Results of analyses of genetic diversity and phylogeography for polar cod Boreogadus saida in the Pacific Arctic are presented. Analyses leverage polymorphism of Cyt b and COI gene fragments obtained from samples in the Russian Arctic, as well as samples available in open databases. According to these markers, although polar cod demonstrates high haplotype diversity, our results suggest no clear population structure within the Russian Arctic, the Beaufort Sea, and the North Atlantic. This may be explained by the peculiarities of the life cycle of polar cod, particularly oceanographic mechanisms related to the mixing of pelagic eggs and the dispersal of early juveniles by currents and their movement following ice drift within the open waters of the studied area. Results are presented within the context and consideration of existing hypotheses of the origin of the common ancestor of Boreogadus, Arctogadus and Gadus, hypotheses of the divergence of these genera, the formation of the modern range of polar cod and the causes of the genetic diversity of its mitochondrial DNA. We also provide a reconstruction of the evolution of mitochondrial lineages of polar cod, according to one of the possible scenarios of its evolutionary history.
The results of extensive research over four decades (1983-2024) investigating the spatial and depth distributions, catch per unit effort (CPUE) dynamics, and basic biological characteristics of the understudied mud skate Bathyraja taranetzi throughout its range are presented for the first time. Data used in this study were collected from Russian bottom trawl surveys and supplemented by publicly available databases. Regions with the densest aggregations of mud skate were identified in the waters along the eastern slope of the Bering Sea, off the Aleutian Islands, and in Pacific waters off southeastern Kamchatka and the northern Kuril Islands. The species was most abundant in these areas at depths between 201 and 400 m. Individual total length (TL) ranged from 11.3 to 74 cm, with the majority between 46 and 65 cm. The average TL of females was 1.8 cm larger and the average body weight was 0.17 kg greater than that of males. In the timeframe of these data, a considerable increase in the catch rate of mud skates was observed in most parts of their range. In Russian waters, CPUE initially decreased from 1985 until the early 2000s and then began to increase, while in US waters CPUE increased until 2010, after which catches began to decline.
Climate warming has impacted the Chukchi Sea resulting in reduced sea ice extent and increased water transport through the Bering Strait. This study explores the effect of recent warming by using 11 years (2010-2020) of estimated biomass data for two dominant copepods (Calanus glacialis and Pseudocalanus spp.). C. glacialis biomass declined in response to diminishing ice extent and Pseudocalanus spp. biomass increased as transport from the Bering Sea increased. Pseudocalanus spp. estimated biomass (4.61 & times; 108 kg) was four times greater than that of C. glacialis (1.13 & times; 108 kg) during the year with the lowest sea ice extent and highest transport (2019). In contrast, C. glacialis estimated biomass (1.02 & times; 109 kg) was 17 times greater than Pseudocalanus spp. (6.0 & times; 107kg) in the year with the highest sea ice extent and lowest transport (2012). The ratio of C. glacialis biomass to total biomass decreased while the same ratio for Pseudocalanus spp. increased over time. The northern Chukchi Sea had the highest C. glacialis biomass in most years; however, significant C. glacialis biomass was observed in the southern Chukchi Sea in years with greater ice extent. During warm periods, C. glacialis biomass increased in the southern Chukchi, whereas Pseudocalanus spp. were primarily located in the southern Chukchi Sea and had equal or greater biomass than C. glacialis. Shifts in biomass towards smaller, lower lipid copepod species have the potential to impact Arctic ecosystem structure and function, specifically impacting the trophic efficiency of energy transfer in the ecosystem.
The eastern Indian Ocean (IO) is a poorly characterized oligotrophic region influenced by the Indonesian Throughflow (ITF), with limited data on nutrient uptake and microbial community structure. We conducted depth-resolved measurements of nitrate and ammonium uptake, primary production and carbon-based biomasses of pico, nano and microplankton in waters overlying the Argo Abyssal Plain, downstream of the ITF. Our findings revealed picoplankton dominance of biomass, notably by Prochloroccus and heterotrophic bacteria. Primary production and phytoplankton specific growth rates declined with increasing depth (similar to 4-fold) to the deep chlorophyll maximum (DCM), suggesting that light limitation occurred at the DCM. Ammonium uptake exceeded nitrate uptake by similar to 15-fold, peaking in the upper euphotic zone, indicating strong nutrient recycling. Nitrate uptake was highest at the DCM, where phytoplankton and heterotrophic bacteria biomass increased. Nighttime nitrate uptake and a low median f-ratio (similar to 0.05) emphasizes the importance of nutrient recycling in this region. Our study enhances our understanding of nitrogen cycling, microbial community structure, and productivity in the Argo Basin, offering a valuable baseline for assessing future changes in oligotrophic ocean productivity.
In the Humboldt Current System, recurrent episodes of ocean warming drive large shifts in the abundance and accessibility of small pelagic prey, with widespread consequences for seabird populations. For Humboldt penguins (Spheniscus humboldti, HUPE), this threat is magnified given the recent reduction of one of its historically most important colonies, Punta San Juan (PSJ). We evaluated the influence of local warming events on the HUPE adult population at PSJ from 2012 to 2024 at two temporal resolutions, monthly and interannually. We estimated monthly average sea surface temperature (SST) values from 2012 to 2024 within the HUPE foraging range off PSJ as a proxy of local fluctuations in environmental conditions (source: MODIS). We then used GLMs at a monthly resolution to estimate SST association with two HUPE population parameters: adult population and reproductive success (ratio of chicks/adults). Reproductive success declined during the warm period of 2015, increased following the onset of cooler conditions in 2018, peaked in 2021-2022 during a particularly cold phase, and declined again in 2023-2024 as temperatures rose. Therefore, our study shows that the reproductive success of HUPE had an immediate response to SST trends (negative association) explaining the decrease in breeding failure with increased SST. In contrast, the adult population continuously decreased from 2016 until 2024 despite colder conditions between 2018 and 2022. Results highlight the complexity of HUPE response to SST anomalies as well as contrasting results when evaluated at monthly or interannual resolutions. We found differences between short-term reproductive responses (i.e. breeding failure) and long term demographic responses (i.e. adult dispersal or mortality). We recommend future studies to elucidate how rapidly changing climate scenarios can affect trophic food webs and other HUPE demographics, such as survival, in synergy with other potential threats (e.g. fishery pressure) at different temporal and spatial scales.
Our knowledge of the deep-sea fauna around Christmas Island and Cocos (Keeling) Islands in the central-eastern Indian Ocean was very limited. In 2021 and 2022, two voyages of discovery on the RV Investigator sampled benthic deep-sea habitats in the region. Sixty-seven benthic macrofaunal samples were obtained from 22 seamounts, the two island groups and the surrounding abyssal plain, ranging in depth from 94 to 5431 m. The collected material was identified to 1059 taxonomic units by taxonomists. Of these, only 495 (47%) were identified to a described species, another 149 (14%) were new species, and the remainder required additional taxonomic work to determine whether they were new or previously described. Decapods and fishes provided the most species, but ophiuroids were the most abundant taxa overall. Faunal community analyses were predominantly structured by depth, with geographic location being important within depth bands. There was a continual turnover of species from shallow to abyssal depths, particularly in the upper 1500 m of water. Seafloor habitats shallower than 1000 mare rare in the eastern Indian Ocean and form important conservation assets.
We deployed a Trawl-Resistant bottom-mounted mooring (TRBM) in Awang Bay, Indonesia, and successfully obtained months of high-frequency data (7-month temperature-depth and 4-month velocity data) to study multiscale oceanic variability in the southern Maritime Continent (SMC). A prominent quasibiweekly oscillations (QBWOs; 10-20-day period) in ocean current velocity and bottom water temperature were identified. This signal indicated significant bottom disturbances, with temperature amplitudes reaching 3 degrees C and meridional velocity anomalies of 0.1 m/s. Reanalysis data revealed that this QBWO propagates eastward along the SMC as coastal Kelvin waves, with a phase speed of 1.44-2.89 m/s. This kind of biweekly Kelvin wave is driven mainly by biweekly wind anomalies in the SMC instead of propagating remotely from the equatorial Indian Ocean. This study reveals the existence and mechanism of QBWOs along the coast of SMC, which have significant implications for marine ranching and coral systems.
The southeastern coast of Vietnam (SCV) hosts one of the most productive upwelling systems in the South China Sea (SCS) during summer. Previous studies have shown that large-scale climate mode such as the El Nino-Southern Oscillation (ENSO) can influence Chlorophyll-a (Chla) variability in this region. However, this influence alone cannot account for the overall interannual variability of Chla, implying the involvement of additional atmospheric processes. Using over two decades of satellite observations and reanalysis data, we identified a much closer relationship between summer Chla variability in the SCV and the Western Pacific Subtropical High (WPSH) index compared with that with ENSO index. The westward extension of the WPSH over the SCS suppressed southwesterly wind anomalies, thereby weakening wind-driven Ekman transport and coastal upwelling. The weakened upwelling reduced nutrient supply to surface waters, restraining phytoplankton growth and leading to lower summer Chla concentrations in the SCV. Furthermore, based on CMIP6 projections, the intensity of the WPSH exhibits an opposite trend to summer Chla variability in the SCV, with a negative correlation persisting under future climate scenarios. These results not only identify the WPSH as a more direct atmospheric forcing driving Chla variability in the SCV during summer, but also suggest that its intensity possesses strong predictive potential for interannual Chla changes.
Mesoscale eddies are fundamental to the ocean's energy and tracer transport, yet their vertical structures remain poorly quantified despite their key role in linking surface and deep-ocean processes. Previous studies have revealed diverse eddy types, from surface-intensified to subsurface and deep-layer eddies, but lacked a unified framework for describing their three-dimensional structures. Moreover, the relative abundance and spatial distribution of different vertical eddy types in the global ocean remain poorly understood. Here, we develop an idealized diagnostic framework that characterizes eddy vertical structures using two physically interpretable parameters: the core depth and the e-folding vertical scale of the rotational velocity profile. Applying this method to an eddy-resolving ocean reanalysis in the Kuroshio Extension, we classify mesoscale eddies into five types: surface-intensified eddies (SE), abnormal interior-intensified eddies (AIE), normal interior-intensified eddies (NIE), deep interior-intensified eddies (DIE), and full-depth interior-intensified eddies (FIE). Interior-intensified eddies account for nearly half of the total and extend to depths beyond 3000 m. The same framework is further applied to the South China Sea, one of the largest semi-enclosed deep marginal seas of the world's oceans, where the five types of mesoscale eddies are all found, but the first 3 types account for similar to 99.8%. Notably, the interior-intensified types AIE and NIE contribute similar to 60% in the SCS, indicating a pronounced prevalence of subsurface eddies with characteristic scales that differ from those in the KE region. Furthermore, in both regions, the vertical structures of the fastest-growing baroclinic instability modes show striking correspondence with the classified eddy types, suggesting that baroclinic instability provides a common dynamical basis for the formation and vertical structuring of mesoscale eddies in both open-ocean and marginal-sea environments.
As the important hotspots of biodiversity, seamounts have an impact on the surrounding marine ecosystems because of their distinct topographic features and environmental parameters. To clarify the influence mechanism of the "seamount effect" of three different types of seamounts, the characteristics of zooplankton communities (i. e., the abundance, diversity, dominant species, and biomass) at the Caroline, Yap, and Kocebu seamounts in the western Pacific Ocean (WPO) were studied. We collected and identified the 310, 197, and 151 zooplankton species/taxa at the Caroline, Yap, and Kocebu seamount areas, respectively. The dominant species/taxa of zooplankton community at the Caroline, Yap, and Kocebu seamount areas were 11, 10, and 8, respectively. The highest values for the biodiversity index (3.71) and abundance (28.85 ind/m3) appeared at the Yap seamount and Caroline seamount, respectively. The high zooplankton diversity was not consistent with the high zooplankton abundance at the three seamounts. The zooplankton dry weight biomass (DW) at the Caroline and Kocebu seamounts was dominated by zooplankton more than 2000 mu m in size. However, the proportion of different sizes in zooplankton DW was relatively uniform at the Yap seamount area. ZooScan results showed that the zooplankton carbon biomass (CB) at the three seamount areas was dominated by copepods (>50%). We observed significant differences between the zooplankton groups/taxa with the second and third most dominant CB proportions (Kruskal-Wallis tests, p < 0.01). Larvae accounted for a relatively high proportion of CB at the Caroline seamount, whereas the proportions of Euphausiid and Chaetognaths at the Yap and Kocebu seamounts were different. Zooplankton gaps were found at all three seamounts. The horizontal distribution patterns of abundance and biomass of the zooplankton community differed among the three seamounts. Correlation analysis showed that the zooplankton abundances at the Caroline and Yap seamount were significantly positively correlated with chlorophyll concentration, whereas the zooplankton abundance and biomass were negatively correlated with seawater temperature at the Kocebu seamount. Combined with the results of the principal components analysis and BIO-ENV, the primary environmental factor affecting the distribution of the zooplankton community at the Kocebu and Caroline seamount was seawater temperature and salinity, respectively. However, the horizontal distribution of the zooplankton community at the Yap seamount was simultaneously affected by multiple environmental factors. We found that the Yap and Kocebu seamount exhibited "seamount effects" on zooplankton communities, but we did not observe any obvious "seamount effect" on zooplankton community at the Caroline seamount area. These findings suggest that the shallow seamounts were not necessarily associated with stronger zooplankton community responses than the intermediate or deep seamounts in the WPO. These results provide valuable insight into the ecological responses of zooplankton community to different types of seamounts, thereby contributing to understanding the mechanism of the "seamount effect".
The jack mackerel (Trachurus murphyi) fishery in the Southeast Pacific Ocean is strongly influenced by environmental conditions, particularly sea surface temperature (SST). This study aims to improve the predictive performance of fishery models by incorporating environmental variability into surplus production models and by applying advanced deep learning techniques. We developed and validated multivariate autoregressive models based on Convolutional Neural Networks (CNNs) and Long Short-Term Memory (LSTM) networks to simulate jack mackerel catches under contrasting environmental scenarios. Sea surface temperature and fishing effort were used as the main explanatory variables, with lag structures included to capture delayed relationships between environmental conditions and fishery yields. The results show that both the CLIMPROD model and the deep learning architectures provide robust predictive performance. The selected CLIMPROD model achieved an R2 of 0.87, while the best CNN and LSTM models attained R2 values of 0.94 and 0.85, respectively. These approaches improve upon more classical formulations by accounting for the nonlinear effects of environmental variability on fishery dynamics. Simulations under different SST scenarios indicate that warmer periods tend to produce higher jack mackerel catches than colder periods, highlighting the influence of SST on fishery productivity. Overall, the findings support the value of incorporating environmental variability into fishery models to improve the accuracy and reliability of management-oriented analyses.
Southern bluefin tuna (SBT), Thunnus maccoyii, is a long-lived, migratory pelagic species that spawns exclusively south of the Java Sea, off the northwestern coast of Australia. Among the bluefin tunas, the larval ecology of SBT remains the least studied, despite major technological advances in early life history dynamics to inform management strategies for larval and juvenile stages. During the peak spawning season in the austral summer of 2022, plankton tows were conducted in this region for the first time in 35 years, targeting SBT and other co-occurring scombrids from surface waters (similar to 30 m depth). This study reassessed the presence, spatial distribution, and relative abundance of larval scombrids as part of the BLOOFINZ (Bluefin Larvae in Oligotrophic Ocean Foodwebs, Investigations of Nutrients to Zooplankton - Indian Ocean) cruise. Herein we describe collection methods, abundance, and diel patterns of larval scombrids in the study area whose growth, diet, and trophic ecology are examined in companion studies in the BLOOFINZ-INDITUN special issue of this journal. Larval identifications were conducted using taxonomic keys, with 11% confirmed by multiple genetic tools (multiplex PCR, COI sequencing, and high resolution melting). SBT dominated the larval scombrid assemblage and most frequently co-occurred with Thunnus alalunga and Thunnus albacares. SBT abundance averaged 35.8 +/- 47.7 (mean +/- Standard Deviation, with median 14.25) individuals per 1000 m(-3), with a peak occurring approximately one week after the full moon. A high-density patch of fish eggs (>82,000 1000(-1) m(-3)) was also recorded. Developing robust, spatiotemporally relevant abundance estimates is critical for continued effective management of tuna fisheries.
Copepods of the genus Calanus are central to the ecological and biogeochemical functioning of polar pelagic ecosystems. They graze on seasonal phytoplankton blooms, collectively releasing large quantities of fast-sinking faecal pellets as they convert ingested food into carbon-rich lipid reserves. Towards the end of summer, they migrate down to bathyal and abyssal depths and overwinter by subsisting on their lipid reserves until the following spring. This ontogenetic vertical migration, the so-called 'seasonal lipid pump' (SLP), actively transports enormous quantities of organic matter and surface-derived carbon into the deep ocean. Quantification of the SLP's contribution to the global carbon cycle has attracted major interest, yet little is known about trophic connections between Calanus spp. and deep-sea benthic ecosystems. We address this knowledge gap by undertaking lipid biomarker analysis and determining delta 15N signatures of Calanus spp. and selected benthic taxa collected from 1255 to 5414 m in the Fram Strait, Arctic Ocean. Calanus spp. lipid profiles were dominated by C20:1 and C22:1 fatty acids and alcohols. Substantial quantities of these biomarkers were present in the lipids of all the benthic taxa examined: mean relative abundances ranged from 11.18 mol% in holothurians (trophic level = 1.73) to 29.27 mol% in mysids (trophic level = 2.85). These results suggest an important trophic connection between Calanus spp. and deep-sea benthic Arctic ecosystems. We discuss the likely routes through which individual taxa obtain these biomarkers and highlight the potential significance of this trophic link as a pathway for the transferral of organic matter into the deep-sea.
Fram Strait is the main gateway between the Arctic Ocean and the North Atlantic, where warm, saline Atlantic Water (AW) flows northward via the West Spitsbergen Current (WSC) - the main source of oceanic heat and salt entering the Arctic Ocean. An array of moorings has continuously monitored the year-round inflow of AW in the WSC from 1997 to 2024, providing a 27-year record of hydrographic and current measurements. A robust, long-term AW warming trend of 0.20 degrees C per decade was identified, amounting to a total increase of 0.54 degrees C over the observational period. Distinct multi-annual warm and cold anomalies were identified, typically lasting similar to 2 years. Two warm periods (2005-2007 and 2015-2017) and two cold periods (1997-1999 and 2019-2024) are linked to distinct shifts in the AW temperature regime. These anomalies were generally accompanied by salinity changes, with warm periods associated with more saline conditions and cold periods with fresher waters. The most recent cold anomaly is notable for persisting for over five years - more than twice as long as previous events. Interannual variability in AW temperatures reflects a combination of upstream advection of anomalies from the Nordic Seas and modulation by local atmospheric forcing. These temperature anomalies are advected into the Eurasian Basin and influence downstream conditions. The expected continued AW warming and associated increase in ocean heat transport will have profound and lasting implications for the physical and ecological future state of the Arctic Ocean.
This study investigates spatial and temporal patterns in zooplankton abundance and community composition in the Fram Strait between 2011 and 2023. The region is shaped by contrasting hydrographic regimes: warm, saline Atlantic Water transported northward by the West Spitsbergen Current (WSC) in the east, and cold, fresh Polar Water carried southward by the East Greenland Current (EGC) in the west. While the WSC has been extensively studied, the EGC remains less well understood. Yet, monitoring both regimes is essential to detect changes related to ongoing Atlantification. As part of the LTER observatory HAUSGARTEN, zooplankton were sampled at nine sites across Fram Strait using vertical multinet hauls (150 mu m mesh, 1500-1000-500-200-50-0 m depth). Preserved samples were scanned and analysed using the web-based platform EcoTaxa. In total 86 taxa were identified, with Copepoda, particularly Oithona and Calanus spp., dominating the communities. Abundances in the EGC were relatively stable and consistently lower than in the WSC. In the WSC, zooplankton abundances varied considerably and occasionally reached extremely high values that might be linked to mesoscale hydrographic features. We applied Generalized Additive Models to our data, that revealed significantly declining abundances over time in the WSC while they increased in the EGC. Shannon diversity and Pielou's evenness, however, had increased slightly in both regions in the last three years. Climate change is likely to affect the two regimes differently, leading to diverging ecosystem responses. Thus, our findings underscore the importance of sustained long-term monitoring to fully understand zooplankton dynamics in the entire Fram Strait.
The Sulu Sea is a semi-enclosed marginal sea in the Maritime Continent with a maximum depth of -5000 m and communicates with adjacent seas through shallow straits. Recent studies have detected enhanced warming trends in its subsurface and deep layers since the 1990s. Based on observational datasets, we show that the 0-500 m ocean heat content (OHC) of the Sulu Sea exhibits prominent interannual variability superimposed upon a significant warming trend. Analysis of the 1/12 degrees GLORYS12V1 data (Global Ocean Reanalysis and Simulation version-12v1) reveals that these interannual variations are predominantly caused by the El Nino-Southern Oscillation (ENSO) through coastally trapped baroclinic oceanic waves. Specifically, during La Nina events, the clockwise propagation of downwelling waves around the Philippines causes a larger decline in the Sibutu Passage outflow than in the Mindoro Strait inflow, leading to a convergence of upper-layer warm waters in the Sulu Sea. The long-term warming trend is primarily attributable to warming of inflow waters, rather than local heating by surface fluxes. Further analysis reveals that compared to other regions of the Indo-Pacific warm pool, the heat accumulation in the Sulu Sea extends to larger depths and causes stronger warming rates in the deep Sulu Sea. The weak stratification in the Sulu Sea, regulated by its exceptionally warm deep-layer temperatures in climatology, facilitates the downward penetration of anomalous heat through diapycnal mixing. These findings provide a candidate explanation for the deep-layer heat storage "hotspot" in this unique marginal sea, with implications for regional biogeochemical cycles and marine ecosystems.
A novel Subsea Winched Profiling System (SWIPS) was deployed in the Atlantic Water (AW) inflow to the Arctic Ocean north of Svalbard, providing high-resolution, year-round observations of upper ocean hydrography and biogeochemistry. Between July 2022 and July 2023, SWIPS collected 85 vertical profiles from similar to 125 m to 10 m depth at 4-day intervals, capturing seasonal transitions and fine-scale variability across open water and ice-covered conditions. The autonomous system provides a sustained Eulerian perspective of upper ocean dynamics, resolving the evolving water mass distribution, seasonal stratification, the deepening of the mixed layer in autumn and winter, and the persistent influence of AW beneath a strongly stratified surface layer. SWIPS captured an under-ice phytoplankton bloom in May 2023, occurring under > 80% sea ice concentrations and preceding the onset of Polar Day by more than one week. During peak bloom periods, satellite-derived chlorophyll concentrations underestimated in-situ values by up to an order of magnitude due to persistent subsurface chlorophyll maxima and ice cover. The profiler also detected two episodes of anomalous winter hydrography during which AW reached the surface and disrupted the expected cold, stratified regime. The hydrographic data and satellite sea surface temperature suggest these events were driven by upstream AW advection from Fram Strait and facilitated localized convection to depths exceeding 100 m, reinforcing the role of remote forcing in shaping local upper ocean and ice conditions. By capturing both gradual seasonal evolution and short-lived anomalies, SWIPS provides critical in-situ observations that complement traditional observational methods and improve understanding of ocean-ice-ecosystem interactions under Arctic amplification.
The HAUSGARTEN observatory consists of 21 stations at which, since 1999, abiotic and biotic processes in Fram Strait are being monitored. As the Transpolar Drift continuously transports sea ice from the central Arctic Ocean toward Fram Strait, some stations are covered seasonally or even year-round by closed ice pack. Previous studies have shown that when sea ice is present, it can exert direct or indirect effects on the underlying water column, extending all the way down to the seafloor. In this manuscript, we provide an overview and a more thorough assessment of the sea-ice conditions at the N3-5 and EGI-IV stations, focusing on both seasonal variability and long-term changes in satellite data. The western stations (EGI-IV) show significantly higher ice coverage, whereas the northeastern stations (N3-5) persistently exhibit lower ice concentrations. Somewhat unexpectedly, and in contrast to the rest of the Arctic, sea-ice concentration at these stations shows no significant trends-neither on an annual nor on a monthly timescale. Although no direct changes in ice coverage are apparent, noticeable changes in ice properties do occur. The age of the ice at both locations has declined sharply. Its origin has shifted northward, thereby reducing the proportion of ice formed in shallow-water regions and interrupting the transport of ice-rafted matter from the Siberian shelves towards Fram Strait.
During the initial 25 years of operation, the Long Term Ecological Research (LTER) observatory HAUSGARTEN has facilitated the generation and collection of a huge array of data and data types from the Fram Strait, Arctic. These data have supported 200+ primarily environmental, biological and climate studies related publications, as well as provided input data for climate prediction models and a host of other large data investigations in topics ranging from surface/seawater gas exchange to deep sea meiofauna abundances in the vicinity of food falls.These data are hugely valuable for future trans disciplinary studies on ecosystem functioning and response to environmental change, as well as providing input to other future studies, such as temporal faunal abundance or distribution studies. To better support future research endeavours there has been a progressive drive across the environmental research community to permanently archive and make environmental research data freely available to researchers, the public and legislators environmental research data globally. The site of the LTER observatory HAUSGARTEN, at the Arctic - Atlantic intersection renders it a site of particular interest during the ongoing global environmental changes.In this paper we introduce the open access long term storage archives which are the repositories for much of the LTER observatory HAUSGARTEN monitoring and experimental results, and introduce some of the new and novel ways such archived data can now be accessed readily by individuals not directly involved in data collection.
The microbial food web in the spawning region for Southern Bluefin Tuna (SBT) off northwest Australia exhibits Prochlorococcus dominance, high protistan grazing, and significant mixotroph functionality. We investigated these qualities expressed in the trophic structure of the zooplankton community through two approaches: bulk stable isotope analysis (SIA) and compound-specific isotope analysis of amino acids (CSIA-AA). Trophic positions (TP) were compared for five size fractions (0.1-5 mm) and for seven taxonomic groups (appendicularians, Oncaea spp., calanoid copepods <1 mm, Corycaeus spp., Lucifer spp., calanoid copepods >1.8 mm, and chaetognaths) representing potential prey and carnivorous competitors of SBT larvae. Size-fractioned SIA gave unrealistic TP ranges and large site variability. SIA of taxonomic groups and CSIA-AA results showed similar TP patterns and low site variability. The role of protistan consumers, determined from delta N-15 enrichment differences between trophic AAs alanine and glutamic acid, increased with zooplankton size from 0 to >1.0 trophic steps. Appendicularians had low TP, indicating direct feeding on primary producers. A similar TP for Oncaea spp., as well as lower delta N-15 enrichment of carnivorous taxa, suggested that discarded appendicularian houses with filter-concentrated phytoplankton were used as a dietary supplement within the assemblage. Overall results indicated a compressed and efficient food web of a maximum of two trophic steps where appendicularians linked picophytoplankton-dominated productivity to tuna larvae, and where intermediate trophic steps for protistan grazers applied mainly to >0.5-mm zooplankton. A clear isotopic signature of protistan mixotrophy was absent, suggesting a missing excretory enrichment step as an hypothesis for future study.
