Mesozooplankton community composition controls faecal pellet flux and remineralisation depth in the Southern Ocean

Zooplankton faecal pellets (FPs) are important conduits of carbon from the surface to the deep ocean, as shown by their presence in deep-sea sediment traps. Zooplankton themselves are thought to play an important role in the breakdown and reworking of FPs as they sink, whilst processes such as diel vertical migration (DVM) may enhance the supply of carbon to the mesopelagic. However, comparatively little is known about the processes or variability of FP sinking/ transport within the upper mesopelagic and how this relates to deeper ocean export. Profiles of FP type and size, and the contribution made by FPs to mesopelagic carbon flux to a depth of 400 m, were considered. Three contrasting locations in the Scotia Sea were compared, which together reflect the variability in physical regime and productivity encountered across the Southern Ocean. Comparing observed FPs with predictions from the mesozooplankton community, we show that, even at shallow depths, the smallest fraction of FP is under-represented, suggesting rapid remineralisation, incorporation into larger aggregates or reworking into larger FPs, and that the flux is dominated by FPs from larger zooplankton. In contrast to models where POC attenuation rates are set to increase with temperature, we find that FP carbon flux attenuates rapidly in low productivity, colder regions dominated by krill, while remineralisation is deeper in warmer areas where productivity is high and copepods dominate. This emphasises the strong modulation of the zooplankton community on the supply and transfer of FP carbon between the epi- and mesopelagic. Evidence was found to suggest that DVM enhances FP flux across the upper mesopelagic, producing a pulse of fresh, dense material that may support secondary production and heterotrophic respiration in the mesopelagic. This illustrates that variability in flux at short (daily) as well as longer (seasonal) timescales may have important implications for the supply of FP carbon to deeper waters

Plankton and nekton community structure in the vicinity of the South Sandwich Islands (Southern Ocean) and the influence of environmental factors

The South Sandwich Islands (SSI) are a biologically productive archipelago situated in the eastern Scotia Sea to the south of the eastward flowing Antarctic Circumpolar Current (ACC). The islands support important populations of higher predators, including several penguin species, seals and humpback whales. Despite this, the plankton ecology of the region has been little studied and information on mesoscale structure and environmental forcing of plankton ecology is particularly limited. We conducted a comprehensive oceanographic and net sampling campaign during the CCAMLR Area 48 Survey (January and February 2019), incorporating phytoplankton, mesozooplankton and macrozooplankton/nekton. Satellite chlorophyll-a (chl-a) data showed the development of a large bloom that was initiated two months prior to our study period at the south-eastern edge of the archipelago and propagated northwards along the eastern side, limited to the east by mesoscale features associated with the southern boundary of the ACC (SB). Multivariate cluster analysis revealed distinct mesoscale structure within the plankton community, with four spatially defined groups of phytoplankton and macrozooplankton/nekton, and three cluster groups of mesozooplankton. North of the SB, we found some spatial congruence between the three plankton assemblages, with a distinct, spatially coherent, cluster in each, corresponding to a warmer water community. Here, biomass was dominated by mesozooplankton, particularly calanoid copepods Rhincalanus gigas, Calanus propinquus, C. simillimus and Euchaetidae. The corresponding phytoplankton community was dominated by small diatoms, particularly Thalassionema spp., Pseudo-nitzschia spp., Fragilariopsis spp. and Chaetoceros spp., whilst Themisto gaudichaudii, Euphausia triacantha and myctophids were the major contributors to the macrozooplankton/nekton community. South of the SB, there was some spatial congruence between phytoplankton and macrozooplankton/nekton community structure on the western side of the archipelago, as well as on the eastern side that corresponded to the location of the bloom, but less association with mesozooplankton structure. Macrozooplankton/nekton structure was strongly driven by environmental conditions 1–2 months prior to the survey, including sea-ice distribution, surface phytoplankton concentration and productivity, whilst mesozooplankton was more tightly coupled to in-situ prevailing conditions such as surface temperature and integrated chl-a. Top-down pressure between trophic levels may have also had an influence on spatial patterns although direct evidence is lacking. Antarctic krill (Euphausia superba) was found with relatively low biomass at our net sampling sites (median biomass of 0.04 mg m−3 or <0.01 g m−2) while myctophids and the euphausiid Thysanoessa spp. predominated. We suggest that the highly productive and species rich pelagic community of the SSI supports multiple trophic pathways, and that off-shelf these may operate independently of Antarctic krill

Fair winds and following seas remotely: modifying perceptions of fieldwork as a requirement in marine science to aid in diversifying the discipline

Pursuing an academic career in marine science requires a range of skills that can be applied across different contexts, including experimental or computational proficiency, policy engagement, teaching, and seagoing fieldwork. The tendency to advertise careers in marine science with imagery of research expeditions results in the perception that it is a requirement for a career in marine science, an indicator of competitiveness in this discipline. Historically, those participating in remote fieldwork over extended periods of time were perceived as “adventurous explorers, with a strong bias towards western, able-bodied men” (Nash et al., 2019). Use of imagery reinforcing such notions for marine scientists fails to recognize that this perception can be discouraging to individuals from other backgrounds who may be excluded from the discipline by a range of real and perceived participatory barriers. Such exclusionary factors include: caring responsibilities, physical mobility, challenging social environments, isolating and physically uncomfortable working environments, mental health challenges, and access to opportunity (Giles et al., 2020). Such barriers disproportionately affect diverse, underrepresented, and marginalized groups, who may therefore struggle to identify with marine science as a potential discipline in which to pursue a successful career. Current work toward achieving net zero targets within ocean research emphasizes the use of autonomous vehicles as alternatives to ocean-going ships (Storey, 2023), and the proposed concept of digital twinning would incorporate similar remote technology coupled with simulations and shore-based decision-making. The concept of digital twinning refers to the use of responsive autonomous platforms that can both collect data and be operated in response to that data, which could provide a non-field-based approach to delivering marine science while also potentially expanding the opportunities available for individuals not able or interested in working in the field. In distinguishing digital twinning from current approaches such as data assimilating models, Kritzinger et al. (2018) note the importance of a two-way data flow between the physical environment and its virtual representation, called a “digital twin,” which, for example, may lead to changes in deployment strategy or data collection by researchers. Because these twins can be controlled and simulated anywhere with access to sufficient computing power, shore-based individuals can interact with a virtual version of the physical environment without being physically present at sea. The technology to support a fully realized digital twin of the ocean is still under development, but its use would require a broader range of skills and roles in the discipline, many of which are not accurately conveyed by the prevailing marketing of field-based disciplines (see Mol and Atchinson, 2019, regarding geosciences). In order to fully integrate this new approach into marine science, employment of individuals with experience and training across a wide range of disciplines from software engineering to traditional field sampling is essential while also presenting the potential for making marine science more inclusive. Individuals for whom working at sea is not possible and/or desirable would be able to make equally valid contributions to such research projects via digital routes, without facing the many barriers fieldwork may present. This study explores the expectations of marine scientists, from both early and more established career stages, around the importance of field experience as a precursor or requirement for a successful marine science career, and also examines the advantages and disadvantages of using digital twinning as a complement to traditional field-based marine science

Diel vertical migration of a Southern Ocean euphausiid, Euphausia triacantha, and its metabolic response to consequent short-term temperature changes

Diel vertical migration is a widespread behaviour amongst zooplankton, yet its effect on the rate at which individuals respire remains poorly understood. To address this, we investigated the effect of short-term temperature change on the respiration rate of Euphausia triacantha, a common component of the Southern Ocean zooplankton and a prominent vertical migrator. We found respiration to vary in response to size, with a value of 0.84 for the scaling coefficient, b. When scaled to b, respiration varied strongly in response to transitory temperature change, ranging from 0.37 to 1.65 µl O2 mg dry weight (DW)-b h-1 between 0.17 and 4.74°C, resulting in a Q10 of 3.6. This Q10 is higher than found by other studies examining the short-term respiration response of euphausiids, including those taking a multi-species perspective. This indicates that E. triacantha shows little compensation during short-term exposure to temperatures normally encountered during migration. Furthermore, it shows a distinct metabolic cost to diel vertical migration (DVM) when substantive changes in temperature are encountered over the course of the transit. This temporal variability in respiration rate has important implications for how community respiration is estimated, and for our understanding of DVM behaviour. Our results also have particular relevance to estimating the flux and sequestration of respiratory products, such as dissolved carbon dioxide, to and within the ocean interior

South Sandwich Islands – An understudied isolated Southern Ocean archipelago: Editorial

The South Sandwich Islands are an isolated, oceanic, volcanically formed archipelago in the Atlantic sector of the Southern Ocean. The complex bathymetry, coupled with the location in the marginal sea-ice zone and the relationship with the ACC makes the region both productive and biodiverse. Although remote, the region is not pristine and has been subject to historic exploitation of cetaceans and currently supports small, sustainably managed fisheries for two species of toothfish. This special issue brings together a suite of papers that further our knowledge of the region and will contribute to the next review of the South Georgia and South Sandwich Islands Marine Protected Area, which is due in 2023. The ten papers cover a broad range of subjects, adding to our knowledge of oceanography, pelagic and benthic ecology and of habitat use by mobile vertebrate predators such as cetaceans and penguins. Whilst the papers address some important knowledge gaps, they also highlight how little is known about this region and provide pointers to future research priorities

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

In the Southern Ocean, several zooplankton taxonomic groups, euphausiids, copepods, salps and pteropods, are notable because of their biomass and abundance and their roles in maintaining food webs and ecosystem structure and function, including the provision of globally important ecosystem services. These groups are consumers of microbes, primary and secondary producers, and are prey for fishes, cephalopods, seabirds, and marine mammals. In providing the link between microbes, primary production, and higher trophic levels these taxa influence energy flows, biological production and biomass, biogeochemical cycles, carbon flux and food web interactions thereby modulating the structure and functioning of ecosystems. Additionally, Antarctic krill (Euphausia superba) and various fish species are harvested by international fisheries. Global and local drivers of change are expected to affect the dynamics of key zooplankton species, which may have potentially profound and wide-ranging implications for Southern Ocean ecosystems and the services they provide. Here we assess the current understanding of the dominant metazoan zooplankton within the Southern Ocean, including Antarctic krill and other key euphausiid, copepod, salp and pteropod species. We provide a systematic overview of observed and potential future responses of these taxa to a changing Southern Ocean and the functional relationships by which drivers may impact them. To support future ecosystem assessments and conservation and management strategies, we also identify priorities for Southern Ocean zooplankton research

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

In the Southern Ocean, several zooplankton taxonomic groups, euphausiids, copepods, salps and pteropods, are notable because of their biomass and abundance and their roles in maintaining food webs and ecosystem structure and function, including the provision of globally important ecosystem services. These groups are consumers of microbes, primary and secondary producers, and are prey for fishes, cephalopods, seabirds, and marine mammals. In providing the link between microbes, primary production, and higher trophic levels these taxa influence energy flows, biological production and biomass, biogeochemical cycles, carbon flux and food web interactions thereby modulating the structure and functioning of ecosystems. Additionally, Antarctic krill (Euphausia superba) and various fish species are harvested by international fisheries. Global and local drivers of change are expected to affect the dynamics of key zooplankton species, which may have potentially profound and wide-ranging implications for Southern Ocean ecosystems and the services they provide. Here we assess the current understanding of the dominant metazoan zooplankton within the Southern Ocean, including Antarctic krill and other key euphausiid, copepod, salp and pteropod species. We provide a systematic overview of observed and potential future responses of these taxa to a changing Southern Ocean and the functional relationships by which drivers may impact them. To support future ecosystem assessments and conservation and management strategies, we also identify priorities for Southern Ocean zooplankton research

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

In the Southern Ocean, several zooplankton taxonomic groups, euphausiids, copepods, salps and pteropods, are notable because of their biomass and abundance and their roles in maintaining food webs and ecosystem structure and function, including the provision of globally important ecosystem services. These groups are consumers of microbes, primary and secondary producers, and are prey for fishes, cephalopods, seabirds, and marine mammals. In providing the link between microbes, primary production, and higher trophic levels these taxa influence energy flows, biological production and biomass, biogeochemical cycles, carbon flux and food web interactions thereby modulating the structure and functioning of ecosystems. Additionally, Antarctic krill (Euphausia superba) and various fish species are harvested by international fisheries. Global and local drivers of change are expected to affect the dynamics of key zooplankton species, which may have potentially profound and wide-ranging implications for Southern Ocean ecosystems and the services they provide. Here we assess the current understanding of the dominant metazoan zooplankton within the Southern Ocean, including Antarctic krill and other key euphausiid, copepod, salp and pteropod species. We provide an overview of observed and potential future responses of these taxa to a changing Southern Ocean and the functional relationships by which drivers may impact them. To support future ecosystem assessments and conservation and management strategies, we also identify priorities for Southern Ocean zooplankton research