Mesopelagic Sound Scattering Layers of the High Arctic: Seasonal Variations in Biomass, Species Assemblage, and Trophic Relationships

Geoffroy, Maxime; Daase, Malin; Cusa, Marine; Darnis, Gérald; Graeve, Martín; Hernández, Néstor Santana; Berge, Jørgen; Renaud, Paul E.; Cottier, Finlo; Falk‐Petersen, Stig

doi:10.3389/fmars.2019.00364

Cited by 45 publications

(38 citation statements)

References 80 publications

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“…In 2017, potential fish prey species were all more abundant in summer than in winter (Geoffroy et al, ), yet the rather consistent individual specialization on these prey predominantly in winter suggests that other mechanisms than prey availability may be at play, such as the impaired visual ability of fish prey to escape their predators during the winter months, though polar cod might be equally impaired visually.…”

Section: Discussionmentioning

confidence: 99%

“…Methot Isaac Kidd (MIK) sampling was performed both in Rijpfjorden in fall and in winter for an adjacent project but the samples were analyzed using different methods and levels of expertise. We therefore prefer to discuss our results by referring to past studies and other manuscripts, which have investigated the community composition and abundance of zooplankton in a range of fjords in Svalbard allowing us to make well‐informed inferences (Bandara et al, ; Błachowiak‐Samołyk et al, ; Cusa, ; Dalpadado et al, ; Geoffroy et al, ; Kraft, Berge, Varpe, & Falk‐Petersen, ). Furthermore, bioenergetic measurements of the potential prey would help elucidate whether, all else being equal, there is an advantage to select for a given prey over other available prey (But see Mayzaud & Boutoute, ).…”

Section: Discussionmentioning

confidence: 99%

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Seasonal shifts in feeding patterns: Individual and population realized specialization in a high Arctic fish

Cusa

Berge

Varpe

2019

Ecology and Evolution

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Species with a broad and flexible diet may be at an advantage in a rapidly changing environment such as in today's Arctic ecosystems. Polar cod (Boreogadus saida), an abundant and ecologically important circumpolar Arctic fish, is often described as a zooplankton generalist feeder, which suggests that it may cope successfully with changes in prey composition. This description is justified based on the relatively broad diet of polar cod across sites and seasons. In this case study, we used polar cod dietary data from fall and winter and from two distinct environments, dominated either by Arctic or Atlantic water masses in Svalbard. Our results point to the importance of time and space when drawing conclusions on dietary plasticity and degree of specialization. Polar cod diet differed significantly between fall and the winter and between Arctic and Atlantic domains. Polar cod from Arctic domains displayed a strong realized population specialization on Themisto libellula in fall, and the larger dietary niche width observed in the winter was the product of realized individual specialization, with increased feeding on fish prey. Overall, we did not observe a generalized feeding behavior. If dietary niche width is to inform conservation management, we argue it must be recognized that populations from a single species may adopt seasonally contrasting degrees of dietary specialization and that these populations may differ in their vulnerability to climate‐induced changes in prey community composition.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Seasonal shifts in feeding patterns: Individual and population realized specialization in a high Arctic fish

Cusa

Berge

Varpe

2019

Ecology and Evolution

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“…Peak densities and/or biomass coincided with waters above 0 • C (Crawford et al, 2012;Majewski et al, 2016), suggesting a possible role of this comparatively warm upper slope habitat from a thermal optimum perspective (Drost et al, 2014), in conjunction with zooplankton prey concentrations. On the Eurasian inflow slope, no comparable concentrations of B. saida have been reported, but several observations perhaps indirectly point to concentrations of B. saida abundance over Eurasian slopes: First, a mesopelagic layer encountering the seafloor at upper slope depths contains large zooplankton and a variety of fish species (250-600 m, Knutsen et al, 2017) includingand seasonally dominated by -B. saida (Geoffroy et al, 2019). And second, young Greenland halibut follow the continental slope and concentrate in the warmer (-0.6 to 1.2 • C) water layer between ∼400 and 780 m in St Anna and Voronin Troughs, where they actively feed on polar cod as their dominant prey (Dolgov and Benzik, 2017).…”

Section: Higher Trophic Level Biomass and Distributionmentioning

confidence: 99%

The Pan-Arctic Continental Slope: Sharp Gradients of Physical Processes Affect Pelagic and Benthic Ecosystems

et al. 2020

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Continental slopes – steep regions between the shelf break and abyssal ocean – play key roles in the climatology and ecology of the Arctic Ocean. Here, through review and synthesis, we find that the narrow slope regions contribute to ecosystem functioning disproportionately to the size of the habitat area (∼6% of total Arctic Ocean area). Driven by inflows of sub-Arctic waters and steered by topography, boundary currents transport boreal properties and particle loads from the Atlantic and Pacific Oceans along-slope, thus creating both along and cross-slope connectivity gradients in water mass properties and biomass. Drainage of dense, saline shelf water and material within these, and contributions of river and meltwater also shape the characteristics of the slope domain. These and other properties led us to distinguish upper and lower slope domains; the upper slope (shelf break to ∼800 m) is characterized by stronger currents, warmer sub-surface temperatures, and higher biomass across several trophic levels (especially near inflow areas). In contrast, the lower slope has slower-moving currents, is cooler, and exhibits lower vertical carbon flux and biomass. Distinct zonation of zooplankton, benthic and fish communities result from these differences. Slopes display varying levels of system connectivity: (1) along-slope through property and material transport in boundary currents, (2) cross-slope through upwelling of warm and nutrient rich water and down-welling of dense water and organic rich matter, and (3) vertically through shear and mixing. Slope dynamics also generate separating functions through (1) along-slope and across-slope fronts concentrating biological activity, and (2) vertical gradients in the water column and at the seafloor that maintain distinct physical structure and community turnover. At the upper slope, climatic change is manifested in sea-ice retreat, increased heat and mass transport by sub-Arctic inflows, surface warming, and altered vertical stratification, while the lower slope has yet to display evidence of change. Model projections suggest that ongoing physical changes will enhance primary production at the upper slope, with suspected enhancing effects for consumers. We recommend Pan-Arctic monitoring efforts of slopes given that many signals of climate change appear there first and are then transmitted along the slope domain.

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“…As a first order approximation, biomass of mesopelagic organisms should scale with energy input to the mesopelagic zone. However, research on mesopelagic macrozooplankton and micronekton has mainly focused on low-or mid-latitude systems 19,20 and knowledge of their vertical structure and effect on carbon fluxes at high latitudes remains scarce [21][22][23][24][25] . Scientific echosounders are frequently used to map mesopelagic deep-scattering layers (DSL).…”

Section: Main Textmentioning

confidence: 99%

The transformation of mesopelagic structure across polar fronts

Chawarski¹,

Klevjer²,

Côté³

et al. 2021

Preprint

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The oceans sequester 31% of atmospheric carbon annually 1, but the magnitude of biologically enhanced sequestration is not evenly distributed across the globe 2. Measuring surface primary productivity offers a reasonable proxy for estimating carbon flux into the ocean 3 but entirely misses the processes that affect carbon export to sequestration depths. A high proportion of carbon flux is broken up 4 or respired 5 by organisms at mesopelagic depths (200-1000 m). At low and mid-latitudes, daytime biomass peaks of mesopelagic organisms are clearly present and detectable as sound-scattering layers, and up to 40% of oceanic carbon passes through these layers 6,7. Here we demonstrate that acoustic backscatter, a proxy for abundance of mesopelagic fish and zooplankton decreases by up to 97% across polar fronts, revealing a distinct pelagic structure in high latitude systems. As mesopelagic fish and macrozooplankton comprise a large component of active carbon transport in the upper ocean, this latitudinal reduction in mesopelagic biomass across thermal fronts, in both the Arctic and Antarctic, suggests different carbon flux attenuation schemes exists in ocean twilight zones of polar ecosystem compared to low latitude systems. Rapid ocean warming projected at mesopelagic depths8 will likely disrupt vertical connectivity and alter biogeochemical cycles at high latitudes.

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Mesopelagic Sound Scattering Layers of the High Arctic: Seasonal Variations in Biomass, Species Assemblage, and Trophic Relationships

Cited by 45 publications

References 80 publications

Seasonal shifts in feeding patterns: Individual and population realized specialization in a high Arctic fish

Seasonal shifts in feeding patterns: Individual and population realized specialization in a high Arctic fish

The Pan-Arctic Continental Slope: Sharp Gradients of Physical Processes Affect Pelagic and Benthic Ecosystems

The transformation of mesopelagic structure across polar fronts

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