The importance of Antarctic krill in biogeochemical cycles

Abstract

Antarctic krill (Euphausia superba) are swarming, oceanic crustaceans, up to two inches long, and best known as prey for whales and penguinsbut they have another important role. With their large size, high biomass and daily vertical migrations they transport and transform essential nutrients, stimulate primary productivity and influence the carbon sink. Antarctic krill are also fished by the Southern Ocean's largest fishery. Yet how krill fishing impacts nutrient fertilisation and the carbon sink in the Southern Ocean is poorly understood. Our synthesis shows fishery management should consider the influential biogeochemical role of both adult and larval Antarctic krill. O cean biogeochemical cycles are paramount in regulating atmospheric carbon dioxide (CO 2) levels and in governing the nutrients available for phytoplankton growth 1. As phytoplankton are essential in most marine food webs, biogeochemistry is also important in fuelling fishery production 2. The role of phytoplankton in atmospheric CO 2 drawdown and fish production has been the central focus of many biogeochemical studies (e.g., refs. 3,4). However, despite evidence of their potential importance, higher organisms (metazoa) such as zooplankton (e.g., copepods and salps), nekton (e.g., adult krill and fish), seabirds and mammals 5-12 , have received less attention concerning their roles in the global biogeochemical cycles. One of the main mechanisms by which metazoa can influence biogeochemical cycles is through the biological pump 1 (Fig. 1). The biological pump describes a suite of biological processes that ultimately sequester atmospheric CO 2 into the deep ocean on long timescales. During photosynthesis in the surface, ocean phytoplankton produce organic matter and a fraction (< 40 %) sinks to deeper waters 13. It is estimated that 5-12 Gt C is exported from the global surface ocean annually 14 , with herbivorous metazoa contributing to the biological pump by releasing fast-sinking faecal pellets, respiring carbon at depth originally assimilated in the surface ocean and by excreting nutrients near the surface promoting further phytoplankton

Overcoming the Obstacles Faced by Early Career Researchers in Marine Science: Lessons From the Marine Ecosystem Assessment for the Southern Ocean

“…• Co-hosted an ECR workshop with APECS • An ECR led Pew funded project resulting in a Nature publication (Cavan et al, 2019) • • Create and support co-authorship opportunities (In, RC)…”

“…ECRs were involved in the conference planning, organisation and running • Conference registration fee waived for ECR organisers and prize winners • Co-hosted an ECR workshop with APECS • An ECR led Pew funded project resulting in a Nature publication(Cavan et al 2019) …”

“…Remote attendance was offered for the 2019 United Kingdom workshop ECRs were involved in the conference planning, organisation and running • Conference registration fee waived for ECR organisers and prize winners • Co-hosted an ECR workshop with APECS • An ECR led Pew funded project resulting in a Nature publication (Cavan et al 2019) ECRs were involved in the conference planning, organisation and running • Conference registration fee waived for ECR organisers and prize winners • Co-hosted an ECR workshop with APECS • An ECR led Pew funded project resulting in a Nature publication(Cavan et al 2019) …”

Commercial fishery disturbance of the global open-ocean carbon sink

“…As groundfish reside near the seabed, the pellets they egest would be subjected to less water column degradation prior to sedimentation of the carbon. Similarly, mesopelagic fish that live permanently or migrate daily into this depth realm can increase the sink of carbon to the deep sea and seabed 11 ; any carbon they release below the permanent thermocline (winter mixed layer depth) will not be subject to water column mixing and remain sequestered for decades or centuries 10 . Thus targeted or incidental harvesting of mesopelagic species is likely to increase the rate at which CO2 returns to the atmosphere (Fig.…”

“…mackerel or krill that feed seabirds), (9) killing predators (e.g. seabirds) that may otherwise fertilise the oceans but also help to maintain a balanced food web, and finally (10) the release discards which could cause localized dead zones.…”