KRILLPODYM: a mechanistic, spatially resolved model of Antarctic krill distribution and abundance

Robust prediction of population responses to changing environments requires the integration of factors controlling population dynamics with processes affecting distribution. This is true everywhere but especially in polar pelagic environments. Biological cycles for many polar species are synchronised to extreme seasonality, while their distributions may be influenced by both the prevailing oceanic circulation and sea-ice distribution. Antarctic krill (krill, Euphausia superba) is one such species exhibiting a complex life history that is finely tuned to the extreme seasonality of the Southern Ocean. Dependencies on the timing of optimal seasonal conditions have led to concerns over the effects of future climate on krill’s population status, particularly given the species’ important role within Southern Ocean ecosystems. Under a changing climate, established correlations between environment and species may breakdown. Developing the capacity for predicting krill responses to climate change therefore requires methods that can explicitly consider the interplay between life history, biological conditions, and transport. The Spatial Ecosystem And Population Dynamics Model (SEAPODYM) is one such framework that integrates population and general circulation modelling to simulate the spatial dynamics of key organisms. Here, we describe a modification to SEAPODYM, creating a novel model – KRILLPODYM – that generates spatially resolved estimates of krill biomass and demographics. This new model consists of three major components: (1) an age-structured population consisting of five key life stages, each with multiple age classes, which undergo age-dependent growth and mortality, (2) six key habitats that mediate the production of larvae and life stage survival, and (3) spatial dynamics driven by both the underlying circulation of ocean currents and advection of sea-ice. We present the first results of KRILLPODYM, using published deterministic functions of population processes and habitat suitability rules. Initialising from a non-informative uniform density across the Southern Ocean our model independently develops a circumpolar population distribution of krill that approximates observations. The model framework lends itself to applied experiments aimed at resolving key population parameters, life-stage specific habitat requirements, and dominant transport regimes, ultimately informing sustainable fishery management

Species distribution models describe spatial variability in mesopelagic fish abundance in the Southern Ocean

Mesopelagic fishes play a central role in the transfer of energy through open-ocean food webs, particularly in the Southern Ocean where they are both important predators of zooplankton and a key prey group for many higher predators. However, they are notoriously difficult to sample which has limited our understanding of the bio-physical predictors of their abundance and spatiotemporal variability. Species distribution models can be used to help understand species’ ecological requirements by relating records of their presence or abundance to environmental data. Here, we used data from Myctobase – a new circumpolar database of mesopelagic fishes – to model patterns in abundance of eight key myctophid species (family Myctophidae) and the genus Bathylagus in the Southern Ocean south of 45°S. We developed species-specific boosted regression tree models to obtain circumpolar predictions of abundance. Average daytime and night-time summer predictions for the period 1997 – 2011 at 0 – 200m depths were generated for each species. Depth and solar position were important predictors and species were stratified in their depth distribution. For all species except for G. nicholsi, there was an interaction between depth of capture and solar position, reflecting diel vertical migration. Other important variables included sea surface temperature, dissolved oxygen at 200 m, chlorophyll-a, and sea surface height, indicating an association with water mass properties. Circumpolar patterns of abundance varied between species with some displaying affinities for oceanic regions at Antarctic latitudes (eg. E. antarctica and Bathylagus spp.) or sub-Antarctic latitudes (eg. K. anderssoni and P. tenisoni); and affinities for shelf regions (eg.P. bolini and G. nicholsi). Our findings suggest that the abundance of mesopelagic fish is influenced by diel vertical migration and meso- and sub-mesoscale oceanographic features, with the Polar Front being a major delimiting feature. Our study showed contrasting patterns in community composition with higher species diversity north of the Polar Front that might be indicative of latitudinal variability in food web structure. Our spatial analysis is an important step toward resolving what determines important habitat for mesopelagic fishes, providing foundational information for understanding shifting food web dynamics into the future

Delivering sustained, coordinated and integrated observations of the Southern Ocean for global impact

The Southern Ocean is disproportionately important in its effect on the Earth system, impacting climatic, biogeochemical, and ecological systems, which makes recent observed changes to this system cause for global concern. The enhanced understanding and improvements in predictive skill needed for understanding and projecting future states of the Southern Ocean require sustained observations. Over the last decade, the Southern Ocean Observing System (SOOS) has established networks for enhancing regional coordination and research community groups to advance development of observing system capabilities. These networks support delivery of the SOOS 20-year vision, which is to develop a circumpolar system that ensures time series of key variables, and delivers the greatest impact from data to all key end-users. Although the Southern Ocean remains one of the least-observed ocean regions, enhanced international coordination and advances in autonomous platforms have resulted in progress toward sustained observations of this region. Since 2009, the Southern Ocean community has deployed over 5700 observational platforms south of 40°S. Large-scale, multi-year or sustained, multidisciplinary efforts have been supported and are now delivering observations of essential variables at space and time scales that enable assessment of changes being observed in Southern Ocean systems. The improved observational coverage, however, is predominantly for the open ocean, encompasses the summer, consists of primarily physical oceanographic variables, and covers surface to 2000 m. Significant gaps remain in observations of the ice-impacted ocean, the sea ice, depths >2000 m, the air-ocean-ice interface, biogeochemical and biological variables, and for seasons other than summer. Addressing these data gaps in a sustained way requires parallel advances in coordination networks, cyberinfrastructure and data management tools, observational platform and sensor technology, two-way platform interrogation and data-transmission technologies, modeling frameworks, intercalibration experiments, and development of internationally agreed sampling standards and requirements of key variables. This paper presents a community statement on the major scientific and observational progress of the last decade, and importantly, an assessment of key priorities for the coming decade, toward achieving the SOOS vision and delivering essential data to all end-users.Fil: Newman, Louise. University of Tasmania; AustraliaFil: Heil, Petra. Australian Antarctic Division; Australia. Antarctic Climate And Ecosystems Cooperative Research Centre; AustraliaFil: Trebilco, Rowan. Australian Antarctic Division; Australia. Antarctic Climate And Ecosystems Cooperative Research Centre; AustraliaFil: Katsumata, Katsuro. Japan Agency For Marine earth Science And Technology; JapónFil: Constable, Andrew J.. Antarctic Climate And Ecosystems Cooperative Research Centre; Australia. Australian Antarctic Division; AustraliaFil: Wijk, Esmee van. Commonwealth Scientific And Industrial Research Organization; Australia. Antarctic Climate And Ecosystems Cooperative Research Centre; AustraliaFil: Assmann, Karen. University Goteborg; SueciaFil: Beja, Joana. British Oceanographic Data Centre; AustraliaFil: Bricher, Phillippa. University of Tasmania; AustraliaFil: Coleman, Richard. University of Tasmania; AustraliaFil: Costa, Daniel. University of California; Estados UnidosFil: Diggs, Steve. University of California; Estados UnidosFil: Farneti, Riccardo. The Abdus Salam; Italia. The Abdus Salam. International Centre for Theoretical Physics; ItaliaFil: Fawcett, Sarah. University of Cape Town; SudáfricaFil: Gille, Sarah. University of California; Estados UnidosFil: Hendry, Katharine R.. University of Bristol; Reino UnidoFil: Henley, Sian F.. University of Edinburgh; Reino UnidoFil: Hofmann, Eileen. Old Dominion University; Estados UnidosFil: Maksym, Ted. University of California; Estados UnidosFil: Mazloff, Matthew. University of California; Estados UnidosFil: Meijers, Andrew J.. British Antartic Survey; Reino UnidoFil: Meredith, Michael. British Antartic Survey; Reino UnidoFil: Moreau, Sebastien. Norwegian Polar Institute; NoruegaFil: Ozsoy, Burcu. Istanbul Teknik Üniversitesi; TurquíaFil: Robertson, Robin. Xiamen University; ChinaFil: Schloss, Irene Ruth. Universidad Nacional de Tierra del Fuego; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Schofield, Oscar. State University of New Jersey; Estados UnidosFil: Shi, Jiuxin. Ocean University Of China; ChinaFil: Sikes, Elisabeth L.. State University of New Jersey; Estados UnidosFil: Smith, Inga J.. University of Otago; Nueva Zeland

Global Connectivity of Southern Ocean Ecosystems

Southern Ocean ecosystems are globally important. Processes in the Antarctic atmosphere, cryosphere, and the Southern Ocean directly influence global atmospheric and oceanic systems. Southern Ocean biogeochemistry has also been shown to have global importance. In contrast, ocean ecological processes are often seen as largely separate from the rest of the global system. In this paper, we consider the degree of ecological connectivity at different trophic levels, linking Southern Ocean ecosystems with the global ocean, and their importance not only for the regional ecosystem but also the wider Earth system. We also consider the human system connections, including the role of Southern Ocean ecosystems in supporting society, culture, and economy in many nations, influencing public and political views and hence policy. Rather than Southern Ocean ecosystems being defined by barriers at particular oceanic fronts, ecological changes are gradual due to cross-front exchanges involving oceanographic processes and organism movement. Millions of seabirds and hundreds of thousands of cetaceans move north out of polar waters in the austral autumn interacting in food webs across the Southern Hemisphere, and a few species cross the equator. A number of species migrate into the east and west ocean-basin boundary current and continental shelf regions of the major southern continents. Human travel in and out of the Southern Ocean region includes fisheries, tourism, and scientific vessels in all ocean sectors. These operations arise from many nations, particularly in the Northern Hemisphere, and are important in local communities as well as national economic, scientific, and political activities. As a result of the extensive connectivity, future changes in Southern Ocean ecosystems will have consequences throughout the Earth system, affecting ecosystem services with socio-economic impacts throughout the world. The high level of connectivity also means that changes and policy decisions in marine ecosystems outside the Southern Ocean have consequences for ecosystems south of the Antarctic Polar Front. Knowledge of Southern Ocean ecosystems and their global connectivity is critical for interpreting current change, projecting future change impacts, and identifying integrated strategies for conserving and managing both the Southern Ocean and the broader Earth system

Haida Gwaii kelp forest reef fish biomass spectra and trophic level data

Data supporting Trebilco R, Dulvy NK, Salomon AK & Anserson SC "The paradox of inverted biomass pyramids in kelp forest fish communities" (accepted) Proc. R. Soc. Lond. B

Island characteristics and sampling methodologies influence the use of stable isotopes as an ecosystem function assessment tool

Monitoring seabird-derived nutrients on islands following invasive mammal eradications may provide a useful, cost- and time-efficient indication of the recovery of ecosystem function; however, the technique has only been investigated on environmentally similar islands. How seabird-derived nutrients recover on islands with different characteristics, and how differences in sampling regimes affect results is poorly understood. To determine how different island characteristics (size, geographic location and invasion history) and aspects of the sampling regime (sample collection year, season and intra-island location) influence seabird-derived nutrients we collated nitrogen stable isotope (δ15N) data from three ecosystem components (soil, plants and spiders), collected on 28 islands around New Zealand. We investigated which variables best predict δ15N using linear-mixed effects models. Accounting for these variables and using still-invaded and never-invaded islands as controls for recovery, we then investigated changes in δ15N on islands at different stages following invasive mammal eradication. Island size, invasion history and the presence of seabirds in the direct vicinity of a sampling location all influenced δ15N. After accounting for these variables, δ15N increased with time since eradication in soils, plants and spiders, though there was still some variation that our chosen variables could not explain. This study demonstrates the importance of considering island characteristics and sampling methods when assessing seabird-derived nutrient recovery and highlights the need for additional targeted sample collection on islands to help separate out the effects of time since eradication and other confounding variables affecting δ15N. Improved understanding of these factors will be prerequisite for furthering this technique as a useful addition to the post-eradication monitoring tool kit.</p

Ecosystem ecology: size-based constraints on the pyramids of life. Trends in Ecology and Evolution

Biomass distribution and energy flow in ecosystems are traditionally described with trophic pyramids, and increasingly with size spectra, particularly in aquatic ecosystems. Here, we show that these methods are equivalent and interchangeable representations of the same information. Although pyramids are visually intuitive, explicitly linking them to size spectra connects pyramids to metabolic and size-based theory, and illuminates size-based constraints on pyramid shape. We show that bottom-heavy pyramids should predominate in the real world, whereas top-heavy pyramids indicate overestimation of predator abundance or energy subsidies. Making the link to ecological pyramids establishes size spectra as a central concept in ecosystem ecology, and provides a powerful framework both for understanding baseline expectations of community structure and for evaluating future scenarios under climate change and exploitation. Ecological pyramids and size spectra: size-centric views of community structure Understanding the processes that structure communities (see Glossary) in ecosystems is a fundamental goal in ecology. Elton laid the conceptual foundation for our understanding of these processes with two key observations: (i) interactions among organisms strongly shape the structure and function of communities; and (ii) the nature of these interactions is governed by both the identities and the sizes of the organisms involved These first ecological pyramids were &apos;pyramids of numbers&apos;, where the &apos;layers&apos; represented &apos;bins&apos; of body size, and the width of the layers represented the abundance of all organisms within each size class. The pyramid representation of communities quickly took hold in ecology and pyramids were re-expressed in terms of biomass [2], production, and eventually trophic level (Hutchinson, unpublished, The shape of ecological pyramids qualitatively conveys rich information about the underlying ecological processes Review Glossary Community: the biotic component of an ecosystem; organisms inhabiting a given geographic area and sharing a common resource base. Ecological pyramids: graphs of relative abundance or biomass among body-size classes or trophic levels in ecological communities 0169-5347/$ -see front matter

Distribution of larval and juvenile pelagic squids in the Kerguelen Axis region: Oceanographic influence on size structure and evidence of spawning locations

Pelagic squids are a key component in Southern Ocean ecosystems. Most species have a circumpolar distribution that is patchy in relation to major oceanographic features. However, little is known regarding where and when they spawn, or subsequently, what environmental predictors drive the size distribution particularly during early life stages. Here, we relate the size distribution of larval and juvenile squids to the oceanographic conditions around the southern Kerguelen Plateau. This is an important foraging area for many predators of squid, but there has been very little sampling effort for squids to date in that area. Seven squid species from six families were captured using depth-stratified mid-water trawls. The squids had a mantle length (ML) ranging from 7.3 to 680.1 mm, and were at their larval and juvenile form with the exception of two larger mature Galiteuthis glacialis (431.4 mm and 680.1 mm ML). Squids at stages 0 to I were predominant (ML 100 mm ML, above maturity stage I) were generally observed more in the southeast of the study domain. Squid size was positively associated with lower minimal water column temperature, higher surface chlorophyll-a concentration, and both the deepest and shallowest layers of the water column. The spatial distribution may be adaptive, helping to reduce inter- and intra-species competition and increase survivorship during early life stages. The reported relationships provide important new insights into the biophysical drivers of pelagic squid habitats around the Southern Ocean. These data significantly increase the known range of several Southern Ocean species and present implications for spawning habitat that warrant further investigation