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With rapid, sector-specific climatic changes impacting the Southern Ocean, we need circumpolar-scale biomass data of its plankton taxa to improve food web models, blue carbon budgets and resource management. Here, we provide a new dataset on mesozooplankton biomass with 2909 records spanning the last 90 yr, and describe, in comparable carbon units, their circumpolar distribution alongside those of phytoplankton, Antarctic krill, and salps. With our datasets, we estimate total summer carbon biomasses for phytoplankton (36 MT), mesozooplankton (67 MT), krill (30 MT), and salps (1.7 MT). The mesozooplankton value is much higher than previously reported and, added to that of krill and salps, points to an enormous overall biomass of zooplankton in the Southern Ocean. This means that the pyramids of biomass are often inverted, with higher biomass of zooplankton than of phytoplankton. Such high biomasses suggest key roles of grazers in nutrient cycling and we estimate an export of ~ 50 Mt C yr−1, solely from mortality of overwintering zooplankton that typically reside at depth. Deep lipid respiration (the lipid pump), for example, would increase this export even further. While inverted biomass pyramids prevailed at mid latitudes (50°–70°S), the balance of taxa differed regionally: for example, with biomass dominance by phytoplankton (highest latitudes and Pacific sector), mesozooplankton (Kerguelen Plateau), krill (north and east Scotia Sea), and salps (Crozet area). In light of contrasting climate change impacts between these sectors, we provide data that will underpin biogeochemical and food web models, blue carbon budgets, and the planning of marine protected areas.

Poleward range shifts are a global-scale response to warming, but these vary greatly among taxa and are hard to predict for individual species, localized regions or over shorter (years to decadal) timescales. Moving poleward might be easier in the Arctic than in the Southern Ocean, where evidence for range shifts is sparse and contradictory. Here, we compiled a database of larval Antarctic krill, Euphausia superba and, together with an adult database, it showed how their range shift is out of step with the pace of warming. During a 70-year period of rapid warming (1920s–1990s), distribution centres of both larvae and adults in the SW Atlantic sector remained fixed, despite warming by 0.5–1.0°C and losing sea ice. This was followed by a hiatus in surface warming and ice loss, yet during this period the distributions of krill life stages shifted greatly, by ~1000 km, to the south-west. Understanding the mechanism of such step changes is essential, since they herald system reorganizations that are hard to predict with current modelling approaches. We propose that the abrupt shift was driven by climatic controls acting on localized recruitment hotspots, superimposed on thermal niche conservatism. During the warming hiatus, the Southern Annular Mode index continued to become increasingly positive and, likely through reduced feeding success for larvae, this led to a precipitous decline in recruitment from the main reproduction hotspot along the southern Scotia Arc. This cut replenishment to the northern portion of the krill stock, as evidenced by declining density and swarm frequency. Concomitantly, a new, southern reproduction area developed after the 1990s, reinforcing the range shift despite the lack of surface warming. New spawning hotspots may provide the stepping stones needed for range shifts into polar regions, so planning of climate-ready marine protected areas should include these key areas of future habitat.

Marine ecosystems on continental shelves face multiple challenges due to anthropogenic disturbances, many of which can change the seawater stoichiometry (C:N:P) and consequently elemental ratios of phytoplankton. This change in food quality may not be tolerated by all grazers and predators. Gelatinous and soft-bodied zooplankton (GZ) might be more resilient to such changes. We sampled GZ species in neritic and oceanic waters of the Northeast Pacific off British Columbia, Canada, determined their phosphorus (P) content and elemental ratios (C/P, N/P), and analysed intraspecific variability associated with size and ontogeny. P content was measured for twelve GZ taxa. P % DW (dry weight) decreased with size for the hydrozoan Aequorea sp., scyphozoans Aurelia labiata, Cyanea capillata, and the thaliacean Salpa aspera, and differed significantly for two development stages of the salp S. aspera. While C/P and N/P were mostly size and stage independent, they were highly variable. C/P values of GZ were generally higher than values of crustacean zooplankton, indicating that GZ represent poor-quality prey for non-GZ predators, and that GZ may have a higher resilience towards P-limited (low quality) prey. Changing ocean conditions and nutrient stoichiometry of prey may favour GZ, although large variability in P dynamics among GZ taxa and uncertainty about future ocean stoichiometry changes make generalisations difficult.

The freshwater hydrozoan Craspedacusta sowerbii was introduced to habitats around the world and they spread into the surrounding water bodies thereafter. Despite an increase in reported observations, little is known about its genetics, physiology and ecology. The present study examined the organic content, elemental composition and energy content of jellyfish collected in Canada and the USA and compared these metrics with their marine counterparts and other co-occurring zooplankton. Specimens from the sampled lakes were sexed and molecularly characterized. Molecular, stoichiometric and energetic information is critical in determining distribution pathways and trophic connections. Molecular analyses showed two closely related sequences in North America, one shared by the Canadian and Japanese specimens, while another one is widely present across the Americas. Organic and all elemental contents were higher compared to marine jellyfish species. Estimated energy content of C. sowerbii was 20–27 kJ g DW−1, which is 2-fold higher than for marine hydrozoans and compared well with cladocerans, copepods and rotifers. Estimated C/P values indicated that cladocerans and copepods are suitable prey for C. sowerbii and that jellyfish may compete with juvenile fish to fulfill similar nutrient demands. Freshwater jellyfish were stoichiometrically and energetically different from marine hydrozoans, indicating higher importance in freshwater food webs than previously thought.

Over the past decades, two key grazers in the Southern Ocean (SO), krill and salps, have experienced drastic changes in their distribution and abundance, leading to increasing overlap of their habitats. Both species occupy different ecological niches and long-term shifts in their distributions are expected to have cascading effects on the SO ecosystem. However, studies directly comparing krill and salps are lacking. Here, we provide a direct comparison of the diet and fecal pellet composition of krill and salps using 18S metabarcoding and fatty acid markers. Neither species’ diet reflected the composition of the plankton community, suggesting that in contrast to the accepted paradigm, not only krill but also salps are selective feeders. Moreover, we found that krill and salps had broadly similar diets, potentially enhancing the competition between both species. This could be augmented by salps’ ability to rapidly reproduce in favorable conditions, posing further risks to krill populations.

Pacific herring (Clupea pallasii) plays an important and multifaceted role in the Northeast Pacific as a forage fish in coastal ecosystems, target species for commercial fisheries, and culturally significant subsistence resource for coastal communities. This study comparatively evaluated herring fisheries management strategy performance relative to ecological and socioeconomic objectives. Management strategy evaluation employed a mass-balanced ecosystem operating model and accounted for parameter uncertainty, stock assessment error, and strategy implementation error through Monte Carlo resampling. Results revealed a notable trade-off between stable herring catches and high biomasses of herring and several predators. Herring biomass control point values influenced this trade-off more than harvest control rule form. All British Columbia and Alaska strategies yielded similar ecological and socioeconomic impacts relative to the unfished herring baseline. Precautionary strategies recommended for forage fish combined high ecosystem benefits and socioeconomic costs. Reducing fishing mortality fourfold within an existing strategy suggested a possible compromise solution to this trade-off. However, ecological impacts of all strategies were sensitive to operating model parameter uncertainty, stock assessment error, and strategy implementation error, with the potential for undesirable ecosystem states across all strategies. This study suggests trade-offs among management objectives should be considered in pursuing ecosystem-based fisheries management for forage fish.

Normalized biomass size spectra (NBSS) are frequently used to describe pelagic communities. However, the underlying structure of NBSS may lead to varying intercepts and slopes when only a portion of the biomass range is sampled. This may be further perpetuated by the sampling efficiency of different gears/mesh sizes. Spatial and seasonal effects of mesh size on zooplankton NBSS and production were evaluated. Zooplankton were collected during winter, spring and summer (2017–2019) between Vancouver Island and Station Papa (50°N, 145°W) using a 64-μm Working Party 2 (WP-2) net and a 236-μm bongo net and analyzed using a bench-top laser optic particle counter. WP-2 and bongo NBSS overlapped in 11 size classes, for which the WP-2 more effectively sampled smaller size classes and converged with the bongo in larger size classes. Differences in NBSS slopes from the two nets were detected, yet no differences in total production. However, the contribution of individual size classes to total production varied spatially and seasonally. Total production in the coastal region exhibited strong seasonal variability. Notably, summer estimates of production in the coastal region were at least 2-fold higher than transitional and open ocean regions. This study suggests that using one mesh size may underestimate zooplankton NBSS and thus production.

Gelatinous and soft-bodied zooplankton (GZ) have long been considered to have low energetic value (‘trophic dead end hypothesis’) and be insufficient to sustain higher trophic levels. However, the nutritional composition and energy content of GZ are often poorly known for entire groups, ignoring species-, size-, and stage-specific differences. In this study, organic matter and elemental composition (carbon and nitrogen) were measured for >1000 specimens from 34 GZ species collected from neritic and oceanic waters of the Northeast Pacific between 2014 and 2020. Species included 3 gastropods, 16 hydrozoans, 2 nude ctenophores, 6 scyphozoans, 3 tentaculate ctenophores, and 4 thaliaceans. Organic content and elemental composition were used to estimate energy content using published conversion factors and differed between and within taxonomic classes. Size-dependent variability was shown for several species. Differences in organic content and elemental composition by development stage were observed in a salp and scyphomedusa species, highlighting the need to consider life cycle stages separately. The relative energy values of GZ were generally low and highly variable, although some taxa were comparable to crustaceans. The findings of the present study emphasise the need for a more detailed consideration of GZ in marine food web models and time series analyses, to take into account their inter- and intraspecific variability.

Stable isotope analysis was used to determine the relative dietary importance of kelp-derived detritus to plankton and benthic organisms along a gradient of kelp abundance driven by recovering sea otter populations along the west coast of Vancouver Island (WCVI), Canada. The study used region-specific kelp isotope values (δ13C and δ15N) and season-specific phytoplankton isotope values to model dietary contributions of kelp-derived detritus (KDD). In general, KDD contributions were moderate to high in most plankton size fractions during the summer and decreased during the winter, particularly in the kelp sparse region. Hypothesized regional and spatial (distance from the coast) differences in kelp detritus contributions to zooplankton were not evident. Modeled estimates of the KDD contribution to benthic invertebrates were high (>40%) and independent of the organism size, among regions and between seasons, with the exception of Astraea gibberosa in the kelp abundant region. Local oceanography, natural kelp isotope signature variation, and significant overlap between kelps’ and blooming phytoplankton isotope values led to a large uncertainty in the assessed KDD contributions in benthic organisms. These results highlighted the importance of the KDD as a widespread and stable year-round food source in coastal kelp populated regions.

Zooplankton production estimates are necessary to understand the availability and transfer of energy to higher trophic levels in marine food webs. Methods have been developed to quantify zooplankton production; however, they are difficult to compare as they focus on single species, groups, stages, or size classes of zooplankton. We compared 2 methods for estimating crustacean production: the chitobiase method (based on a crustacean moulting enzyme), and 3 empirical growth rate models (Huntley-Lopez, Hirst-Lampitt, and Hirst-Bunker) applied to optically resolved mesozooplankton normalized biomass size spectra (NBSS). Mesozooplankton net samples were collected between March and August of 2010 and 2011 in Saanich Inlet (British Columbia, Canada) and analyzed in the laboratory using microscopy and a bench-top laser optical particle counter (lab-LOPC). Microscope and lab-LOPC estimates of abundance and biomass were in close agreement. Crustacean production estimates were highest using Huntley-Lopez (0.20-185.3 mg C m-3 d-1), followed by Hirst-Bunker (0 .01-18.3 mg C m-3 d-1), chitobiase (0.05-15.6 mg C m-3 d-1), and Hirst-Lampitt (0.03-14.3 mg C m-3 d-1). Hirst-Lampitt-, Hirst-Bunker-, and chitobiase-based estimates of crustacean production and trophic transfer efficiency (TTE) yielded similar patterns/magnitude, while the Huntley-Lopez model was more variable. Estimates showed stronger agreement in 2011 than in 2010, attributed to the shift from El Niño to La Niña conditions. We highlight similarities/differences associated with these techniques and suggest that Hirst-Bunker estimates of production and TTE are most consistent with chitobiase-based values.

The stock‐specific distribution of maturing salmon in the North Pacific has been a persistent information gap that has prevented us from determining the ocean conditions experienced by individual stocks. This continues to impede understanding of the role of ocean conditions in stock‐specific population dynamics. We assessed scale archives for 17 sockeye salmon (Oncorhynchus nerka) stocks covering the entire North Pacific, from the Columbia River (Washington State and British Columbia) to Kamchatka Peninsula (Russia), to infer salmon locations during their last growing season before returning to their spawning grounds. The approach used, first pioneered in salmon stocks in the Atlantic, relies on the relationship between temporal changes in δ13C in salmon scales and sea surface temperature to estimate salmon distribution based on correlation strength. An advantage of this approach is that it does not require fish sampling at sea, but relies on existing fishery agency collections of salmon scales. Significant correlations were found for 7 of the stocks allowing us to propose plausible feeding grounds. Complementary information from δ15N, historical tagging studies, and connectivity analysis were used to further refine distribution estimates. This study is a first step toward estimating stock‐specific distributions of salmon in the North Pacific and provides a basis for the application of the approach to other salmon scale archives. This information has the potential to improve our ability to relate stock dynamics to ocean conditions, ultimately enabling improved stock management. For example, our estimated distributions of Bristol Bay and NE Pacific stocks demonstrated that they occupy different areas with a number of the former being distributed in the high productivity shelf waters of the Aleutian Islands and Bering Sea. This may explain why these stocks seem to have responded differently to changes in ocean conditions, and the long‐term trend of increased productivity of Bristol Bay sockeye., Stock‐specific salmon high seas distribution is largely unknown. We used the correlation between sea temperature and stable isotope ratio in scales of 17 salmon stocks to estimate their distributions during their last year at sea. This has resulted in a better comprehension of salmon migration routes, differences in stock productivity trends over large areas (e.g., Bristol Bay vs Northeast Pacific) and differences in productivity of stocks with geographically close spawning grounds.

The North Pacific Marine Salmon Diet Database is an open-access relational database built to centralize and make accessible salmon diet data through a standardized database structure. The initial data contribution contains 21,862 observations of salmon diet, and associated salmon biological parameters, prey biological parameters, and environmental data from the North Pacific Ocean. The data come from 907 unique spatial areas and mostly fall within two time periods, 1959–1969 and 1987–1997, during which there are more data available compared to other time periods. Data were extracted from 62 sources identified through a systematic literature review, targeting peer-reviewed and gray literature. The purpose of this database is to consolidate data into a common format to address gaps in our ecological understanding of the North Pacific Ocean, particularly with respect to salmon. This database can be used to address a variety of questions regarding salmon foraging, productivity, and marine survival. The North Pacific Marine Salmon Diet Database will continue to grow in the future as more data are digitized and become available., Measurement(s) Gastric Content • diet Technology Type(s) digital curation • microscopy Factor Type(s) predator capture method • year of data collection • longitude • latitude • predator life stage • predator lowest taxonomic level • predator characteristics • predator replicates • type of diet data • prey life stage • prey lowest taxonomic level • prey characteristics Sample Characteristic - Organism Oncorhynchus mykiss • Oncorhynchus kisutch • Oncorhynchus tshawytscha • Oncorhynchus nerka • Oncorhynchus keta • Oncorhynchus gorbuscha Sample Characteristic - Environment ocean Sample Characteristic - Location North Pacific Ocean Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12981989

What limits secondary production in the estuaries of snowmelt-dominated basins? Due to substantial differences in their annual hydrographs, zooplankton dynamics in these estuaries are expected to differ from better-studied pluvial systems. We hypothesized that water residence time limited zooplankton production in the undammed, snowmelt-dominated estuary of the Fraser River, Canada. We sampled zooplankton and associated environmental variables bi-weekly to monthly in slough and channel areas of the estuary over a 33-month period. Annual mean copepod abundance at channel stations was low (2005 ± 238 ind. m−3) in comparison to other studied estuaries, with minima occurring during spring, concurrent with the freshet. Higher abundances (11,905 ± 3606 ind. m−3) observed at slough stations were attributed to estuarine copepods. Differences in abundance and species composition between slough and channel areas, and the coincidence of seasonal minima with the freshet, suggest that the low water residence time of this system limits zooplankton density and production. Heavy channelization of the Fraser River Estuary has further reduced water residence time in the estuary, likely affecting prey availability to fish and invertebrate predators. Given that peak river discharge in snowmelt-dominated basins occurs during the relatively short spring-summer growing season, the impacts of channelization on zooplankton production in the estuaries of snowmelt-dominated basins may be greater than in river-dominated estuaries subjected to different flow regimes.

In this article, we analyze the impacts of climate change on Antarctic marine ecosystems. Observations demonstrate large-scale changes in the physical variables and circulation of the Southern Ocean driven by warming, stratospheric ozone depletion, and a positive Southern Annular Mode. Alterations in the physical environment are driving change through all levels of Antarctic marine food webs, which differ regionally. The distributions of key species, such as Antarctic krill, are also changing. Differential responses among predators reflect differences in species ecology. The impacts of climate change on Antarctic biodiversity will likely vary for different communities and depend on species range. Coastal communities and those of sub-Antarctic islands, especially range-restricted endemic communities, will likely suffer the greatest negative consequences of climate change. Simultaneously, ecosystem services in the Southern Ocean will likely increase. Such decoupling of ecosystem services and endemic species will require consideration in the management of human activities such as fishing in Antarctic marine ecosystems. Expected final online publication date for the Annual Review of Marine Science Volume 12 is January 3, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

International audience; Mesopelagic communities are characterized by a large biomass of diverse macrozooplankton and micronekton (MM) performing diel vertical migration (DVM) connecting the surface to the deeper ocean and contributing to biogeochemical fluxes. In the Southern Ocean, a prominent High Nutrient Low Chlorophyll (HNLC) and low carbon export region, the contribution of MM to the vertical carbon flux of the biological pump remains largely unknown. Furthermore, few studies have investigated MM communities and vertical flux in naturally iron fertilized areas associated with shallow bathymetry. In this study, we assessed the MM community diversity, abundance and biomass in the Kerguelen Island region, including two stations in the HNLC region upstream of the islands, and two stations in naturally iron fertilized areas, one on the Plateau, and one downstream of the Plateau. The MM community was examined using a combination of trawl sampling and acoustic measurements at 18 and 38 kHz from the surface to 800 m. A conspicuous three-layer vertical system was observed in all areas - a shallow scattering layer, SSL, between 10 and 200 m; mid-depth scattering layer, MSL, between 200 and 500 m; deep scattering layer, DSL, between 500 and 800 m - but communities differing among stations. While salps (Salpa thompsoni) dominated the biomass at the productive Kerguelen Plateau and the downstream station, they were scarce in the HNLC upstream area. In addition, crustaceans (mainly Euphausia vallentini and Themisto gaudichaudii) were particularly abundant over the Plateau, representing a large, although varying, carbon stock in the 0–500 m water layer. Mesopelagic fish were prominent below 400 m where they formed permanent or migrant layers accounting for the main source of carbon biomass. Through these spatial and temporal sources of variability, complex patterns of the MM vertical distribution and associated carbon content were identified. The total carbon flux mediated by migratory myctophids at the four stations was quantified. While this flux was likely underestimated, this study identified the main components and mechanisms of active carbon export in the region and how they are modulated by complex topography and land mass effects.

Following a brief review of their biology, this contribution is an attempt to provide a global overview of the catches of mesopelagic fishes (of which 2.68 million tonnes were officially reported to the FAO) throughout the world ocean from 1950 to 2018, to serve as a baseline to a future development of these fisheries. The overview is based on a thorough scanning of the literature dealing with commercial or experimental fisheries for mesopelagics and their catches, and/or the mesopelagic bycatch of other fisheries. All commercial (industrial and artisanal) fisheries for mesopelagic fishes were included, as well as experimental fisheries of which we were aware, while catches performed only to obtain scientific samples were omitted. The processes of generating bycatch and causing discards are discussed, with emphasis on Russian fisheries. From peer-reviewed and gray literature, we lifted information on mesopelagic fisheries and assembled it into one document, which we then summarized into two text tables with catch data, one by country/region, the other by species or species groups.

Polar marine ecosystems are particularly vulnerable to the effects of climate change. Warming temperatures, freshening seawater, and disruption to sea-ice formation potentially all have cascading effects on food webs. New approaches are needed to better understand spatiotemporal interactions among biogeochemical processes at the base of Southern Ocean food webs. In marine systems, isoscapes (models of the spatial variation in the stable isotopic composition) of carbon and nitrogen have proven useful in identifying spatial variation in a range of biogeochemical processes, such as nutrient utilization by phytoplankton. Isoscapes provide a baseline for interpreting stable isotope compositions of higher trophic level animals in movement, migration, and diet research. Here, we produce carbon and nitrogen isoscapes across the entire Southern Ocean (>40°S) using surface particulate organic matter isotope data, collected over the past 50 years. We use Integrated Nested Laplace Approximation-based approaches to predict mean annual isoscapes and four seasonal isoscapes using a suite of environmental data as predictor variables. Clear spatial gradients in δ13C and δ15N values were predicted across the Southern Ocean, consistent with previous statistical and mechanistic views of isotopic variability in this region. We identify strong seasonal variability in both carbon and nitrogen isoscapes, with key implications for the use of static or annual average isoscape baselines in animal studies attempting to document seasonal migratory or foraging behaviors.

The high seas phase of Pacific salmon life history remains particularly data-limited, and the potential implications of climate impacts on ocean productivity for salmon condition and reproductive success is poorly understood. We used carbon and nitrogen stable isotopes (SI) from salmon scales to reconstruct aspects of the marine environment experienced by Rivers Inlet sockeye salmon (Oncorhynchus nerka) over the last century (1915–2016). Time series of SI compositions of salmon scales showed a greater variability after 1950, probably linked to more dynamic high seas environmental conditions. However, climate indices (e.g., Pacific Decadal Oscillation, El Niño Southern Oscillation) did not explain the SI variability. We assessed the time series with respect to changes in food web dynamics, including shifting trophic baselines, changes in prey–salmon diet, and changes in salmon foraging location. A significant correlation (r = 0.53) between sea surface temperature and δ13C enabled us to define the area of potential salmon distribution in the open ocean for approximately 9 months prior to sampling. This method shows high potential for stock-specific high seas distribution mapping that could be combined with prey isotope values to inform stock-specific foraging experience.

Pyrosomes are efficient grazers that can form dense aggregations. Their clearance rates are among the highest of any zooplankton grazer, and they can rapidly repackage what they consume into thousands of fecal pellets per hour. In recent years, pyrosome swarms have been found outside of their natural geographical range; however, environmental drivers that promote these swarms are still unknown. During the austral spring of 2017 a Pyrosoma atlanticum swarm was sampled in the Tasman Sea. Depth‐stratified sampling during the day and night was used to examine the spatial and vertical distribution of P. atlanticum across three eddies. Respiration rate experiments were performed onboard to determine minimum feeding requirements for the pyrosome population. P. atlanticum was 2 orders of magnitude more abundant in the cold core eddy (CCE) compared to both warm core eddies, with maximum biomass of 360 mg WW·m−3, most likely driven by high chlorophyll a concentrations. P. atlanticum exhibited diel vertical migration and migrated to a maximum depth strata of 800–1,000 m. Active carbon transport in the CCE was 4 orders of magnitude higher than the warm core eddies. Fecal pellet production contributed to the majority (91%) of transport, and total downward carbon flux below the mixed layer was estimated at 11 mg C·m−2·d−1. When abundant, P. atlanticum swarms have the potential to play a major role in active carbon transport, comparable to fluxes for zooplankton and micronekton communities.

The high seas—marine areas beyond national jurisdiction (1)—cover nearly half of Earth's surface (2). The high seas support our planet in countless ways, from regulating the climate, to feeding millions of people, to supporting industries that contribute billions of dollars to the global economy (3). Even so, less than 1% of the high seas are fully protected (4), and the current patchwork of management and lack of oversight leaves them vulnerable to abuse. In 2017, the United Nations resolved to develop an international treaty for the conservation and sustainable use of the high seas. Negotiations are set to end this year. We must ensure that the forthcoming framework conserves high-seas biodiversity and promotes sustainable and equitable use.

Vast regions of the Central Pacific, inhabited by low-lying Micronesian nations, have been poorly studied for zooplankton. Atolls of the Republic of the Marshall Islands (RMI) have been surveyed before, during, and after the US nuclear weapons tests between 1946 and 1958, and gelatinous taxa were sporadically mentioned. Gelatinous zooplankton (GZ) were photographed during several thousand SCUBA dives between 2001 and 2016 at Kwajalein Atoll. Together with new recordings, the GZ species richness was reviewed for the entire RMI, which has the potential to become a model system for marine biodiversity research in data-poor Micronesia. Our survey resulted in 74, mostly holoplanktonic (74%), species, including nine hydrozoan medusae, 31 siphonophores, 14 scyphozoans, three cubozoans, three lobate ctenophores, eight appendicularians, one doliolid, and five salps. The species richness was low compared to census efforts from neighbouring Southeast Asian countries, hence being the first GZ assemblage characterisation for the broader oceanic region.

This study aimed to obtain the first estimates of S. thompsoni population dynamics and growth rates over the Kerguelen Plateau (Southern Indian Ocean). Micronekton, including salps, were repeatedly sampled during late summer to early autumn (26th February – 15th March 2018) at contrasting hydrological stations on the Kerguelen Plateau in the southern proximity of Kerguelen Islands. At two stations, S. thompsoni made up almost half of the micronekton biomass. Environmental conditions were important in determining the density and development of S. thompsoni populations. Growth rates (0.5–7.0% d−1) were higher than previously reported from the Antarctic Peninsula (0.3–4.6% d−1) but lower than near the Antarctic Polar Front (APF; 3.7–20.7% d−1). Despite warm surface waters (4–5 °C), low chlorophyll a concentrations restricted the salp populations from growing as fast as populations near the APF. Because the Kerguelen Plateau region deflects a branch of warm water southward towards Antarctica, more studies of S. thompsoni population dynamics across multiple seasons are needed to fully understand their importance over the Kerguelen Plateau and their invasion potential into higher latitudes.