Structure et résilience des réseaux trophiques benthiques de l'Arctique canadien et de la mer des Tchouktches

RÉSUMÉ: Les changements climatiques actuels sont à l’origine de nombreuses modifications dans l’océan Arctique, telles qu’une augmentation de la température des eaux de surface, une augmentation des apports fluviaux, une réduction dans la couverture de glace de mer, des changements de composition des espèces ou des changements dans la phénologie et l’intensité de la production primaire. Ces changements pourraient être à l’origine de modifications dans la structure et le fonctionnement des réseaux trophiques benthiques. Il est nécessaire aujourd’hui de décrire la structure et la résilience de réseaux trophiques benthiques de ces régions pour évaluer l’impact des changements climatiques sur celles-ci. Cette étude a pour objectifs de décrire la structure et la résilience des réseaux trophiques benthiques de l’Arctique canadien (polynie des eaux du Nord, archipel canadien, golfe d’Amundsen, mer de Beaufort) et de la mer des Tchouktches par une approche isotopique, et d’évaluer l’importance des algues de glace pour ces réseaux trophiques, à l’aide du biomarqueur d’algues de glace IP25 (Ice Proxy 25). Pour atteindre ces deux objectifs, nous avons collecté des échantillons de matière particulaire en suspension, de sédiments de surface, et de faune benthique de juillet à octobre 2014, à bord du NGCC Amundsen. Les valeurs en δ13C mesurées dans les sédiments de la polynie des eaux du Nord, de l’archipel canadien et de la mer des Tchoukches, traduisent une origine marine de la matière organique. La mer de Beaufort et le golfe d’Amundsen sont quant à eux caractérisés par des apports terrigènes et des apports mixtes (terrigènes et marins) respectivement. Ces différences dans l’origine de matière organique se retrouvent dans les signatures isotopiques des organismes et dans la structure des réseaux trophiques : la mer de Beaufort se distingue des autres régions par des signatures appauvries en 13C chez les consommateurs et par de nombreux organismes avec de hauts niveaux trophiques. La faible séparation trophique et la forte redondance trophique suggèrent que la polynie des eaux du Nord et l’archipel canadien semblent être les régions avec la plus grande possibilité de résilience face à des changements environnementaux. Nous avons mis en évidence la présence du marqueur d’algue de glace IP25 chez les organismes appartenant à tous les niveaux trophiques. Les plus fortes concentrations en IP25 ont été retrouvées chez les déposivores de surface. Les algues de glace semblent être une source de xv nourriture importante pour les organismes de l’archipel canadien, où les plus fortes concentrations en biomarqueurs d’algues de glace ont été retrouvées (en particulier chez les déposivores et les prédateurs) et pour la polynie des eaux du Nord où les signatures en carbone des organismes indiquent une assimilation d’algues de glace. -- Mot(s) clé(s) en français : Benthos, structure trophique, résilience, algues de glace, biomarqueur IP25, isotopes stables, Arctique Canadien, Mer des Tchouktches. -- ABSTRACT: Ongoing climate change is causing rapid changes in the Arctic Ocean, such as higher water temperatures, increased fluvial run-off, reduced sea-ice cover, change in species composition, change in the timing and intensity of primary production. Those changes will give rise to severe ecosystem changes propagating in benthic food web through all trophic levels. There is a need to establish benthic food web structure and resilience baseline for future comparison and to understand the impact of climate change in those various benthic food-webs. We also need a thorough study of the role of ice algae for the benthic food webs on a large scale. The objectives of this study were to describe the structure and the resilience of the benthic food-web of the Canadian Arctic and the Chukchi Sea (North Water Polynya, Canadian Archipelago, Amundsen Gulf, Beaufort Sea, Chukchi Sea), using stable carbon and nitrogen isotope analyses and to evaluate the importance of sea-ice algae in the benthic food-web using the Sea ice biomarkerIP25 (“Ice Proxy 25”). To reach these objectives, we collected suspended particulate organic matter, surface sediments and zoobenthic samples from July to October 2014 aboard the CCGS Amundsen. Values in δ13C in the sediment were indicative of a marine origin of the organic matter in the North Water Polynya, Canadian Archipelago and the Chukchi Sea. The Beaufort Sea was characterized by terrestrial input, and the Amundsen Gulf was characterized by a mix between terrestrial and marine input. Those differences in the origin of organic matter were mirrored in consumer isotopic signatures in all the regions. The Beaufort Sea differed from the other regions regarding the trophic structure. The high trophic redundancy and the low trophic separation of the North Water Polynya and the Canadian Archipelago suggest those regions have the higher potential of resilience facing environmental changes. We highlight transfer of ice algae across the different trophic levels. The biomarker IP25 was detectable in all the trophic guilds, and the higher concentrations were found in the surface deposit feeder. Ice algae seem to be an important food source for the Canadian Archipelago food web, were the higher concentration in IP25 were found and for the North Water Polynya, where the carbon stable isotopic signatures indicate ice algae assimilation. -- Mot(s) clé(s) en anglais : Benthos, trophic structure, resilience, ice-algae, IP25 biomarker, stable isotopes, Canadian arctic, Chukchi Sea

Southern Ocean food-webs and climate change: A short review and future directions

Food-webs are a critical feature of ecosystems and help us understand how communities will respond to climate change. The Southern Ocean is facing rapid and accelerating changes due to climate change. Though having evolved in an isolated and somewhat extreme environment, Southern Ocean biodiversity and food-webs are among the most vulnerable. Here, we review 1) current knowledge on Southern Ocean food-webs; 2) methods to study food-webs; 3) assessment of current and future impacts of climate change on Southern Ocean food-webs; 4) knowledge gaps; and 5) the role of Early Career Researchers (ECRs) in future studies. Most knowledge on Southern Ocean food-webs come from the pelagic environment, both at macro- and microbial levels. Modelling and diet studies of individual species are major contributors to the food-web knowledge. These studies revealed a short food-web, predominantly sustained by Antarctic Krill (Euphausia superba). Additionally, alternative pathways exist, involving other krill species, fish, and squid, which play equally important roles in connecting primary producers with top predators. Advantages and disadvantages of several techniques used to study Southern Ocean food-webs were identified, from the classical analyses of stomach contents, scats, or boluses to the most recent approaches such as metabarcoding and trophic-biomarkers. Observations show that climate change can impact the food-web in different ways. As an example, changes to smaller phytoplankton species can lengthen the food-web, increasing assimilation losses and/or changing nutrient cycles. Future studies need to focus on the benthic-dominated food-webs and the benthopelagic coupling. Furthermore, research during the winter season and below the ice-shelves is needed as these areas may play a crucial role in the functioning of this ecosystem. ECRs can play a significant role in advancing the study of Southern Ocean food-webs due to their willingness for interdisciplinary collaboration and proficiency in employing various methodologies, contributing to the construction of high-resolution food-webs.</jats:p

Southern Ocean food-webs and climate change:A short review and future directions

Food-webs are a critical feature of ecosystems and help us understand how communities will respond to climate change. The Southern Ocean is facing rapid and accelerating changes due to climate change. Though having evolved in an isolated and somewhat extreme environment, Southern Ocean biodiversity and food-webs are among the most vulnerable. Here, we review 1) current knowledge on Southern Ocean food-webs; 2) methods to study food-webs; 3) assessment of current and future impacts of climate change on Southern Ocean food-webs; 4) knowledge gaps; and 5) the role of Early Career Researchers (ECRs) in future studies. Most knowledge on Southern Ocean food-webs come from the pelagic environment, both at macro- and microbial levels. Modelling and diet studies of individual species are major contributors to the food-web knowledge. These studies revealed a short food-web, predominantly sustained by Antarctic Krill (Euphausia superba). Additionally, alternative pathways exist, involving other krill species, fish, and squid, which play equally important roles in connecting primary producers with top predators. Advantages and disadvantages of several techniques used to study Southern Ocean food-webs were identified, from the classical analyses of stomach contents, scats, or boluses to the most recent approaches such as metabarcoding and trophic-biomarkers. Observations show that climate change can impact the food-web in different ways. As an example, changes to smaller phytoplankton species can lengthen the food-web, increasing assimilation losses and/or changing nutrient cycles. Future studies need to focus on the benthic-dominated food-webs and the benthopelagic coupling. Furthermore, research during the winter season and below the ice-shelves is needed as these areas may play a crucial role in the functioning of this ecosystem. ECRs can play a significant role in advancing the study of Southern Ocean food-webs due to their willingness for interdisciplinary collaboration and proficiency in employing various methodologies, contributing to the construction of high-resolution food-webs

Seasonal and ocean basin-scale assessment of amino acid δ15N trends in a Southern Ocean marine predator

The Southern Ocean exhibits substantial spatio-temporal variation in biogeochemical processes that shape interactions and productivity across food webs. Stable isotopes in marine predators provide an opportunity to capture such variations, yet few studies have accounted for variability in the isotopic baseline when interpreting predator isotope values. Using bulk δ15N and δ13C values and the δ15N values of amino acids (AAs) of blood from female Antarctic fur seals (AFSs) Arctocephalus gazella, we investigated spatial and seasonal variation in baseline δ15N (δ15Nbaseline) values across 3 Southern Ocean basins (Indian, Pacific and Atlantic) to facilitate robust comparison of consumer trophic ecology. We detected spatial and seasonal differences in δ15Nbaseline values across the basins, using the source AAs phenylalanine (Phe) and lysine (Lys), consistent with the latitudinal gradient of AFS colonies and seasonal changes in seal foraging movement. The δ15N values of source AAs from Marion Island and Cape Shirreff were representative of particulate organic matter δ15N values in the Indian and southwest Atlantic sector, respectively, whereas more complex patterns were observed in the Atlantic sector around Bird Island. Variations in bulk δ15N values can also be attributed to changes in AFS diet, with females foraging in the Atlantic and Pacific targeting higher trophic level prey in winter. Trophic position estimation using Phe and leucine (Leu) suggested that females encompass more than 2 trophic levels. Our study highlights the utility of using Lys alongside Phe to assess seasonal and ocean basin-level variations in the isotopic baseline and Leu/Phe for AFS trophic position estimation

Structure et résilience des réseaux trophiques benthiques de l'Arctique canadien et de la mer des Tchouktches

RÉSUMÉ: Les changements climatiques actuels sont à l’origine de nombreuses modifications dans l’océan Arctique, telles qu’une augmentation de la température des eaux de surface, une augmentation des apports fluviaux, une réduction dans la couverture de glace de mer, des changements de composition des espèces ou des changements dans la phénologie et l’intensité de la production primaire. Ces changements pourraient être à l’origine de modifications dans la structure et le fonctionnement des réseaux trophiques benthiques. Il est nécessaire aujourd’hui de décrire la structure et la résilience de réseaux trophiques benthiques de ces régions pour évaluer l’impact des changements climatiques sur celles-ci. Cette étude a pour objectifs de décrire la structure et la résilience des réseaux trophiques benthiques de l’Arctique canadien (polynie des eaux du Nord, archipel canadien, golfe d’Amundsen, mer de Beaufort) et de la mer des Tchouktches par une approche isotopique, et d’évaluer l’importance des algues de glace pour ces réseaux trophiques, à l’aide du biomarqueur d’algues de glace IP25 (Ice Proxy 25). Pour atteindre ces deux objectifs, nous avons collecté des échantillons de matière particulaire en suspension, de sédiments de surface, et de faune benthique de juillet à octobre 2014, à bord du NGCC Amundsen. Les valeurs en δ13C mesurées dans les sédiments de la polynie des eaux du Nord, de l’archipel canadien et de la mer des Tchoukches, traduisent une origine marine de la matière organique. La mer de Beaufort et le golfe d’Amundsen sont quant à eux caractérisés par des apports terrigènes et des apports mixtes (terrigènes et marins) respectivement. Ces différences dans l’origine de matière organique se retrouvent dans les signatures isotopiques des organismes et dans la structure des réseaux trophiques : la mer de Beaufort se distingue des autres régions par des signatures appauvries en 13C chez les consommateurs et par de nombreux organismes avec de hauts niveaux trophiques. La faible séparation trophique et la forte redondance trophique suggèrent que la polynie des eaux du Nord et l’archipel canadien semblent être les régions avec la plus grande possibilité de résilience face à des changements environnementaux. Nous avons mis en évidence la présence du marqueur d’algue de glace IP25 chez les organismes appartenant à tous les niveaux trophiques. Les plus fortes concentrations en IP25 ont été retrouvées chez les déposivores de surface. Les algues de glace semblent être une source de xv nourriture importante pour les organismes de l’archipel canadien, où les plus fortes concentrations en biomarqueurs d’algues de glace ont été retrouvées (en particulier chez les déposivores et les prédateurs) et pour la polynie des eaux du Nord où les signatures en carbone des organismes indiquent une assimilation d’algues de glace. -- Mot(s) clé(s) en français : Benthos, structure trophique, résilience, algues de glace, biomarqueur IP25, isotopes stables, Arctique Canadien, Mer des Tchouktches. -- ABSTRACT: Ongoing climate change is causing rapid changes in the Arctic Ocean, such as higher water temperatures, increased fluvial run-off, reduced sea-ice cover, change in species composition, change in the timing and intensity of primary production. Those changes will give rise to severe ecosystem changes propagating in benthic food web through all trophic levels. There is a need to establish benthic food web structure and resilience baseline for future comparison and to understand the impact of climate change in those various benthic food-webs. We also need a thorough study of the role of ice algae for the benthic food webs on a large scale. The objectives of this study were to describe the structure and the resilience of the benthic food-web of the Canadian Arctic and the Chukchi Sea (North Water Polynya, Canadian Archipelago, Amundsen Gulf, Beaufort Sea, Chukchi Sea), using stable carbon and nitrogen isotope analyses and to evaluate the importance of sea-ice algae in the benthic food-web using the Sea ice biomarkerIP25 (“Ice Proxy 25”). To reach these objectives, we collected suspended particulate organic matter, surface sediments and zoobenthic samples from July to October 2014 aboard the CCGS Amundsen. Values in δ13C in the sediment were indicative of a marine origin of the organic matter in the North Water Polynya, Canadian Archipelago and the Chukchi Sea. The Beaufort Sea was characterized by terrestrial input, and the Amundsen Gulf was characterized by a mix between terrestrial and marine input. Those differences in the origin of organic matter were mirrored in consumer isotopic signatures in all the regions. The Beaufort Sea differed from the other regions regarding the trophic structure. The high trophic redundancy and the low trophic separation of the North Water Polynya and the Canadian Archipelago suggest those regions have the higher potential of resilience facing environmental changes. We highlight transfer of ice algae across the different trophic levels. The biomarker IP25 was detectable in all the trophic guilds, and the higher concentrations were found in the surface deposit feeder. Ice algae seem to be an important food source for the Canadian Archipelago food web, were the higher concentration in IP25 were found and for the North Water Polynya, where the carbon stable isotopic signatures indicate ice algae assimilation. -- Mot(s) clé(s) en anglais : Benthos, trophic structure, resilience, ice-algae, IP25 biomarker, stable isotopes, Canadian arctic, Chukchi Sea

Southern Ocean food-webs and climate change:A short review and future directions

Food-webs are a critical feature of ecosystems and help us understand how communities will respond to climate change. The Southern Ocean is facing rapid and accelerating changes due to climate change. Though having evolved in an isolated and somewhat extreme environment, Southern Ocean biodiversity and food-webs are among the most vulnerable. Here, we review 1) current knowledge on Southern Ocean food-webs; 2) methods to study food-webs; 3) assessment of current and future impacts of climate change on Southern Ocean food-webs; 4) knowledge gaps; and 5) the role of Early Career Researchers (ECRs) in future studies. Most knowledge on Southern Ocean food-webs come from the pelagic environment, both at macro- and microbial levels. Modelling and diet studies of individual species are major contributors to the food-web knowledge. These studies revealed a short food-web, predominantly sustained by Antarctic Krill (Euphausia superba). Additionally, alternative pathways exist, involving other krill species, fish, and squid, which play equally important roles in connecting primary producers with top predators. Advantages and disadvantages of several techniques used to study Southern Ocean food-webs were identified, from the classical analyses of stomach contents, scats, or boluses to the most recent approaches such as metabarcoding and trophic-biomarkers. Observations show that climate change can impact the food-web in different ways. As an example, changes to smaller phytoplankton species can lengthen the food-web, increasing assimilation losses and/or changing nutrient cycles. Future studies need to focus on the benthic-dominated food-webs and the benthopelagic coupling. Furthermore, research during the winter season and below the ice-shelves is needed as these areas may play a crucial role in the functioning of this ecosystem. ECRs can play a significant role in advancing the study of Southern Ocean food-webs due to their willingness for interdisciplinary collaboration and proficiency in employing various methodologies, contributing to the construction of high-resolution food-webs

Trophic ecology of epibenthic communities exposed to different sea-ice concentrations across the Canadian Arctic Ocean

Sea ice is one of the most critical environmental drivers shaping primary production and fluxes of organic inputs to benthic communities in the Arctic Ocean. Fluctuations in organic inputs influence ecological relationships, trophic cascades, and energy fluxes. However, changes in sea-ice concentration (SIC) induced by global warming could lead to significant shifts in trophic interactions, ultimately affecting the functioning of Arctic food webs. Despite the increasing concern over the need to understand benthic species and food web responses to rapid sea-ice loss, few studies have addressed this topic so far. Using multiple niche metrics based on stable isotopes, this research examined the trophic ecology of epibenthic communities in areas with different SIC across the Canadian Arctic Ocean. We found that trophic niches varied according to complex interactions between environmental conditions, resource supply, and biotic pressures such as predation and competition. Our results highlighted a lower isotopic richness (i.e., shorter food chain length and niche width) in low and high SIC areas, suggesting homogeneity of resources and a low diversity of food items ingested by individuals. In contrast, a higher isotopic richness (i.e., broad niche) was observed in the moderate SIC area, implying higher heterogeneity in basal food sources and consumers using individual trophic niches. Finally, our findings suggested a lower isotopic redundancy in areas with high SIC compared to low and moderate SIC. Overall, our results support the idea that sea ice is an important driver of benthic food web dynamics and reinforce the urgent need for further investigations of declining sea ice cover impacts on Arctic food web functioning

Illustration of Southern Ocean food-web different pathways.

Yellow arrows show the long standing short, krill-dominated pathway while red arrows show alternative, but equally important, pathways with other krill, fish, and squid as major links between primary producers and higher-level predators. Myctophid and toothfish drew by Tom Langbehn.</p

Southern Ocean and the Antarctic Polar Front (APF).

Full circles show locations where previous studies analysed the food-web (e.g. Fildes Bay); Empty circles show the location of general studies, i.e. studies analysing the food-web of an entire region (e.g. Ross Sea). Colour code shows the different types of food-webs. WAP: Western Antarctic Peninsula. Map was produced using QGis 3.20 Odense. Basemap is the “ESRI Ocean Basemap” [65].</p

Summary of the advantages and limitations of different methodologies used to study Southern Ocean food-webs.

Studies presented are examples of applying the different methodology to study the entire food-web, the diet and/or trophic ecology of Southern Ocean ecosystems and species (and in some cases from the Patagonian shelf).</p