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Padmini Dalpadado - One of the best experts on this subject based on the ideXlab platform.
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Distribution and abundance of euphausiids and pelagic amphipods in Kongsfjorden, Isfjorden and Rijpfjorden (Svalbard) and changes in their relative importance as key prey in a warming marine ecosystem
Polar Biology, 2016Co-Authors: Padmini Dalpadado, Jon Rønning, Vladimir Pavlov, Erik Sperfeld, Friedrich Buchholz, Anette WoldAbstract:Euphausiid (krill) and amphipod dynamics were studied during 2006–2011 by use of plankton nets in Kongsfjorden (79°N) and adjacent waters, also including limited sampling in Isfjorden (78°N) and Rijpfjorden (80°N). The objectives of the study were to assess how variations in physical characteristics across fjord systems affect the distribution and abundance of euphausiids and amphipods and the potential for these macrozooplankton species to reproduce in these waters. The abundances of euphausiids and amphipods were higher in Kongsfjorden than in Rijpfjorden and Isfjorden, and the highest abundances were observed at the innermost stations of Kongsfjorden, where Thysanoessa inermis and Themisto Libellula dominated. The Atlantic species Thysanoessa longicaudata , Meganyctiphanes norvegica and Themisto abyssorum dominated at the outside Kongsfjorden. Inter-annual and seasonal variability in abundances of euphausiids and amphipods were evident. The presence of ripe euphausiids outside Kongsfjorden indicates that they may reproduce in these areas. Mature individuals of T. abyssorum were recorded mainly outside Kongsfjorden, whereas no mature or ripe T. Libellula were present in both the inner and outer parts of this fjord. If the warming trend persists, as seen during the last decade, this would favour the Atlantic/boreal euphausiid species, while Arctic species, such as the amphipod T. Libellula , may decline. Euphausiids and amphipods are major food of capelin ( Mallotus villosus ) and polar cod ( Boreogadus saida ), respectively, in this region, and changes in prey abundance will likely have an impact on the feeding dynamics of these important fish species.
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Inter-specific variations in distribution, abundance and reproduction strategies of krill and amphipods in the Marginal Ice Zone of the Barents Sea
Deep-sea Research Part Ii-topical Studies in Oceanography, 2008Co-Authors: Padmini Dalpadado, Bjørnar Ellertsen, Signe JohannessenAbstract:Abstract The krill Thysanoessa inermis and Thysanoessa longicaudata and the hyperiid amphipods Themisto abyssorum and Themisto Libellula are important components of the pelagic ecosystem in the Marginal Ice Zone (MIZ) of the northwestern Barents Sea. High abundance of krill (336 no. m−2) and amphipods (107 no. m−2) was recorded at a station close to 81.4°N, north of Spitsbergen. Statistical splitting of length frequency distributions gave 3–4 cohorts for T. inermis and up to three cohorts for T. longicaudata. In the current study, up to three and five cohorts were recorded for T. abyssorum and T. Libellula, respectively, with the majority belonging to 0-group. The distribution of Atlantic/boreal species of krill and amphipods seemed to be mainly restricted to the deeper Atlantic waters (>200 m). The cold waters in the MIZ seem to act as a barrier towards the reproduction of several dominant Thysanoessa species. Thus, the advection processes from the south appear to be important for maintaining the krill population in the high-arctic waters. In contrast to krill, specifically, the cold-water amphipod, T. Libellula, seems to breed successfully in the MIZ.
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Inter-specific variations in distribution, abundance and possible life-cycle patterns of Themisto spp. (Amphipoda) in the Barents Sea
Polar Biology, 2002Co-Authors: Padmini DalpadadoAbstract:Amphipods from the central and northern areas of the Barents Sea were studied by a series of MOCNESS profiles between 1990 and 1997. Themisto abyssorum, though dominant in warmer Atlantic water, was also present in Arctic water. In contrast, T. Libellula was a typical Arctic species and penetrated very little into the Atlantic water masses. T. compressa was seldom found in the studied area. Linear regression analysis showed a statistically significant negative relationship between abundance of T. Libellula and the variability in the Atlantic inflow. The abundance of this species seems to be, to a large extent, determined by the amount of Arctic water in the Barents Sea. The sub-Arctic species, T. abyssorum, only has a 1-year life-cycle, with the peak in release of young (2–3 mm) occurring in May and June. A few individuals may survive to be older. The Arctic species, T. Libellula, seems to release the young earlier and the length-frequency distributions seem to indicate a 2-year life-span. The spring phytoplankton, which usually blooms during April in the Barents Sea, followed by high abundance of Calanus spp. and krill species, are regarded as important factors that influence the release of the amphipods' young.
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Distribution of Themisto (Amphipoda) spp. in the Barents Sea and predator-prey interactions
ICES Journal of Marine Science, 2001Co-Authors: Padmini Dalpadado, Nina Borkner, Bjarte Bogstad, Sigbjørn MehlAbstract:Dalpadado, P., Borkner, N., Bogstad, B., and Mehl, S. 2001. Distribution of Themisto (Amphipoda) spp. in the Barents Sea and predator-prey interactions. – ICES Journal of Marine Science, 58: 876–895. Themisto abyssorum and Themisto Libellula were the dominant amphipod species observed in the central and the northern Barents Sea during 1984–1996. T. abyssorum was predominant in the subarctic waters, T. Libellula in the Arctic waters. A third species, Themisto compressa, was rare and was restricted to the Atlantic waters. Our study showed peak abundances of T. abyssorum and T. Libellula in summer and in early autumn. High abundances were usually associated with Polar Front waters. T. Libellula has a more near surface distribution than T. abyssorum. Followed by a decrease in the capelin stock from 1985–1987 there was an increase in the abundance of Themisto abyssorum and T. Libellula, probably due to the reduced grazing pressure from capelin (Mallotus villosus). In the mid-1980s and 1990s when the capelin stock was at extremely low levels, cod (Gadus morhua) switched from capelin to alternative prey such as amphipods and krill. Detailed analysis of amphipods in the cod stomachs from 1984–1999, showed that cod fed mainly on Themisto spp., especially on T. Libellula. Themisto species were consumed by most age groups of cod. With an increase in the capelin stock from 1987–1991, a corresponding decrease in the abundance of Themisto abyssorum and T. Libellula was observed. During 1993– 1996 when the capelin stock again was at low levels, the abundance of these two amphipod species increased. The increase in abundance was less pronounced in the mid-1990s for T. Libellula probably owing to higher grazing pressure from cod and other predators such as harp seal (Phoca groenlandica) and arctic sea birds. The stock size of cod in the mid-1990s was about twice the amount as in the mid-1980s. These results illustrate strong predator-prey interactions between macrozooplankton species as amphipods and capelin and cod in the Barents Sea. The amphipod populations in the Barents Sea appear to be to a large extent controlled by predation.
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Distribution and life history of krill from the Barents Sea
Polar Research, 1991Co-Authors: Padmini Dalpadado, Hein Rune SkjoldalAbstract:Two dominant hyperiid amphipod species were found in the western and central Barents Sea, Themisto abyssonun and T. Libellula. T. abyssona was predominant in the boreal and subarctic waters, T. Libellula in the Arctic waters. T. compressa was rare and was restricted to the Atlantic waters. The subarctic species T. abyssonun has a one year life cycle, with the release of young (2-3 mm) in the May-June period. The Arctic species T. Libellula seems to release their young earlier and have a prolonged breeding period. Both species release their young during the period of spring phytoplankton bloom in the Barents Sea. Our study shows peak aboundances of T. abyssonun and T. Libellula in summer and in early autumn. High abundances, up to 122 individuals per m2 of T. abyssorum were observed south and south east of Svalbard Bank in July and October 1988. Very high abundances, up to 430 individuals per m2 of T. Libellula were recorded in May-June 1987 and July 1988 close to the Polar Front region (at approx. 76°N, 30- 32°E). Followed by a decrease in the capelin stock from 1986 to 1987, there was an increase in the abundance of T. abyssorum and T. Libellula, probably owing to the reduced grazing pressure from capelin. With an increase in the capelin stock from 1987 up to 1991, a decrease in abundance of T. abyssonun and T. Libellula was obsemed, indicating predator-prey interactions between capelin and their prey-amphipods.NORSK SAMMENDRAG:To arter av hyperide amfipoder er dominerende i Barentshavet; Themisto abyssorum og T. Libellula. T. abyssonun dominerte i subarktisk vann og T. Libellula i arktisk vann. T. compressa var sjelden og ble kun funnet i atlantiske vannmasser. Den subarktiske arten T. abyssorum har en ettårig livssyklus og yngelen (2-3 mm) frigjøres i mai-juni. Den arktiske arten T. Libellula synes å frigjøre yngelen noe tidligere, og har en lengre gyteperiode. Begge artene friggjøyr ngelen under våroppblomstringen i Barentshavet. Våre undersøkelser viser størst tetthet av T. abyssonun og T. Libellula om sommeren og tidlig på høsten.Høye tettheter, opp til 122 individer m2 av T. abyssorum ble observert sør og sørøst av Svalbardbanken i juli og oktober 1988. Svært høye ko nsentrasjoner, opp til 430 individer m-2 ,av T. Libellula ble observert i mai-juni 1987 og i juli 1988 nær polarfronten (omkring 76°N, 30-32°E). Etter en reduksjon i loddebestanden fra 1986 til 1987 økte mengden av T. abyssonun og T. Libellula, trolig på grum av lavere beitetrykk fra lodde. Da loddebestanden økte fra 1987 til 1991, avtok mengden av T. abyssorum og T. Libellula. Dette tyder på at det er et predator-bytteforhold mellom lodde og amfipoder
Patrick Mayzaud - One of the best experts on this subject based on the ideXlab platform.
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ORIGINAL PAPER Growth and lipid class composition of the Arctic pelagic amphipod Themisto Libellula
2016Co-Authors: Margaux Noyon, Fanny Narcy, Patrick MayzaudAbstract:Abstract Carnivorous zooplankton is a key element to the energy transfer through the arctic food web, linking lipid rich herbivores to the top predators. We investigated the growth and lipid dynamic of the Arctic pelagic amphipod Themisto Libellula in Kongsfjorden (Svalbard, 79N) from May to October 2007. Additional samplings were performed in spring and summer 2006 and further north in Rijpfjorden (80N), in September 2006 and 2007. In Kongsfjorden, the first free-swimming stages (3 mm) appeared early May and reached their adult length (25 mm), in October. During their first year, they grew according to a Von Bertalanffy model and most probably constituted a single cohort. Juveniles had the highest growth rate (0.19 mm day-1) and revealed relatively low total lipid (TL) content (about 2.5 % wet weight (WW)) with phospholipids as the major lipid class. Sub-adults showed a distinct decrease of growth rates which coin-cided with the increase of neutral lipid storage, reflecting a switch in energy allocation, from somatic growth to lipid storage. Indeed wax esters (WE) increased up to 48.5 % TL on average in adults in 2006 while triacylgly-cerols (TAG) remained almost constant below 25.2 % TL. The absence of lipid accumulation (in disproportion of the weight) in 2007 could be explained by a higher metabo-lism of T. Libellula or preys of lower quality. In Rijpf-jorden, adults in their second year continued accumulating lipid (up to 10 % WW) with high and similar proportions of both lipid classes, WE and TAG. We highlighted that T. Libellula exhibited a variable lipid metabolism along its life cycle depending on its physiological needs and environmental conditions
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Ontogenic variations in fatty acid and alcohol composition of the pelagic amphipod Themisto Libellula in Kongsfjorden (Svalbard)
Marine Biology, 2011Co-Authors: Margaux Noyon, Stéphane Gasparini, Fanny Narcy, Patrick MayzaudAbstract:The fatty acid and alcohol composition of the pelagic amphipod, Themisto Libellula, was monitored during the 5 first months of its life cycle (4–20 mm length) in an Arctic fjord, Kongsfjorden, Svalbard. Fatty acids of the three major lipid classes, polar lipids (PL), triacylglycerol (TAG), and wax esters (WE), were analyzed to highlight ontogenic changes in their diet and metabolism. The PL composition of T. Libellula did not show any strong variations along their growth except during the first month where an important increase of 20:5(n-3) (EPA) and 22:6(n-3) (DHA) was observed. The TAG composition revealed a clear gradient corresponding to a diet shift from omnivorous juveniles toward carnivorous sub-adults and adults. Indeed, fatty acid trophic markers of diatoms were dominant in the juveniles, whereas 20:1(n-9) and 22:1(n-11), the Calanus sp. trophic markers, overwhelmed in the older stages. The WE composition highlighted the same general trend, however, differences were found with the TAG and are discussed as a result of differences in turnover rates and assimilation pathways between the two lipid classes.
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Growth and lipid class composition of the Arctic pelagic amphipod Themisto Libellula.
Marine biology, 2011Co-Authors: Margaux Noyon, Stéphane Gasparini, Fanny Narcy, Patrick MayzaudAbstract:Carnivorous zooplankton is a key element to the energy transfer through the arctic food web, linking lipid rich herbivores to the top predators. We investigated the growth and lipid dynamic of the Arctic pelagic amphipod Themisto Libellula in Kongsfjorden (Svalbard, 79°N) from May to October 2007. Additional samplings were performed in spring and summer 2006 and further north in Rijpfjorden (80°N), in September 2006 and 2007. In Kongsfjorden, the first free-swimming stages (3 mm) appeared early May and reached their adult length (25 mm), in October. During their first year, they grew according to a Von Bertalanffy model and most probably constituted a single cohort. Juveniles had the highest growth rate (0.19 mm day−1) and revealed relatively low total lipid (TL) content (about 2.5% wet weight (WW)) with phospholipids as the major lipid class. Sub-adults showed a distinct decrease of growth rates which coincided with the increase of neutral lipid storage, reflecting a switch in energy allocation, from somatic growth to lipid storage. Indeed wax esters (WE) increased up to 48.5% TL on average in adults in 2006 while triacylglycerols (TAG) remained almost constant below 25.2% TL. The absence of lipid accumulation (in disproportion of the weight) in 2007 could be explained by a higher metabolism of T. Libellula or preys of lower quality. In Rijpfjorden, adults in their second year continued accumulating lipid (up to 10% WW) with high and similar proportions of both lipid classes, WE and TAG. We highlighted that T. Libellula exhibited a variable lipid metabolism along its life cycle depending on its physiological needs and environmental conditions.
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Feeding of Themisto Libellula (Amphipoda Crustacea) on natural copepods assemblages in an Arctic fjord (Kongsfjorden, Svalbard)
Polar Biology, 2009Co-Authors: Margaux Noyon, Stéphane Gasparini, Patrick MayzaudAbstract:Ingestion rates and selectivity of the Arctic pelagic amphipod Themisto Libellula were studied experimentally in Kongsfjorden (Svalbard, 78°N) during the summer period. Feeding incubations were conducted on naturally occurring copepod communities at different concentrations ranging from 25 to 250 preys L^−1. The ingestion rates increased with food availability from 1.3 to 17.7 preys ind^−1 day^−1, which corresponded to 0.3–11% of body carbon day^−1. Despite the high prey concentration used in the experiments the satiation level was not reached. We suggested that T. Libellula is able to take the maximum benefit from dense patches of preys, which represent a good adaptation to the high variability in food supply characteristic of polar environment. Copepodids stage III of Calanus spp. appeared to be the preferred preys of T. Libellula . Smaller copepods such as Oithona similis and Pseudocalanus spp., were also selected but only when their relative abundance exceeded 25% of the total prey available. The potential predation impact of T. Libellula is discussed in relation to the mesozooplankton small-scale patchiness and predator abundance.
Margaux Noyon - One of the best experts on this subject based on the ideXlab platform.
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ORIGINAL PAPER Growth and lipid class composition of the Arctic pelagic amphipod Themisto Libellula
2016Co-Authors: Margaux Noyon, Fanny Narcy, Patrick MayzaudAbstract:Abstract Carnivorous zooplankton is a key element to the energy transfer through the arctic food web, linking lipid rich herbivores to the top predators. We investigated the growth and lipid dynamic of the Arctic pelagic amphipod Themisto Libellula in Kongsfjorden (Svalbard, 79N) from May to October 2007. Additional samplings were performed in spring and summer 2006 and further north in Rijpfjorden (80N), in September 2006 and 2007. In Kongsfjorden, the first free-swimming stages (3 mm) appeared early May and reached their adult length (25 mm), in October. During their first year, they grew according to a Von Bertalanffy model and most probably constituted a single cohort. Juveniles had the highest growth rate (0.19 mm day-1) and revealed relatively low total lipid (TL) content (about 2.5 % wet weight (WW)) with phospholipids as the major lipid class. Sub-adults showed a distinct decrease of growth rates which coin-cided with the increase of neutral lipid storage, reflecting a switch in energy allocation, from somatic growth to lipid storage. Indeed wax esters (WE) increased up to 48.5 % TL on average in adults in 2006 while triacylgly-cerols (TAG) remained almost constant below 25.2 % TL. The absence of lipid accumulation (in disproportion of the weight) in 2007 could be explained by a higher metabo-lism of T. Libellula or preys of lower quality. In Rijpf-jorden, adults in their second year continued accumulating lipid (up to 10 % WW) with high and similar proportions of both lipid classes, WE and TAG. We highlighted that T. Libellula exhibited a variable lipid metabolism along its life cycle depending on its physiological needs and environmental conditions
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Ontogenic variations in fatty acid and alcohol composition of the pelagic amphipod Themisto Libellula in Kongsfjorden (Svalbard)
Marine Biology, 2011Co-Authors: Margaux Noyon, Stéphane Gasparini, Fanny Narcy, Patrick MayzaudAbstract:The fatty acid and alcohol composition of the pelagic amphipod, Themisto Libellula, was monitored during the 5 first months of its life cycle (4–20 mm length) in an Arctic fjord, Kongsfjorden, Svalbard. Fatty acids of the three major lipid classes, polar lipids (PL), triacylglycerol (TAG), and wax esters (WE), were analyzed to highlight ontogenic changes in their diet and metabolism. The PL composition of T. Libellula did not show any strong variations along their growth except during the first month where an important increase of 20:5(n-3) (EPA) and 22:6(n-3) (DHA) was observed. The TAG composition revealed a clear gradient corresponding to a diet shift from omnivorous juveniles toward carnivorous sub-adults and adults. Indeed, fatty acid trophic markers of diatoms were dominant in the juveniles, whereas 20:1(n-9) and 22:1(n-11), the Calanus sp. trophic markers, overwhelmed in the older stages. The WE composition highlighted the same general trend, however, differences were found with the TAG and are discussed as a result of differences in turnover rates and assimilation pathways between the two lipid classes.
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Growth and lipid class composition of the Arctic pelagic amphipod Themisto Libellula.
Marine biology, 2011Co-Authors: Margaux Noyon, Stéphane Gasparini, Fanny Narcy, Patrick MayzaudAbstract:Carnivorous zooplankton is a key element to the energy transfer through the arctic food web, linking lipid rich herbivores to the top predators. We investigated the growth and lipid dynamic of the Arctic pelagic amphipod Themisto Libellula in Kongsfjorden (Svalbard, 79°N) from May to October 2007. Additional samplings were performed in spring and summer 2006 and further north in Rijpfjorden (80°N), in September 2006 and 2007. In Kongsfjorden, the first free-swimming stages (3 mm) appeared early May and reached their adult length (25 mm), in October. During their first year, they grew according to a Von Bertalanffy model and most probably constituted a single cohort. Juveniles had the highest growth rate (0.19 mm day−1) and revealed relatively low total lipid (TL) content (about 2.5% wet weight (WW)) with phospholipids as the major lipid class. Sub-adults showed a distinct decrease of growth rates which coincided with the increase of neutral lipid storage, reflecting a switch in energy allocation, from somatic growth to lipid storage. Indeed wax esters (WE) increased up to 48.5% TL on average in adults in 2006 while triacylglycerols (TAG) remained almost constant below 25.2% TL. The absence of lipid accumulation (in disproportion of the weight) in 2007 could be explained by a higher metabolism of T. Libellula or preys of lower quality. In Rijpfjorden, adults in their second year continued accumulating lipid (up to 10% WW) with high and similar proportions of both lipid classes, WE and TAG. We highlighted that T. Libellula exhibited a variable lipid metabolism along its life cycle depending on its physiological needs and environmental conditions.
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Feeding of Themisto Libellula (Amphipoda Crustacea) on natural copepods assemblages in an Arctic fjord (Kongsfjorden, Svalbard)
Polar Biology, 2009Co-Authors: Margaux Noyon, Stéphane Gasparini, Patrick MayzaudAbstract:Ingestion rates and selectivity of the Arctic pelagic amphipod Themisto Libellula were studied experimentally in Kongsfjorden (Svalbard, 78°N) during the summer period. Feeding incubations were conducted on naturally occurring copepod communities at different concentrations ranging from 25 to 250 preys L^−1. The ingestion rates increased with food availability from 1.3 to 17.7 preys ind^−1 day^−1, which corresponded to 0.3–11% of body carbon day^−1. Despite the high prey concentration used in the experiments the satiation level was not reached. We suggested that T. Libellula is able to take the maximum benefit from dense patches of preys, which represent a good adaptation to the high variability in food supply characteristic of polar environment. Copepodids stage III of Calanus spp. appeared to be the preferred preys of T. Libellula . Smaller copepods such as Oithona similis and Pseudocalanus spp., were also selected but only when their relative abundance exceeded 25% of the total prey available. The potential predation impact of T. Libellula is discussed in relation to the mesozooplankton small-scale patchiness and predator abundance.
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nutrition et dynamique lipidique de l hyperien themisto Libellula importance en terme de strategie
2009Co-Authors: Margaux NoyonAbstract:Themisto Libellula est un amphipode relativement peu etudie bien qu’omnipresent et abondant dans le plancton arctique. De part son regime alimentaire carnivore et en tant que proie pour de nombreux predateurs superieurs, il pourrait constituer un maillon important de la chaine alimentaire et contribuer de facon significative aux transferts energetiques. Les principaux objectifs de cette these sont: i) de comprendre comment T. Libellula est adapte aux conditions polaires, ii) de connaitre son role trophodynamique. En 2006 et 2007, de mai a octobre, des prelevements et des experiences ont ete realises dans le Kongsfjorden, fjord situe sur la cote Ouest des Svalbard (79° N). Les resultats montrent que l’energie alimentaire est investie dans la croissance au cours des premiers mois de vie (printemps) puis stockee sous forme de lipides a forte valeur energetique (ete-automne). L’analyse des acides gras comme marqueurs trophiques a mis en evidence un changement de regime alimentaire au cours du developpement, les individus les plus jeunes adoptant un regime mixte phytoplancton - zooplancton et les plus âges un regime compose principalement de copepodes du genre Calanus. Des experiences complementaires de predation ont permis de preciser les taux d’ingestion journalier et la selectivite de T. Libellula. Dans leur ensemble, les resultats montrent une bonne synchronisation entre le cycle de vie de T. Libellula et la dynamique des niveaux trophiques inferieurs. La surabondance de ressources alimentaires par rapport a leurs besoins et la faible pression de predateurs potentiels dans la zone suggerent que le Kongsfjorden constitue une aire de nourricerie ideale pour les juveniles et les sub-adultes de T. Libellula.
Alexei I. Pinchuk - One of the best experts on this subject based on the ideXlab platform.
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Spatial genetic structure in Themisto Libellula (Amphipoda: Hyperiidae) from the coastal Gulf of Alaska, Bering and Chukchi seas
Polar Biology, 2020Co-Authors: Astrid Tempestini, Alexei I. Pinchuk, France DufresneAbstract:Arctic marine ecosystems are undergoing rapid biogeographic responses to climate changes following the highest warming rates observed around the globe in recent decades. These drastic changes undoubtfully affect gene flow and genetic structure in the polar and subpolar regions. Here, we examine the genetic structure of the cold-water holozooplankton hyperiid Themisto Libellula (Amphipoda: Hyperiidae), a key species in the Arctic ecosystem, using molecular population genetic approach. For the first time, we examine and compare populations across the Arcto-Pacific sector of the species biographical range from the northern Gulf of Alaska through the northern Chukchi Sea. We hypothesized that the complex history of the North Pacific and Amerasian Arctic marked by periodic intermissions and restrictions of the dominant northward flow resulted in vicariant differentiation of T. Libellula along the latitudinal gradient. Mitochondrial and Rad-sequencing analyses revealed little genetic differentiation between closely connected Arctic populations in the Arctic Chukchi and Bering seas. In contrast, population from sub-Arctic glacial fjords in the Gulf of Alaska were distinct with few shared COI haplotypes. Strong F _ST estimates ( F _ST = 0.16) based on 5197 neutral SNPs between the Gulf of Alaska and Bering Sea populations indicated very limited exchanges despite an existing connection between the areas via the Alaska Coastal Current. Our results suggest strong opportunities for genetic differentiation among marine zooplankton populations along the Pacific Alaskan coast and from the Arctic marginal seas.
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Emergence of the Arctic Themisto Libellula (Amphipoda: Hyperiidae) on the southeastern Bering Sea shelf as a result of the recent cooling, and its potential impact on the pelagic food web
ICES Journal of Marine Science, 2013Co-Authors: Alexei I. Pinchuk, Kenneth O. Coyle, Edward V. Farley, Heather M. RennerAbstract:The eastern Bering Sea shelf experienced a sequence of warm years after a regime shift in the late 1970s. Following a series of unusually warm years in the early 2000s, the climate shifted again in 2007 to a series of extremely cold years that were marked by intense ice coverage and late ice retreat. Spatial and temporal variability in zooplankton communities during the recent cold period was investigated as part of the collaborative BEST-BSIERP program. An increasing presence of the Arctic hyperiid Themisto Libellula, which had not been reported from the southeastern Bering Sea since the 1970s, was observed in the Middle Shelf Domain, indicating a developing structural shift in the zooplankton community in response to continuous cold conditions. Simultaneously, T. Libellula became an increasingly dominant prey in the diets of zooplanktivorous fish and seabirds, demonstrating the important role for T. Libellula in the pelagic food web. Our analysis suggests that T. Libellula is capable of controlling copepod populations, thus it may become a potential contributor to top-down regulation of Calanus spp. in the eastern Bering Sea.
Stig Falk-petersen - One of the best experts on this subject based on the ideXlab platform.
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Feeding in Arctic darkness: mid-winter diet of the pelagic amphipods Themisto abyssorum and T. Libellula
Marine Biology, 2012Co-Authors: Angelina Kraft, Jørgen Berge, Øystein Varpe, Stig Falk-petersenAbstract:The pelagic amphipods Themisto abyssorum and Themisto Libellula represent important links between the herbivore zooplankton community and higher trophic levels of the Arctic marine food webs. Large double structured eyes of both of these hyperiid species are assumed to be used for visual prey detection. However, no information is available on the feeding strategies of these visually searching predators for the period of the polar night, a time of year with no or very low levels of daylight. Here, we report on the stomach and gut content of both Themisto species collected during a January expedition around Svalbard (78° to 81°N). Results indicate that T. abyssorum and T. Libellula feed actively during the Arctic winter. The major food source of both amphipods consisted of calanoid copepods, most frequently Calanus finmarchicus.
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Population dynamics and body composition of the Arctic hyperiid amphipod Themisto Libellula in Svalbard fjords
Polar Biology, 2006Co-Authors: Kjersti Dale, Haakon Hop, Stig Falk-petersen, Svein-erik FevoldenAbstract:Population structure, growth and body composition (wet-, dry-, ash weight and total lipid) of the Arctic pelagic amphipod Themisto Libellula were studied in four fjords on West Spitsbergen, Svalbard, from July to December 2000 and in April 2002. In one of the fjords, Kongsfjorden, growth of T. Libellula was calculated as the change in mean length of the 0+ cohort from July to December. The young were released from the brood pouches in early spring (March–April). Summer growth was 3.5 mm month−1, whereas growth during the autumn was only 0.6 mm month−1. The size frequency distributions indicated a 2–2.5 year life-span. The size structure of the population in Hornsund, the southernmost fjord on Spitsbergen, indicated a delayed time of spawning. The storage of lipids in T. Libellula occurred during late summer and towards the winter, when the food items contain the maximum amount of stored lipids.
