Antarctic Silverfish Pleuragramma Antarcticum Research Articles

Born among the ice: first morphological observations on two developmental stages of the Antarctic silverfish Pleuragramma antarcticum, a key species of the Southern Ocean

The Antarctic silverfish Pleuragramma antarcticum is a keystone species in the Southern Ocean ecosystem, providing one of the major links between lower and higher trophic levels. Despite the importance of this species, surprisingly little is known of its early development. The first spawning area for the silverfish has been recently identified in the near-shore of Terra Nova Bay (Ross Sea). Evidence indicates that spawning and embryo development occurs in the cryopelagic environment, below the seasonal pack-ice. In order to contribute to the knowledge of the life cycle of this very important Antarctic species, we carried out the first histological characterization on pre-hatching embryos and newly hatched larvae. Embryonated eggs and larvae of P. antarcticum were collected between late October and November 2005 at TNB through holes drilled into the sea ice. Embryonic stage just before hatching and the first post-hatching stage were the most abundant within our samples and thus were analysed using both macroscopic and histological approaches. Early life stages of the Antarctic silverfish revealed interesting features: the sensory system, foraging apparatus and heart appeared well developed, whereas the liver and gills were underdeveloped. Morphological details of the organogenesis were performed, providing the first substantial information on the development of P. antarcticum and representing a further steps towards the knowledge of the life cycle of this important Antarctic key species.

Born among the ice: first morphological observations on two developmental stages of the Antarctic silverfish Pleuragramma antarcticum, a key species of the Southern Ocean

Born among the ice: first morphological observations on two developmental stages of the Antarctic silverfish Pleuragramma antarcticum, a key species of the Southern Ocean

Distribution, abundance and ecological relevance of pelagic fishes in the Lazarev Sea, Southern Ocean

The distribution and abundance of larval and postlarval fishes was investigated in the Lazarev Sea, Southern Ocean, in March and April 2004. The upper 200 m of the water column were sampled with an 8 m 2 rectangular midwater trawl at 93 stations. The larval species community clus- tered in a diverse coastal community with high densities of Antarctic silverfish Pleuragramma antarcticum larvae and a less diverse offshore community dominated by Antarctic jonasfish Notolepis coatsi and the lanternfish Electrona antarctica. No postlarval fish were caught in coastal areas. The offshore community of postlarval fishes consisted of the deep-sea smelt Bathylagus antarcticus, and the lanternfishes Gymnoscopelus braueri, G. nicholsi and E. antarctica. The latter species clearly dominated, occurring at mean individual and wet mass densities of 0.17 individuals m -2 and 0.26 g m -2 , respectively. A generalized additive model significantly related the density of postlarval E. antarctica to the abundance of Antarctic krill Euphausia superba, ocean depth and sea surface tem- perature. The diet of E. antarctica was dominated by copepods and euphausiid larvae. Mean energy density of E. antarctica in the upper 200 m was 2.8 kJ m -2 , which is equivalent to 36% of the energy stored in Antarctic krill stocks and probably would be considerably higher if a greater depth range were considered. This suggests that E. antarctica is a major energy transmitter in the food web of the Lazarev Sea, challenging the classical krill-dominated food web paradigm of the Southern Ocean.

State-dependent energy allocation in the pelagic Antarctic silverfish Pleuragramma antarcticum: trade-off between winter reserves and buoyancy

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 326:269-282 (2006) - doi:10.3354/meps326269 State-dependent energy allocation in the pelagic Antarctic silverfish Pleuragramma antarcticum: trade-off between winter reserves and buoyancy Joachim Maes1,3,*, Anton Van de Putte1, Jean-Henri Hecq2, Filip A. M. Volckaert1 1Katholieke Universiteit Leuven, Laboratory of Aquatic Ecology, Ch. Debériotstraat 32, 3000 Leuven, Belgium 2Université de Liège, Departement Océanologie, Bât. B6 Océanologie, Allée de la Chimie 3, 4000 Liège, Belgium 3Present address: Flemish Institute for Technological Research (VITO), Boeretang 2000, 2400 Mol, Belgium *Email: joachim.maes@vito.be ABSTRACT: Icefishes of the perciform suborder Notothenioidei dominate the Antarctic ichthyofauna. These species originated from a benthic ancestor and do not possess a swimbladder. However, some notothenioids have achieved neutral buoyancy through skeletal reductions as well as storage of lipids to reduce body mass relative to seawater. These adaptations enable them to exploit the highly productive pelagic realm. Mobilizing these lipid reserves in periods of critically low food intake may lead to buoyancy problems. Accumulating and conserving these reserves may slow down the development of somatic and reproductive tissues and hence future reproductive output. We constructed a dynamic state variable model to investigate how ingested energy is partitioned over 3 state variables: lipid reserves, structural protein body mass and egg development. Two forms of the model differed in that lipid reserves were either included in or excluded from the total metabolic energy budget of an individual. The model was parameterised for the Antarctic silverfish Pleuragramma antarcticum, a key species in the pelagic food web of the high Antarctic zone of the Southern Ocean. In Pleuragramma, lipids are stored in unique extracellular lipid sacs, which are thought to serve as buoyancy aids and energy reserves. The model predicts optimal habitat selection and an optimal energy allocation strategy by maximizing future reproductive output. The environment is simulated using vertical gradients in water temperature, optical properties, food availability and predation risk. The form of the model that considers lipids as metabolically inactive reserves best replicates field measurements of fat content and yields high values for fitness in Pleuragramma. Uncoupling fat reserves from metabolism, through the development of extracellular lipid sacs, probably represents a key adaptation in the evolution towards a pelagic lifestyle in a fish species with a low scope for activity. KEY WORDS: Antarctica · Dynamic state variable model · Lipid metabolism · Pelagic fish · Notothenioidei · Southern Ocean Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 326. Online publication date: November 17, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Demographic history and population structure of the Antarctic silverfish Pleuragramma antarcticum

The Antarctic silverfish Pleuragramma antarcticum (Nototheniidae) is the most abundant pelagic fish inhabiting Antarctic waters. In this study we investigated, through partial sequencing of the D-loop mitochondrial region, samples collected at four different locations in the Southern Ocean, three in the Atlantic and one in the Pacific sector. Sampling was replicated in two different years at two locations. Sequence analysis showed a remarkably high polymorphism, with 110 haplotypes over the 256 investigated specimens, and about 80% of haplotypes occurring only once. Neutrality tests indicated that all samples were not at mutation-drift equilibrium, and suggested a past population expansion. This result was supported by the presence of a star-like topology in the D-loop gene tree, and by results of mismatch distribution. The start of the expansion was dated, using a specifically calibrated clock, between 111 and 126 thousand years ago. This value corresponds to the start of the cooling period that led to the last glaciation peak, and is in close agreement with a recently suggested range expansion for pelagic Antarctic ecosystems. Analysis of molecular variation indicated a small, though highly significant, value of differentiation between samples. This result, together with the lack of association between clades and geographical locations, indicates a weak population structure for the species.

Antioxidant efficiency in early life stages of the Antarctic silverfish, Pleuragramma antarcticum: Responsiveness to pro-oxidant conditions of platelet ice and chemical exposure

The Antarctic silverfish Pleuragramma antarcticum is a key organism in the ecology of Southern Ocean. Eggs with fully developed yolk-sac embryos and newly hatched larvae have been recently observed to occur in the platelet ice accumulating below the sea-ice layer. This environment has strong pro-oxidant characteristics at the beginning of austral spring, when the rapid growth of algal ice communities, the massive release of nutrients and the photoactivation of dissolved organic carbon and nitrates, all represent important sources for oxyradical formation. Such processes are concentrated in a short period of a few weeks which overlaps with the final development of P. antarcticum in platelet ice. The aim of this work was to characterize the antioxidant system in embryos of P. antarcticum and the responsiveness toward the natural increase of pro-oxidant conditions in early spring. Considering the lack of ecotoxicological data on this species and its pivotal importance in the ecosystem of Southern Ocean, the sensitivity of its early life stages was also evaluated after laboratory exposures to environmentally relevant doses of benzo(a)pyrene, as a model chemical potentially released from anthropogenic activities. Obtained results revealed a marked temporal increase of antioxidants in embryos of P. antarcticum as adaptive counteracting responses to oxidative conditions of platelet ice. Particularly prompt responses were observed for glutathione metabolism which, however, did not prevent formation of increasing levels of lipid peroxidation products; from the analysis of total oxyradical scavenging capacity (TOSC), the overall efficiency to neutralize peroxyl radicals remained almost constant while slightly lower TOSC values were obtained toward hydroxyl radicals at the end of sampling period. Laboratory exposures to 0.5–5 μg/l BaP caused a significant accumulation of this PAH but no significant effects on the activity of cytochrome P450. Antioxidants of exposed embryos showed less marked variations than embryos in field conditions suggesting that the elevated pro-oxidant challenge, to which these organisms are naturally adapted, might be responsible for the moderate responsiveness to pro-oxidant chemicals.

Classification of Weddell seal dives based on 3-dimensional movements and video-recorded observations

We classified Weddell seal Leptonychotes weddellii dives based on 58 spatial and tempo- ral variables derived from 3-dimensional movements and assigned functions to the dive classifications based on video-recorded behavior. The variables were measured or calculated from data obtained by attaching a video and data recorder to the backs of 10 adult Weddell seals diving from an isolated ice hole in McMurdo Sound, Antarctica. Our analysis revealed 4 types of dives. Type 1 dives were inter- mediate in duration (15.0 ± 4.2 min), deep (mean maximum depth = 378 ± 93 m) and had the steepest descent and ascent angles. Video recordings of the seals capturing prey, primarily small Antarctic silverfish Pleuragramma antarcticum, confirmed these were foraging dives. Types 2, 3 and 4 dives formed a continuum from very short, low speed, non-linear dives that were close to the hole (Type 2) to progressively longer, higher speed, very linear dives that ranged as much as 3 km from the hole (Type 4), but remained relatively shallow (<142 m) compared to Type 1 (foraging) dives. Type 2 dives were hypothesized to be related to hole-guarding behavior or the detection of other seals. Type 3 and 4 dives had characteristics suggestive of exploratory behavior. Comparisons with previously published dive classifications that were based on time-depth records showed that some functions attributed to certain dive types by previous researchers were correct, but others were not. This emphasizes the need for behavioral data for correct interpretation of dive profiles and time-depth statistics.

Food of emperor penguins ( Aptenodytes forsteri ) in the western Ross Sea, Antarctica

The diet of the emperor penguin Aptenodytes forsteri in the western Ross Sea during spring was investigated by analysis of stomach contents sampled at three different localities. At Cape Washington, emperor penguins feeding chicks consistently preyed on fishes (89 to 95% by mass) and crustaceans (5 to 11%) over the four spring seasons examined. By far the commonest prey was the Antarctic silverfish Pleuragramma antarcticum (89% of the fish prey); the remainder of fish prey were mainly unidentified juveniles of different species of channichthyid fishes. Three species dominated the crustacean part of the diet, i.e. the gammarid amphipods Abyssorchomene rossi/plebs (30% of the crustacean prey) and Eusirus microps (22%), together with the euphausiid Euphausia crystallorophias (24%). At Coulman Island and Cape Roget, fishes, mainly P. antarcticum, formed the bulk of the food (88 and 93% by mass, respectively), crustaceans were minor prey (2.5 and 0.4%), and the squid Psychroteuthis glacialis accounted for a small but significant part of the food (3.5 and 0.8%). This study emphasizes the importance of the small, shoaling pelagic fish Pleuragramma antarcticum as a key link between zooplankton and top predators, including seabirds, in the food web and marine ecosystem of the Ross Sea.

Adaptations of the Antarctic silverfish Pleuragramma antarcticum (Pisces:Nototheniidae) to pelagic life in high-Antarctic waters

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 151:205-218 (1997) - doi:10.3354/meps151205 Adaptations of the Antarctic silverfish Pleuragramma antarcticum (Pisces: Nototheniidae) to pelagic life in high-Antarctic waters Wöhrmann APA, Hagen W, Kunzmann A Most fishes in Antarctic waters belong to the suborder Notothenioidei, highly developed perciform fishes which have been able to occupy not only a variety of benthic but also pelagic niches in Antarctic waters. One of the rare truly pelagic fish species, Pleuragramma antarcticum, plays a pivotal role in high-Antarctic food webs, due to its exceptional abundance. To investigate the life history of P. antarcticum more than 16000 specimens were collected in the Weddell Sea during various cruises with RV 'Polarstern'. Apart from the more general life cycle adaptations with respect to reproduction, migrations, and feeding behaviour, P. antarcticum has developed a number of specific biochemical and physiological adaptations to cope with the environmental conditions in these permanently cold and highly seasonal Antarctic waters. During its second summer P. antarcticum starts to accumulate large lipid deposits, mainly in the form of triacylglycerols. These low-density compounds provide the species with hydrostatic lift, an important factor for a pelagic fish without a swim bladder. The lipid stores may also serve as energy reserves. Highly polar brain gangliosides suggest wide-ranging neurophysiological adaptations to ensure proper functioning of the nervous system in icy waters. To avoid freezing in the presence of frazil ice P. antarcticum contains efficient antifreeze glycoproteins. A newly discovered glycoprotein acts as an additional antifreeze agent. Although pelagic, adult P. antarcticum are rather sluggish, which is indicated by the small total gill area as well as blood physiological characteristics. Such behaviour diminishes routine energy costs. Blood viscosity is reduced and at least 2 major haemoglobins are found. Provided that these haemoglobins are functionally different, they indicate a strong relationship between physiological and biochemical adaptations of the oxygen transport system and life style. P. antarcticum represents a prime example of the complexity of adaptations necessary to thrive in the pelagic realm of Antarctic shelf waters, a niche largely unoccupied by other fish species. High-Antarctic · Notothenioid fish · Pleuragramma antarcticum · Life history · Energetics · Lipids · Gangliosides · Antifreeze glycoproteins · Gill · Haemoglobins Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 151. Publication date: May 22, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Food and feeding ecology of emperor penguins in the eastern Weddell Sea

The diet of the emperor penguin Aptenodytes forsteri in the eastern Weddell Sea, Antarctica was studied during October and November 1986 by stomach content analysis. Emperor penguins fed mainly on Antarctic krill Euphausia superba, Antarctic silverfish Pleuragramma antarcticum and squid Psychroteuthis glacialis. Benthic prey was not found. The prey composition suggests two different feeding strategies, shallow dives exploring the rugged underside of sea ice where krill is taken, and deep dives when mesopelagic fish and squid are consumed. Chicks were fed on average every 1.44 days.

Age and growth of Antarctic Silverfish Pleuragramma antarcticum Boulenger, 1902, from the southern Weddell Sea and Antarctic Peninsula

The length and age (determined from sagittal otoliths) of 1787 Antarctic Silverfish (Pleuragramma antarcticum) was analyzed from west of the Antarctic Peninsula (63°S/64°W) and southern Weddell Sea (73°S–77°S). Otolith diameter (D) was related to standard length by $$D (mm) = 0.011 x SL^{1.034} (mm).$$ Otolith diameters were between 0.1 mm (postlarvae) and 3.0 mm. The calculated growth from otolith readings indicated annual length increments of approximately 20 to 10 mm for fish from 2 to 12 years old. This low, but relatively constant growth is reflected in the Von Bertalanffy Growth Formula (VBGF) as $$L_t = 308 (1 - e^{ - 0.0715 (t + 1.15)} ) (mm).$$ Fish in the size range known from the Weddell Sea of 34 to 245 mm standard length are thus 1 to 21 years old. Growth Performance “P” of 1.1 is at the lower limit of values observed in Antarctic fish. In spite of low “k”, Pleuragramma antarcticum does not grow to large size. This finding is discussed in the light of adaptive demands of the species as a planktivorous pelagic nototheniid in the Antarctic.

Stomach contents of the Antarctic Silverfish Pleuragramma antarcticum from the southern and eastern Weddell Sea (Antarctica)

The stomach contents of 142 Pleuragramma antarcticum from the southernmost part of the Weddell Sea (Gould Bay: 77°19′S) and from the eastern coast (72°–74°S) were analyzed. The fish were collected in February 1983 and stored frozen. Size range of the investigated specimens was from 6.4 cm SL (7.3 cm TL) to 21.9 cm SL (24.1 cm TL). The fish were caught by bottom trawl (Gould Bay) and Agassiz Trawl and pelagic RMT-m net in the upper 300 m layer at the eastern coast, respectively. Thirty-six stomachs were empty or contained sand only. The most important prey in terms of biomass were euphausiids, which occurred in 49 stomachs at a mean number of 2. Their dry weight was estimated to be 15–50 times that of the next important food items, which were copepods, gastropods and gammarids. Krill (Euphausia superba) constituted up to 14% of the euphausiids in the diet of fish caught in the eastern Weddell Sea. The rest was usually made up by Euphausia crystallorophias. This species was taken with preference even when the abundance of E. superba in accompanying plankton catches was 16 times higher. In the Gould Bay, gastropods were frequently eaten despite high numbers of copepods in the plankton, whereas in the eastern Weddell Sea, copepods were abundant both in plankton and in the stomach content. The almost complete absence of the early stages of fish in the diet of Pleuragramma antarcticum in the southern and eastern Weddell Sea is due to a pronounced vertical segregation of fish of different sizes. This distribution pattern is thought to be an adaptive mechanism to avoid intraspecific predation, as 90% of the ichthyoplankton in that area is Pleuragramma antarcticum.