Winter mortality in Calanus populations in two northern Norwegian fjords from 1984 to 2016

Espinasse, Boris; Tverberg, Vigdis; Kristensen, Jens Alexander; Skreslet, Stig; Eiane, Ketil

doi:10.1007/s00300-018-2294-5

Cited by 6 publications

(9 citation statements)

References 37 publications

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“…Thus, it would be difficult to use our abundance datasets to support a more thorough investigation of trophic interactions between the important Arctic species C. hyperboreus and other zooplankton, particularly since the taxonomic analysis of the two types of net samples was not necessarily done for the same stations in 2008. Nevertheless, results from a new study in Scandinavian fjords support our hypothesis that predation is a determinant factor of the Arctic Calanus populations loss in winter (Espinasse et al, 2018). This was most likely the case also for Metridia longa in Amundsen Gulf.…”

Section: Control Of Recruitmentsupporting

confidence: 63%

Could offspring predation offset the successful reproduction of the arctic copepod Calanus hyperboreus under reduced sea-ice cover conditions?

Darnis

Wold

Falk‐Petersen

et al. 2019

Progress in Oceanography

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Life cycle and reproduction of Calanus hyperboreus were studied during a year of record low ice cover in the southeastern Beaufort Sea. Stages CIV, adult females and CV dominated the overwintering population, suggesting a 2-to 3-year life cycle. Within two spring-summer months in the upper water column females filled their energy reserves before initiating their downward seasonal migration. From February to March, vigorous reproduction (20-65 eggs f −1 d −1) delivered numerous eggs (29 000 eggs m −2) at depth and nauplii N1-N3 (17 000 ind. m −2) in the water column. However, CI copepodite recruitment in May, coincident with the phytoplankton bloom, was modest in Amundsen Gulf compared to sites outside the gulf. Consequently, C. hyperboreus abundance and biomass stagnated throughout summer in Amundsen Gulf. As a mismatch between the first-feeding stages and food was unlikely under the favourable feeding conditions of April-May 2008, predation on the egg and larval stages in late winter presumably limited subsequent recruitment and population growth. Particularly abundant in Amundsen Gulf, the copepods Metridia longa and C. glacialis were likely important consumers of C. hyperboreus eggs and nauplii. With the ongoing climate-driven lengthening of the ice-free season, intensification of top-down control of C. hyperboreus recruitment by thriving populations of mesopelagic omnivores and carnivores like M. longa may counteract the potential benefits of increased primary production over the Arctic shelves margins for this key prey of pelagic fish, seabirds and the bowhead whale.

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Section: Control Of Recruitmentsupporting

confidence: 63%

Could offspring predation offset the successful reproduction of the arctic copepod Calanus hyperboreus under reduced sea-ice cover conditions?

Darnis

Wold

Falk‐Petersen

et al. 2019

Progress in Oceanography

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“…We aim to reflect general characteristics of seasonal dynamics along the latitudinal gradient, rather than local realism. We base our prey field on data available from the literature (Espinasse et al., 2018; Gislason et al., 2007; Gislason & Silva, 2012; Gluchowska, Dalpadado, et al., 2017; Gluchowska, Trudnowska, et al., 2017; Heath et al., 2000; Irigoien, 2000; Melle et al., 2004, 2014; Nöthig et al., 2015; Østvedt, 1955) (for localities see Figure 1a). Here, we consider copepods of 2.7 mm length, that is, CV‐CVI Calanus finmarchicus , CIV‐CV Calanus glaciale or CIII‐CV Calanus hyperboreus , as suitable prey for B. glaciale (Pepin, 2013).…”

Section: Methodsmentioning

confidence: 99%

Poleward distribution of mesopelagic fishes is constrained by seasonality in light

Langbehn

Aksnes

Kaartvedt

et al. 2021

Global Ecol Biogeogr

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Aim Mesopelagic fishes have a near‐global distribution in the upper 1,000 m from tropical to sub‐Arctic oceans across temperature regimes. Yet, their abundance decreases poleward and viable populations seem excluded from high latitudes. Why? Location North Atlantic between 50–85°N, with implications for high‐latitude oceans globally. Time period Present‐day. Major taxa studied Diel vertically migrating (DVM) mesopelagic fishes. Methods We use a mechanistic, state‐dependent life‐history model to characterize DVM mesopelagic fishes. This model links light‐dependent encounters and temperature‐dependent physiology, allowing optimal DVM strategies to emerge. We run the model along a latitudinal gradient with increasing seasonality in light and track individual fitness‐related measures, that is, survival and surplus energy, through the annual cycle to make predictions about population consequences. Results Mesopelagic fishes thrive in the oceans’ twilight zone, and many are dependent on periods of darkness for safe foraging near the surface, before migrating back to depth during daytime. When daylight lasts for 24 hr during the Arctic summer, these fish are trapped in deep waters void of prey because it is never safe to forage in the shallow waters where zooplankton prey are found. Hence, they are left with two poor options, starvation at depth or depredation while foraging. Our model predicts surplus energy, vital for reproduction and growth, to halve from 50–85°N and annual survival to drop by two‐thirds over a narrow range of 10° of latitude around the Arctic Circle. Thus, low recruitment and high predation mortality during summer make polar waters population sinks for mesopelagic fishes because of the extreme seasonality in light. Main conclusions At high latitudes, foraging mesopelagic fishes are exposed to sunlight in upper waters also at night. This makes them easy prey for visual predators, which limits their poleward distribution. Our findings highlight the importance to think beyond temperature to explain high‐latitude range limits.

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“…This shift is a result of the decreased stratification of the NCC caused by reduced freshwater discharge after summer and increased turbulence forced by winds during autumn (Haakstad 1977), while prevailing south-western winds in September and October accelerates the surface advection of NCC water towards the Norwegian coast and fjords in general (Aure et al 2007). However, Espinasse et al (2018) observed that the inflow frequency and residence time of the water qualities in Saltfjord and Mistfjord differ according to local winds that change on short temporal scales.…”

Section: Introductionmentioning

confidence: 99%

“…Many species establish local stocks by immigrating from extensive population systems in the Arctic Mediterranean (Tchernia 1980), where the ecosystem has been evolving since the first glaciation of the Pleistocene period (Dunbar 1968). The relative abundance of wintering stocks in fjords changes with the hemispheric climate by its effects on large-scale thermohaline circulation within the Arctic Mediterranean ecosystem, which eventually influences the local shelf-to-fjord advection of both oceanic NAC water and shelf water of lower salinity (Skreslet et al 2015;Espinasse et al 2018). Temporal changes in a fjord's abundance of wintering zooplankton are a balance between local mortality and the exchange of water with outside habitats.…”

Section: Introductionmentioning

confidence: 99%

“…In general, immigration of zooplankton from deep shelf habitats to sill fjords during winter is related to capacities for vertical migration and facilitated by upwelling caused by local katabatic winds (Skreslet & Loeng 1977) or by regional coastal upwelling that results from Ekman transport (Aure et al 2007;Espinasse et al 2018). Both processes lift dense shelf water residing outside the sill, which may lead to overflow into the fjord basin.…”

Section: Introductionmentioning

confidence: 99%

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Variable predator–prey relations in zooplankton overwintering in Subarctic fjords

Skreslet

Espinasse

Olsen

et al. 2020

POLAR

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Zooplankton predator–prey relations in northern Norwegian fjords are highly variable in time and space, and the mechanisms driving this variability are still poorly understood. Replicate Juday net sampling in October and February from 1983 to 2005, which included five repeated tows from bottom to surface, was conducted in Saltfjord and Mistfjord, northern Norway. The time-series provided evidence of in situ variability in species abundance, as well as seasonal and interannual changes in standing stock abundance. The shallow sill of one fjord caused accumulation of coastal water in the fjord’s basin, while the other fjord’s deeper sill selected denser water of Atlantic origin from the same open shelf habitat. The selective advection caused differences in the immigration of species recruiting to the fjords’ specific overwintering communities of zooplankton. Statistical analyses of the cumulated replicate data indicated significant in situ variability in the spatial density of species. Cases with an abundance of carnivores relating positively to other species probably resulted from the carnivores’ attraction to patches with concentrations of prey. Interspecific negative density relations likely indicated either predator avoidance or substantial trophic activity during the sampling. During years of high abundance, some wintering stocks of carnivores evidently reduced the local stocks of overwintering prey. We conclude that predator–prey interactions and stock variability in Subarctic fjords result from complex bio-geophysical interactions that occur on the scales of local habitats and basin-scale population systems.

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Winter mortality in Calanus populations in two northern Norwegian fjords from 1984 to 2016

Cited by 6 publications

References 37 publications

Could offspring predation offset the successful reproduction of the arctic copepod Calanus hyperboreus under reduced sea-ice cover conditions?

Could offspring predation offset the successful reproduction of the arctic copepod Calanus hyperboreus under reduced sea-ice cover conditions?

Poleward distribution of mesopelagic fishes is constrained by seasonality in light

Variable predator–prey relations in zooplankton overwintering in Subarctic fjords

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