Euphausia Crystallorophias Research Articles

Trophic interactions of micro- and mesozooplankton in the Amundsen Sea polynya and adjacent sea ice zone during austral late summer

To elucidate the trophic link between micro- and mesozooplankton in the Amundsen Sea polynya (ASP) and adjacent sea ice zone, we estimated the impact of microzooplankton grazing on major phytoplankton groups, as well as the diet composition, ingestion rate, and prey selectivity of two copepods and Euphausia crystallorophias larvae on microbial communities during the late summer. Phaeocystis antarctica, which was ingested by micro- and mesozooplankton, comprised most phytoplankton biomass. Herbivorous microzooplankton consumed at least half of the phytoplankton production, but the microzooplankton grazing may not contribute strongly to the decline of the phytoplankton bloom. Three mesozooplankton species (Calanoides acutus, Metridia gerlachei, and E. crystallorophias larvae) preferentially grazed on ciliates and heterotrophic dinoflagellates (HDF) with sizes from 20 to >100 µm over phytoplankton. Although microzooplankton comprised only an average of 41.7 ± 3.2% o the total carbon available in the natural prey pool, they accounted for an average of 75.4 ± 2.9% of total carbon ingested by copepods and krill larvae. Heterotrophic food sources made up a substantial proportion of mesozooplankton diets, with strong positive selection for microzooplankton at most locations regardless of phytoplankton size and type. In particular, HDF comprised the major dietary component of mesozooplankton in the study area. The presence of mesozooplankton reduced the grazing pressure on P. antarctica and diatoms through predation on herbivorous microzooplankton. Approximately half of the primary production capacity may have indirectly reached mesozooplankton through microzooplankton consumption. Thus, strongly selective feeding behavior and higher grazing pressure on microzooplankton indicated the importance of microheterotrophic pathways through strong trophic coupling between mesozooplankton and the microbial food web during the decline of phytoplankton bloom. In the highly productive ASP system, food web structure can be classified as multivorous, whereby herbivorous and omnivorous modes both play significant roles in carbon export, enhancing the efficiency of the pelagic food web.

Post-fledging survival of Adélie penguins at multiple colonies: chicks raised on fish do well

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 601:239-251 (2018) - DOI: https://doi.org/10.3354/meps12687 Post-fledging survival of Adélie penguins at multiple colonies: chicks raised on fish do well David G. Ainley1,*, Katie M. Dugger2, Mario La Mesa3, Grant Ballard4, Kerry J. Barton5, Scott Jennings2,4,6, Brian J. Karl5, Amelie Lescroël4, Phil O’B. Lyver5, Annie Schmidt4, Peter Wilson5 1H. T. Harvey & Associates Ecological Consultants, Los Gatos, CA 95032, USA 2US Geological Survey, Oregon Cooperative Fish and Wildlife Research Unit, Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 97331, USA 3ISMAR-CNR, Istituto di Scienze Marine, UOS di Ancona, 60125 Ancona, Italy 4Point Blue Conservation Science, Petaluma, CA 94954, USA 5Landcare Research, Lincoln 7640, New Zealand 6Present address: ACR, Cypress Grove Research Center, Marshall, CA 94940, USA *Corresponding author: dainley@penguinscience.com ABSTRACT: We assessed whether the mass of Adélie penguin Pygoscelis adeliae fledglings at 3 colonies of markedly disparate size on Ross Island, Ross Sea, correlated with their eventual return as subadults. We compared our results with those from Anvers Island, Bellingshausen Sea. Colony sizes at Ross Island have been increasing, contrary to decreasing size at Anvers Island. At Ross Island, during the month prior to fledging, chick diet consisted equally of energy-dense Antarctic silverfish Pleuragramma antarctica and less-caloric crystal krill Euphausia crystallorophias, while at Anvers Island the diet was principally Antarctic krill E. superba. At Ross Island, the mass of fledglings who subsequently returned (mean ± SE: 3.4 ± 0.0411 kg) exceeded that of those not seen again (3.2 ± 0.0251 kg), compared to Anvers Island (3.2 vs. 3.0 kg, respectively). At Ross Island, fledging mass was inversely related to colony size and, at the largest colony, fledging mass decreased as the colony grew. Average mass of returnees at the largest colony was less than the mass at Anvers Island for those fledglings that did not return. The mean proportion of fish in the chicks’ diet decreased at the largest Ross Island colony over time, as did fledging mass. We hypothesize that intraspecific competition increased along with colony size, decreasing the availability of fish. We further hypothesize that at the large Ross Island colony, post-fledging penguins must be finding adequate prey, and more energy-dense fish, just outside the colony’s foraging area to explain opposing trends in colony trajectories. KEY WORDS: Adélie penguin · Antarctic silverfish · Anvers Island · Central-place foraging · Ross Island · Intraspecific trophic competition Full text in pdf format PreviousNextCite this article as: Ainley DG, Dugger KM, La Mesa M, Ballard G and others (2018) Post-fledging survival of Adélie penguins at multiple colonies: chicks raised on fish do well. Mar Ecol Prog Ser 601:239-251. https://doi.org/10.3354/meps12687 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 601. Online publication date: August 09, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Distribution and abundance of mesozooplankton in the Ross Sea, Antarctica

Zooplankton (meso- and macrozooplankton) distributions and biomass are poorly known in the Ross Sea despite their importance in energy transfer within food webs and biogeochemical cycles. Mesozooplankton abundance and biomass on the continental shelf are spatially variable and span two orders of magnitude during austral summer. Selected sub-regions (near the shelf break or ice shelf) show similar variability, suggesting that other processes, either oceanographic or biological, influence zooplankton on smaller scales. Biomass at one location (76.5° S, 172° E) was consistently elevated throughout January, although the causes of this “hotspot” were unclear. At a station near the ice shelf, abundance and biomass of the pteropod Limacina antarctica was very high. Zooplankton biomass at this location was sevenfold greater than any other station, and while the high biomass was driven by pteropod contributions, copepods were also abundant. Copepods dominated the mesozooplankton composition at all other stations, comprising 90 and 78% on average of the total abundance and biomass. Zooplankton biomass comprised on average 3.96% of the total particulate carbon (0–200 m) and was weakly correlated with chlorophyll and biogenic silica. We suggest that summer zooplankton growth and biomass, while linked to organic matter concentrations, are regulated by other factors (e.g., predation by crystal krill and Antarctic silverfish), as both grazers may be responsible for significant losses. Our data indicate that, contrary to other suggestions, summer zooplankton biomass and abundance in the Ross Sea are similar to those in other Antarctic coastal regions.

Krill distribution in relation to environmental parameters in mesoscale structures in the Ross Sea

Krill, a key pelagic resource of the Antarctic food web, provides an important link between primary and secondary plankton production and top predators. Since krill abundance is a crucial factor in Antarctic ecosystem functioning, its monitoring supplies vital data. Acoustic surveys are an effective approach to estimating krill abundance. An acoustic survey was conducted in the western Ross Sea in January 2014–10years after a similar survey by our team - to estimate krill abundance and biomass and monitor oceanographic conditions. Antarctic krill (Euphausia superba) was detected in the northern part of the western Ross Sea and dense swarms of ice krill (Euphausia crystallorophias) were found in its central coastal area. Data analysis revealed an inverse correlation between E. superba density and salinity in the water column, whereas a positive correlation was found between E. crystallorophias abundance and fluorescence; the latter relationship was confirmed in thematic maps of E. crystallorophias spatial distribution and fluorescence. Comparison of 2004 and 2014 biomass data showed a much greater abundance of both species in the more recent survey.

Horizontal niche partitioning of humpback and fin whales around the West Antarctic Peninsula: evidence from a concurrent whale and krill survey

A dedicated aerial cetacean survey was conducted concurrently to a standardised net trawl survey for krill in order to investigate distribution patterns of large whales and different krill species and to investigate relationships of these. Distance sampling data were used to produce density surface models for humpback (Megaptera novaeangliae) and fin whales (Balaenoptera physalus) around the West Antarctic Peninsula (WAP). Abundance for both species was estimated over two strata in the Bransfield Strait and Drake Passage. Distinct distribution patterns suggest horizontal niche partitioning of the two whale species around the WAP, with fin whales aggregating at the shelf edge of the South Shetland Islands in the Drake Passage and humpback whales in the Bransfield Strait. Krill biomass estimated from the concurrent krill survey was used along with CTD data from the same expedition, bathymetric parameters and satellite data on chlorophyll-a and ice concentration to model krill distribution. Comparisons of the predicted distributions of both whale species with the predicted distributions of Euphausia superba, Euphausia crystallorophias and Thysanoessa macrura suggest a complex relationship rather than a straightforward correlation between krill and whales. However, results indicate that fin whales were feeding in an area dominated by T. macrura, while humpback whales were found in areas of higher E. superba biomass. Our results provide abundance estimates for humpback whales and, for the first time, fin whales in the WAP and contribute important information on feeding ecology and habitat use of these two species in the Southern Ocean.

Sex-Based Differences in Adélie Penguin (Pygoscelis adeliae) Chick Growth Rates and Diet.

Sexually size-dimorphic species must show some difference between the sexes in growth rate and/or length of growing period. Such differences in growth parameters can cause the sexes to be impacted by environmental variability in different ways, and understanding these differences allows a better understanding of patterns in productivity between individuals and populations. We investigated differences in growth rate and diet between male and female Adélie Penguin (Pygoscelis adeliae) chicks during two breeding seasons at Cape Crozier, Ross Island, Antarctica. Adélie Penguins are a slightly dimorphic species, with adult males averaging larger than adult females in mass (~11%) as well as bill (~8%) and flipper length (~3%). We measured mass and length of flipper, bill, tibiotarsus, and foot at 5-day intervals for 45 male and 40 female individually-marked chicks. Chick sex was molecularly determined from feathers. We used linear mixed effects models to estimate daily growth rate as a function of chick sex, while controlling for hatching order, brood size, year, and potential variation in breeding quality between pairs of parents. Accounting for season and hatching order, male chicks gained mass an average of 15.6 g d-1 faster than females. Similarly, growth in bill length was faster for males, and the calculated bill size difference at fledging was similar to that observed in adults. There was no evidence for sex-based differences in growth of other morphological features. Adélie diet at Ross Island is composed almost entirely of two species—one krill (Euphausia crystallorophias) and one fish (Pleuragramma antarctica), with fish having a higher caloric value. Using isotopic analyses of feather samples, we also determined that male chicks were fed a higher proportion of fish than female chicks. The related differences in provisioning and growth rates of male and female offspring provides a greater understanding of the ways in which ecological factors may impact the two sexes differently.

Fatty acid composition of Euphausia superba, Thysanoessa macrura and Euphausia crystallorophias collected from Prydz Bay, Antarctica

The information of trophic relationship is important for studying the Southern Ocean ecosystems. In this study, three dominant krill species, Euphausia superba, Thysanoessa macrura and Euphausia crystallorophias, were collected from Prydz Bay, Antarctica, during austral summer of 2009/2010. The composition of fatty acids in these species was studied. E. superba and T. macrura showed a similar fatty acid composition which was dominated by C14:0, C16:0, EPA (eicosapentenoic acid) and DHA (de-cosahexenoic acid) while E. crystallorophias showed higher contents of C18:1(n-9), C18:1(n-7), DHA and EPA than the former two. Higher fatty acid ratios of C18:1(n-9)/18:1(n-7), PUFA (polyunsaturated fatty acid)/SFA (saturated fatty acid), and 18PUFA/16PUFA indicated that E. crystallorophias should be classified as a typical omnivore with a higher trophic position compared with E. superba and T. macrura.

Modeling the transport and fate of euphausiids in the Ross Sea

Antarctic krill (Euphausia superba) and crystal krill (Euphausia crystallorophias), important components of the Ross Sea food web, differ in their population distribution. The objective of this study was to determine whether these differing distributions result primarily from differences in spawning locations, larval development times, and transport by the Ross Sea circulation. To address this objective, Lagrangian particle tracking experiments were used to simulate the transport of larvae of Antarctic krill and crystal krill. The particle simulations showed that regions providing inputs of Antarctic krill to the Ross Sea were along the outer shelf/slope. Crystal krill transport and retention were along the shallow banks on the outer Ross Sea shelf. Particles initialized in the inner shelf off Victoria Land showed high retention in the region south and along the Terra Nova Bay polynya, with timescales consistent with development times of crystal krill. These results suggest that the cyclonic circulation over the shelf contributes significantly to the dispersion and retention of crystal krill in parts of the inner Ross Sea continental shelf that overlaps with regions with high concentrations of krill-dependent top predators. The westward circulation along the shelf break contributes to the transport and aggregation of Antarctic krill in regions where Circumpolar Deep Water is observed on the outer continental shelf and along the shelf break. The transport pathways and connectivity obtained from this study provide a baseline for assessing the effects of projected changes in the Ross Sea circulation on the distribution of two important krill species.

Volume backscattering strength of ice krill (Euphausia crystallorophias) in the Amundsen Sea coastal polynya

Volume backscattering strength (Sv in dB re 1m−1) of ice krill (Euphausia crystallorophias) was observed at two frequencies (38 and 120kHz) with a calibrated split-beam echosounder system in the Amundsen Sea coastal polynya. The horizontal and vertical scattering layers in the upper 200m of the water column were known with the existence of predominant ice krill (>95%) in this region. Acoustic identification using a two-frequency dB window between Sv at 38 and Sv at 120kHz separated echoes originating from dominant ice krill from other zooplankton species. The frequency dependence of ice krill at 38 and 120kHz was examined and the result presented that ice krill might have different acoustic characteristics from other Southern Ocean zooplankton species including Euphausia superba. This result could be applied to improve the ability of acoustic identification and precise density estimation of ice krill in the high-latitude coastal waters of Antarctica.

Trophodynamics of euphausiids in the Amundsen Sea during the austral summer by fatty acid and stable isotopic signatures

The Amundsen Sea is characterized by a continental shelf, long-term sea ice, and many coastal polynyas with high biological productivity. Euphausia superba and Euphausia crystallorophias, which are dominant Antarctic krill, are major prey for most predators, such as fishes, birds, and marine mammals. An understanding of the feeding ecology of krill may provide the information for the structure and function of the Amundsen Sea ecosystem. Thus, we applied two biochemical approaches (fatty acids and stable isotopes) to determine the trophodynamics of adult krill in the Amundsen Sea. There were no significant differences in lipid contents between the two species, but the dominant storage lipids were different. Triacylglycerol (TAG) was dominant in E. superba, but wax esters (WE) were dominant in E. crystallorophias due to their different living strategies. Furthermore, the lipid content of E. crystallorophias displayed a spatial variation, being highest on the glacial edge. It was difficult to understand the feeding strategy and food source using only the fatty acid compositions of krill and in situ particulate organic matter. However, we found that specific FA ratios (18:1ω9/18:1ω7 and PUFA/SFA) and the nitrogen isotope ratio (δ15N) provide more insight into the feeding ecology of krill, such as feeding strategy and trophic position. These ratios suggest that E. crystallorophias consistently showed a higher degree of carnivorous feeding than E. superba in the Amundsen Sea during the austral summer. In conclusion, adult E. superba might more directly obtain their energy from in situ primary producers in the open sea, but, in the Amundsen Sea Polynya, adult E. crystallorophias seems to obtain their energy mainly through the microbial loop (microzooplankton). If so, E. crystallolophias would be a key player not only to transfer the energy from microbes to higher trophic levels but also to control the carbon and nitrogen cycle in the Amundsen Sea Polynya.

Diversification, evolution and sub-functionalization of 70kDa heat-shock proteins in two sister species of antarctic krill: differences in thermal habitats, responses and implications under climate change.

BackgroundA comparative thermal tolerance study was undertaken on two sister species of Euphausiids (Antarctic krills) Euphausia superba and Euphausia crystallorophias. Both are essential components of the Southern Ocean ecosystem, but occupy distinct environmental geographical locations with slightly different temperature regimes. They therefore provide a useful model system for the investigation of adaptations to thermal tolerance.Methodology/Principal FindingInitial CTmax studies showed that E. superba was slightly more thermotolerant than E. crystallorophias. Five Hsp70 mRNAs were characterized from the RNAseq data of both species and subsequent expression kinetics studies revealed notable differences in induction of each of the 5 orthologues between the two species, with E. crystallorophias reacting more rapidly than E. superba. Furthermore, analyses conducted to estimate the evolutionary rates and selection strengths acting on each gene tended to support the hypothesis that diversifying selection has contributed to the diversification of this gene family, and led to the selective relaxation on the inducible C form with its possible loss of function in the two krill species.ConclusionsThe sensitivity of the epipelagic species E. crystallorophias to temperature variations and/or its adaptation to cold is enhanced when compared with its sister species, E. superba. These results indicate that ice krill could be the first of the two species to be impacted by the warming of coastal waters of the Austral ocean in the coming years due to climate change.

Climate variability and spatiotemporal dynamics of five Southern Ocean krill species

Understanding the ecological response of marine organisms to future climate change will benefit from quantifying spatiotemporal aspects of their distribution and abundance as well as the influence of ocean–atmospheric climate modes on their population cycles. Our study provides a synthesis of 18years of data (1992–2009) for 5 krill (euphausiid) species monitored near the North Antarctic Peninsula (NAP) during austral summer. Distribution and abundance data are presented for postlarval stages of Euphausia crystallorophias, E. frigida, E. superba, E. triacantha and Thysanoessa macrura and larval E. superba and T. macrura. Intraseasonal, interannual and longer-term distribution and abundance patterns are quantified relative to climate modes driving ecosystem variability off the Antarctic Peninsula: El Niño-Southern Oscillation (ENSO), Southern Annual Mode (SAM) and associated zonal and meridional winds. Interannual abundance variations of all 5 species are significantly correlated with seasonally averaged ENSO indices and, with the exception of E. triacantha, elevated population sizes are associated with the higher productivity La Niña phase. Time-lagged responses of each species to ENSO indices approximate their generation times and suggest evolution of their life histories and reproductive efforts in accordance with the ENSO cycle. Postlarval E. crystallorophias and E. frigida and larval T. macrura demonstrate significant abundance increases after 1998 associated with a shift from an El Niño dominated period to predominantly La Niña and “Nino-neutral” conditions. Seasonal changes in species distributions and co-occurrence indicate portions of the southernmost E. frigida, E. triacantha and T. macrura populations move poleward with E. superba during late-summer, suggesting that environmental conditions associated with sea ice development (e.g., food, retention) may be more favorable than within the Antarctic Circumpolar Current during low productivity seasons. Spatial distributions of larval and postlarval T. macrura suggest 2 separate spawning populations within oceanic and coastal waters. Lastly, mean euphausiid species concentrations and abundance relationships encountered during 1992–2009 are remarkably similar to those reported for the Antarctic Peninsula during the 1928–1935 Discovery Investigations. Circumpolar observations of E. superba “superswarms” associated with a major climatically related ecosystem change in the late 1970s may have represented an episodic period of anomalous peak abundance. Subsequent abundance estimates compared to these anomalies would indicate a significant decrease, but should not be taken to reflect the impact of climate warming.

Meso- and macro-zooplankton community structure of the Amundsen Sea Polynya, Antarctica (Summer 2010–2011)

Abstract The Amundsen Sea Polynya (ASP) has, on average, the highest productivity per unit area in Antarctic waters. To investigate community structure and the role that zooplankton may play in utilizing this productivity, animals were collected at six stations inside and outside the ASP using paired “day-night” tows with a 1 m2 MOCNESS. Stations were selected according to productivity based on satellite imagery, distance from the ice edge, and depth of the water column. Depths sampled were stratified from the surface to ∼ 50–100 m above the seafloor. Macrozooplankton were also collected at four stations located in different parts of the ASP using a 2 m2 Metro Net for krill surface trawls (0–120 m). The most abundant groups of zooplankton were copepods, ostracods, and euphausiids. Zooplankton biovolume (0.001 to 1.22 ml m-3) and abundance (0.21 to 97.5 individuals m-3) varied throughout all depth levels, with a midsurface maximum trend at ∼ 60–100 m. A segregation of increasing zooplankton trophic position with depth was observed in the MOCNESS tows. In general, zooplankton abundance was low above the mixed layer depth, a result attributed to a thick layer of the unpalatable colonial haptophyte, Phaeocystis antarctica. Abundances of the ice krill, Euphausia crystallarophias, however, were highest near the edge of the ice sheet within the ASP and larvae:adult ratios correlated with temperature above a depth of 60 m. Total zooplankton abundance correlated positively with chlorophyll a above 150 m, but negative correlations observed for biovolume vs. the proportion of P. antarctica in the phytoplankton estimated from pigment ratios (19’hexanoyloxyfucoxanthin:fucoxanthin) again pointed to avoidance of P. antarctica. Quantifying zooplankton community structure, abundance, and biovolume (biomass) in this highly productive polynya helps shed light on how carbon may be transferred to higher trophic levels and to depth in a region undergoing rapid warming.

Ex situ echo sounder target strengths of ice krill Euphausia crystallorophias

Ice krill is the keystone species in the neritic ecosystem in the Southern Ocean, where it replaces the more oceanic Antarctic krill. It is essential to understand the variation of target strength (TS in dB re 1 m2) with the different body size to accurately estimate ice krill stocks. However, there is comparatively little knowledge of the acoustic backscatter of ice krill. The TS of individual, formalin-preserved, tethered ice krill was measured in a freshwater test tank at 38, 120, and 200 kHz with a calibrated split-beam echo sounder system. Mean TS was obtained from 21 individual ice krill with a broad range of body lengths (L: 13–36 mm). The length (L, mm) to wet weight (W; mg) relationship for ice krill was W=0.001218×103 × L3.53 (R2 =0.96). The mean TS-to-length relationship were TS38 kHz =−177.4+57log10 (L), (R2 = 0.86); TS120 kHz = −129.9+31.56log10 (L), (R2 =0.87); and TS200 kHz =−117.6+24.66log10 (L), (R2 =0.84). Empirical estimates of the relationship between the TS and body length of ice krill were established at 38, 120, and 200 kHz and compared with predictions obtained from both the linear regression model of Greene et al. (1991) and the Stochastic Distorted Wave Born Approximation (SDWBA) model. This result might be applied to improve acoustic detection and density estimation of ice krill in the Southern Ocean. Further comparative studies are needed with in situ target strength including various body lengths of ice krill.

High density of ice krill (Euphausia crystallorophias) in the Amundsen sea coastal polynya, Antarctica

High densities of ice krill Euphausia crystallorophias were observed along six acoustic transects within the Amundsen Sea Coastal Polynya, Antarctica. Two-frequency acoustic backscatter data was examined in the austral summers of January 2011 and February 2012. A dB identification window (Sv120−38) identified ice krill dominating the acoustic backscatter. The density of ice krill, calculated with the stochastic distorted-wave born approximation model, ranged between 4.5 and 30g wet mass m−2 for each transect (a mean of 16g wet mass m−2 for all transects), these high values are an order of magnitude higher than recorded previously in the Ross Sea Polynya. High densities were detected along the ice shelf and near the boundary between pack ice and coastal polynya, and we postulate that these could be important habitats for ice krill. The high densities observed along the transects make ice krill a potentially important, but poorly known contributor to these high-latitude shelf food webs.

Use of oxygen microsensors to measure the respiration rates of five dominant copepods and Euphausia crystallorophias furcilia from the Amundsen Sea, West Antarctica

The individual respiration rates of five biomass-dominant copepods (Calanoides acutus, Rhincalanus gigas, Metridia gerlachei, Calanus propinquus and Paraeuchaeta antarctica), and Euphausia crystallorophias furcilia, from the Amundsen Sea, West Antarctica, were determined using a Clark-type oxygen microsensor affording high temporal resolution. Measurements were conducted on specimens collected from waters exhibiting a very narrow temperature range (−1.68 to −1.32 °C), at sites located between 71 and 75°S, during the summer (31 January–20 March 2012). A short incubation time (3 h) was sufficient to reveal significant declines in dissolved oxygen concentrations by 12–45%. The respiration rates of the copepods and E. crystallorophias furcilia were within the ranges of previously reported values. The respiration rates of relatively large-bodied species were rather low, whereas the smaller species generally exhibited higher respiration rates. The data show that this simple microsensor technique is a useful high-resolution non-invasive means of investigating the metabolism of zooplankton in the Southern Ocean. The method could be used in other situations when such information is required.

Characterizing foodweb structure to identify potential ecosystem effects of fishing in the Ross Sea, Antarctica

AbstractThe potential ecosystem effects of fishing for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region were investigated. Mixed trophic impact analysis was applied to a model of the Ross Sea foodweb and used to calculate the relative trophic importances of species and trophic groups in the system. The trophic impact of toothfish on medium-sized demersal fish was identified as the strongest top-down interaction in the system based on multiple-step analysis. This suggests a potential for a strong predation-release effect on some piscine prey of toothfish (especially grenadiers and ice-fish on the Ross Sea slope). However, Antarctic toothfish had moderate trophic importance in the Ross Sea foodweb as a whole, and the analysis did not support the hypothesis that changes to toothfish will cascade through the ecosystem by simple trophic effects. Because of limitations of this kind of analysis, cascading effects on the Ross Sea ecosystem due to changes in the abundance of toothfish cannot be ruled out, but for such changes to occur a mechanism other than simple trophic interactions is likely to be involved. Trophic importances were highest in the middle of the foodweb where silverfish and krill are known to have a key role in ecosystem structure and function. The six groups with the highest indices of trophic importance were (in decreasing order): phytoplankton, mesozooplankton, Antarctic silverfish, small demersal fish, Antarctic krill and cephalopods. Crystal krill and small pelagic fish also had high trophic importance in some analyses. Strengths and limitations of this kind of analysis are presented. In particular, it is noted that the analysis only considers trophic interactions at the spatial, temporal and ecological scale of the whole Ross Sea shelf and slope area, averaged over a typical year and in 35 trophic groups. Interference and density-dependent effects were not included in this analysis. Effects at smaller spatial and temporal scales, and effects concerning only parts of populations, were not resolved by the analysis, and this is likely to underestimate the potential risks of fishing to Weddell seals and type-C killer whales.

Decrease in stomach contents in the Antarctic minke whale (Balaenoptera bonaerensis) in the Southern Ocean

The Antarctic minke whale (Balaenoptera bonaerensis) is one of the major krill predators in Antarctic waters. A reported decline in energy storage over almost two decades indicates that food availability for the whales may also have declined recently. To test this hypothesis, catch data from 20 survey years in the Japanese Whale Research Program in the Antarctic (JARPA) and its second phase (JARPA II) (1990/91–2009/10), which covered the longitudinal sector between 35°E and 145°W south of 58°S, were used to investigate whether there was any annual trend in the stomach contents weight of Antarctic minke whales. A linear mixed-effects analysis showed a 31 % (95 % CI 12.6–45.3 %) decrease in the weight of stomach contents over the 20 years since 1990/1991. A similar pattern of decrease was found in both males and females, except in the case of females sampled at higher latitude in the Ross Sea. These results suggest a decrease in the availability of krill for Antarctic minke whales in the lower latitudinal range of the research area. The results are consistent with the decline in energy storage reported previously. The decrease in krill availability could be due to environmental changes or to an increase in the abundance of other krill-feeding predators. The latter appears somewhat more likely, given the recent rapid recovery of humpback whale. Furthermore, humpback whales are not found in the Ross Sea, where both Antarctic krill and ice krill (Euphausia crystallorophias) are available, and where no change in prey availability for Antarctic minke whales is indicated.

Feeding of dominant zooplankton in Prydz Bay, Antarctica, during austral spring/summer: food availability and species responses

Information on the food and predation of zooplankton species is essential for an improved understanding of zooplankton community dynamics of the Southern Ocean. Feeding of dominant zooplankton species at locations across the neritic, slope and oceanic regions of Prydz Bay, Antarctica, was investigated with incubation experiments during austral spring/summer of 2009/2010 to identify the response of dominant copepods and krill to different feeding environments. Results showed distinct spatial and temporal variations in ingestion and filtration of predominant copepods and krill. In late spring, Calanoides acutus was inactive and the ingestion rate was only 1.30 μgC/ind/day. During early summer, a diatom bloom was in progress at station IS21, showing a peak biomass of Thalassiosira spp. and Fragilaria spp. Daily ingestion rates of Euphausia crystallorophias, C. acutus, Metridia gerlachei and Ctenocalanus citer were relatively high. By contrast, copepod ate predominantly ciliates in slope and oceanic regions where microplankton biomass were lower (<20 μgC/L). During late summer, microplankton of neritic regions, mainly composed of nano-sized Pseudo-nitzschia spp. and ciliates, was less than 10 μgC/L. C. acutus incubated in neritic regions mainly ate ciliates. The total microplankton biomass was lower (<5 μgC/L) and predominated by Pseudo-nitzschia spp. in slope regions north of Fram Bank, and daily ingestion rates of incubated copepods were less than 2.5 μgC/ind. Our results clearly demonstrated that copepods and krill had flexible feeding strategies to cope with temporally and spatially changing food availability in Prydz Bay. Meanwhile, ciliates appeared to represent an important carbon source for zooplankton, especially in regions with lower food concentrations.

Transcriptome and Peptidome Characterisation of the Main Neuropeptides and Peptidic Hormones of a Euphausiid: The Ice Krill, Euphausia crystallorophias

BackgroundThe Ice krill, Euphausia crystallorophias is one of the species at the base of the Southern Ocean food chain. Given their significant contribution to the biomass of the Southern Ocean, it is vitally important to gain a better understanding of their physiology and, in particular, anticipate their responses to climate change effects in the warming seas around Antarctica.Methodology/Principal FindingsIllumina sequencing was used to produce a transcriptome of the ice krill. Analysis of the assembled contigs via two different methods, produced 36 new pre-pro-peptides, coding for 61 neuropeptides or peptide hormones belonging to the following families: Allatostatins (A, B et C), Bursicon (α and β), Crustacean Hyperglycemic Hormones (CHH and MIH/VIHs), Crustacean Cardioactive Peptide (CCAP), Corazonin, Diuretic Hormones (DH), the Eclosion Hormone (EH), Neuroparsin, Neuropeptide F (NPF), small Neuropeptide F (sNPF), Pigment Dispersing Hormone (PDH), Red Pigment Concentrating Hormone (RPCH) and finally Tachykinin. LC/MS/MS proteomics was also carried out on eyestalk extracts, which are the major site of neuropeptide synthesis in decapod crustaceans. Results confirmed the presence of six neuropeptides and six precursor-related peptides previously identified in the transcriptome analyses.ConclusionsThis study represents the first comprehensive analysis of neuropeptide hormones in a Eucarida non-decapod Malacostraca, several of which are described for the first time in a non-decapod crustacean. Additionally, there is a potential expansion of PDH and Neuropeptide F family members, which may reflect certain life history traits such as circadian rhythms associated with diurnal migrations and also the confirmation via mass spectrometry of several novel pre-pro-peptides, of unknown function. Knowledge of these essential hormones provides a vital framework for understanding the physiological response of this key Southern Ocean species to climate change and provides a valuable resource for studies into the molecular phylogeny of these organisms and the evolution of neuropeptide hormones.