Antarctic krill Euphausia superba: spatial distribution, abundance, and management of fisheries in a changing climate

Abstract

Antarctic krill Euphausia superba, a keystone species in the Southern Ocean, is highly relevant for studying effects of climate-related shifts on management systems. Krill provides a key link between primary producers and higher trophic levels and supports the largest regional fishery. Any major perturbation in the krill population would have severe ecological and economic ramifications. We review the literature to determine how climate change, in concert with other environmental changes, alters krill habitat, affects spatial distribution/abundance, and impacts fisheries management. Findings recently reported on the effects of climate change on krill distribution and abundance are inconsistent, however, raising questions regarding methods used to detect changes in density and biomass. One recent study reported a sharp decline in krill densities near their northern limit, accompanied by a poleward contraction in distribution in the Southwest Atlantic sector. Another recent study found no evidence of long-term decline in krill density or biomass and reported no evidence of a poleward shift in distribution. Moreover, with predicted decreases in phytoplankton production, vertical foraging migrations to the seabed may become more frequent, also impacting krill production and harvesting. Potentially cumulative impacts of climate change further compound the management challenge faced by CCAMLR, the organization responsible for conservation of Antarctic marine living resources: to detect changes in the abundance, distribution, and reproductive performance of krill and krill-dependent predator stocks and to respond to such change by adjusting its conservation measures. Based on CCAMLR reports and documents, we review the institutional framework, outline how climate change has been addressed within this organization, and examine the prospects for further advances toward ecosystem risk assessment and an adaptive management system.

Status, Change, and Futures of Zooplankton in the Southern Ocean

“…The importance of krill to the Southern Ocean ecosystem and as a fisheries resource is reflected in a number of dedicated reviews (Everson, 2000;Atkinson et al, 2012;Flores et al, 2012a;Hill et al, 2016;Siegel, 2016;Kawaguchi and Nicol, 2020;Meyer et al, 2020;McBride et al, 2021) and specific sections in more general reviews (Constable et al, 2014b;Hunt et al, 2016;Cavan et al, 2019;Saunders et al, 2019;Rogers et al, 2020;Cavanagh et al, 2021) which consider its population status and response to recent climate change. Despite this attention, current understanding is based on a limited suite of observations primarily from the Antarctic Peninsula and Scotia Sea regions (hereafter the southwest Atlantic), with the majority of sampling targeting the epipelagic zone (<200 m) (Atkinson et al, 2012).…”

“…For example, increased growth rates, feeding efficiency, habitat availability, population size and abundance, and range expansion of T. macrura, salps, and pteropods. A potential positive feedback loop, generated by the recovery of whale populations in the short term (see McBride et al, 2021), on phytoplankton productivity may also result in increased abundance of E. superba, E. crystallorophias, and T. macrura (Schmidt et al, 2011;Ratnarajah et al, 2014). For some species and localities, however, the positive effects of some drivers may be offset by the negative effects of other driversfor example, enhanced feeding efficiency of E. crystallorophias in response to increased diatoms in phytoplankton communities may not be sufficient to counteract the impacts of sea ice loss on spawning habitat and reproductive success.…”

“…There has also been progress in the understanding of the role of zooplankton in biogeochemical cycling, including the biological pump via grazing and vertical carbon flux (e.g., Alcaraz et al, 2014;Henschke et al, 2016;Belcher et al, 2019;Cavan et al, 2019;Manno et al, 2020) and their sensitivities to ocean acidification, including the additional synergistic effects of warming, temperature and deoxygenation (e.g., Kawaguchi et al, 2013;Manno et al, 2017Manno et al, , 2018Ericson et al, 2018;Peck et al, 2018;Bednaršek et al, 2019;Saba et al, 2021). Some of these advances, especially for Antarctic krill, are captured in other reviews, which have generally focused on the ecological effects of climate change (Mackey et al, 2012;Hunt et al, 2016;Chown and Brooks, 2019;Siegert et al, 2019;Rogers et al, 2020) and/or the Antarctic krill fishery (e.g., Meyer et al, 2020;McBride et al, 2021). This contribution adds to this literature with an up-to-date systematic comparison of the major Southern Ocean zooplankton taxa as detailed in the next paragraph.…”

Climate Change and Management of Antarctic Krill Fisheries

“…Some reports indicate that such a shift is already underway (Atkinson et al 2009;Hill et al 2019), although these findings have been disputed (Cox et al 2018(Cox et al , 2019. From what we know about krill biology, inter-species interaction and oceanographic conditions in the Southern Ocean, a poleward shift would most probably imply significant reduction of habitats suitable for krill spawning, hatching, larval survival and juvenile growth (McBride et al 2021).…”

Ocean climate connectivity and the future range shifts of marine biodiversity.

“…Indeed, species of great ecological significance in the Southern Hemisphere, such as Antarctic krill, are highly vulnerable to climate change and are forced to change their distributions 38 . Therefore, towards a climatic-smart conservation planning, information on species observations, potential responses, and climate redistribution patterns should be considered 39,40 .…”