA and the cDNA encoding the secreted and the membrane form were analyzed. From one species, Trematomus bernacchii, a spleen cDNA library was constructed to evaluate the diversity of VH gene segments. T. bernacchii IgM, purified from the serum and bile, was characterized. Homology Modelling and Molecular Dynamics were used to determine the molecular structure of T. bernacchii and Chionodraco hamatus immunoglobulin domains. This paper sums up the previous results and broadens them with the addition of unpublished data.     

WINTER FEEDING INTENSITY OF NARWHALS (MONODON MONOCEROS)

Stomach contents from 121 narwhals ( Monondon monoceros ) harvested in the eastern Canadian High Arctic and West Greenland were used to quantify seasonal changes in feeding activity and prey selection. Stomachs collected from summer harvests were mostly empty with little evidence of recent feeding. Stomachs collected in late fall and winter harvests had considerable amounts of undigested material with evidence of recent feeding. In summer, Arctic cod ( Arctogadus glacialis ), polar cod ( Boreogadus saida ), and Gonatus squid spp. constituted the narwhal diet. In fall, Gonatus fabricii was the only prey item observed. In late fall and winter, Greenland halibut ( Reinhardtius hippoglossoides ) and G. fabricii were the dominant prey items, observed in 51% and 73% of stomachs collected, respectively. Greenland halibut taken by narwhals were on average 39 cm (SD 8) and 556 g (306) and G. fabricii were on average 23 g (15) with mean mantle lengths of 85 mm (24). The low diversiry of prey species indicates narwhals have a restricted diet across all seasons. This study presents the first information on the winter diet of the narwhal and suggests Baffin Bay and Davis Strait are heavily utilized for feeding, in contrast to limited food intake during the summer period.