Phytoplankton communities change in response to environmental conditions, potentially impacting zooplankton through altered trophic interactions. In the Bering Sea, warm and cold stanzas in recent decades correlated with changes in community structure of zooplankton and fish. Attempts to link these trends to primary producers based on patterns in total chlorophyll a (Chl a) concentration have been unsuccessful. Using Chl a as a proxy for food availability ignores potential consequences of community shifts in phytoplankton, which span a vast range of cell shapes, sizes, and biochemical composition that do not contribute equally to primary consumer diets. We analyzed size structure and taxonomic composition of phytoplankton in relation to environmental variables from 2003 to 2018 and examined relationships to the abundance of two copepod genera (Calanus and Pseudocalanus) important to age-0 pollock diets. Three distinct environmental stanzas were identified: Warm1 (2003-2005) with high temperature and salinity and low nutrient concentrations favoring dominance of flagellates, ciliates, and dinoflagellates, and low abundances of Calanus; Cold (2006-2012) with low temperature and salinity and high nitrogen concentrations favoring the cryptophyte Rhodomonas and small centric diatoms, and high Calanus abundances; and Warm2 (2014-2018) with high temperature, salinity, and nutrients (including high SiO4), supporting high abundances of elongated rod-like diatoms, and low abundances of Calanus. Calanus abundance (2003-2018) was significantly negatively correlated with biomass of large (> 10 mu m) phytoplankton, with moderate-strong negative correlations with the taxa Leptocylindrus, Ceratium, and Dictyocha, and strong positive correlations with Rhodomonas, highlighting links between phytoplankton and zooplankton community structure in response to alternating environmental stanzas.

Harmful algal blooms (HABs) of the toxic dinoflagellate Alexandrium catenella are increasing in the Pacific Arctic due to ocean warming. threatening ecosystems and to coastal communities that rely on marine resources for their subsistence. This study explores the potential of the Sentinel-3 remote sensing reflectance (Rrs(λ)) to detect and quantify dinoflagellate blooms in the Bering and Chukchi seas using an A. catenella cell abundance dataset to regionally parameterize and evaluate new algorithm combinations (color indexes and principal component regression - PCR). The color indexes utilize the fluorescence (FLH), green (GLH), and blue line heights (BLH) and the spectral difference in FLH peak to identify dinoflagellate blooms. The algorithms were parameterized and validated using 45 satellite match-ups with in situ A. catenella abundances measured over summer 2022 in the North Bering and Chukchi seas. Assuming the dinoflagellate bloom is dominated by A. catenella, the dinoflagellate index DINI (GLH-based) and enhanced bloom index EBI (BLH-based) provide reliable cell abundance estimates at concentrations higher than 10,000 (R2 = 0.53) and 3000 cells/L (R2 = 0.67), respectively. The PCR model resolves estimates at lower cell abundances (>1000 cells/L, R2 = 0.68). Despite their higher uncertainty, color index models provide early detection and tracking of potential A. catenella blooms, as demonstrated during Summers 2023 and 2024. By providing timely and accurate information on bloom dynamics, these satellite products can significantly augment HAB monitoring systems in the Pacific Arctic.

Pacific Arctic ecosystems are changing due to ocean warming and sea ice loss. Increases in primary production and shifts towards smaller phytoplankton and zooplankton have been recently documented, yet understanding interactions among plankton components and their responses to changing oceanographic conditions are still needed. Herein, we assess plankton responses to unprecedented warm water temperatures and low sea ice conditions during springs and summers of 2017–2019 in the Northern Bering and Chukchi seas. Record low sea ice in winter 2017–2018 was followed by high biomass of large phytoplankton (>5 μm) but low abundances of large mesozooplankton (>500 μm) species in spring of 2018, potentially due to a temporal mismatch between zooplankton and phytoplankton. The widespread distribution of warm Coastal Water in the Chukchi Sea during summer of 2019 resulted in increased biomass of small-sized phytoplankton and a mesozooplankton community characterized by small copepod species and neritic copepods. Planktonic food webs changed seasonally, with phytoplankton and mesozooplankton directly linked in spring but mediated by microzooplankton in summer. Shifts towards smaller plankton with warming will increase the number of trophic levels and reduce trophic transfer efficiencies with potential impacts on fish and shellfish resources and benthic-pelagic coupling in these ecosystems.

Several hypotheses link year-class-strength of eastern Bering Sea walleye pollock (Gadus chalcogramus) to climate variability. These focus on positive relationships with sea ice as a substrate for ice algae, as a water column stabilizer, and as a determinant of a cold pool. In 2018, sea ice was absent over the outer and middle Bering Sea shelf south of 60°N and therefore the 2018 year-class of pollock was expected to be small. However, the 2018 year-class of pollock is estimated to be the most abundant on record. We evaluated three, non-mutually exclusive hypotheses to account for the unexpected strength of the 2018 pollock year-class, 1) reduced predation on age-0 pollock, 2) reduced competition for zooplankton prey, and 3) cross-shelf transport of zooplankton in spring. We found that the northward movement of age-1 and older pollock out of the southeastern Bering Sea reduced the potential for predation on age-0 pollock over the southern shelf, as well as the potential for competition for zooplankton prey there. In contrast, the cross-shelf advection of zooplankton in spring did not appear to have influenced prey availability for age-0 pollock in late summer and fall. Thus, the northward movement of a large fraction of both age-1 as well as older pollock, not seen in the past, was at least a major contributor to the unique occurrence of an exceptionally strong year class in a warm year, 2018. As the Bering Sea warms, and if age-1+ pollock migrate northward after spawning in the southeastern Bering Sea as in 2018, it is possible that eastern Bering Sea pollock will maintain moderate to strong year-classes despite the loss of sea ice.

The Bering Sea is a highly productive subarctic ecosystem with some of the most valuable commercial fisheries in the United States. This seasonally ice-covered sea has been rapidly changing due to ocean warming with impacts to the ecosystem structure and fisheries. The long-term effects of these shifts on primary producers, however, are still unknown. Continuous monitoring of primary productivity in the Bering Sea is critical, yet observations that capture the ephemeral nature of plankton are challenging to sustain. To address this gap, high temporal resolution primary productivity rates were quantified at a mooring site (M2) in the southeastern Bering Sea in 2021. From a suite of sensors at M2 (fluorescence, dissolved oxygen, temperature, and total dissolved gas pressure), we calculated gross primary productivity (GPP), net primary productivity (NPP), and net community productivity (NCP), the latter based on net biological oxygen saturation using dissolved oxygen/nitrogen (O2/N2) ratios. These estimates elucidate weekly patterns from the spring bloom through fall, when the water column becomes well-mixed. In 2021, we observed average productivity during the spring bloom, yet wind patterns and mixing dynamics during the spring contributed to low productivity during summer and fall. The 2021 productivity metrics (GPP, NPP, and NCP) were compared across the growing season and contrasted with seasonal productivity estimates at M2 in previous years with consideration given to variability of ice conditions (warm/cold years) and wind stress.

Phytoplankton community size structure is a key attribute that influences pelagic trophic energy transfer and the vertical flux of organic matter to benthic food webs. To capture the ephemeral scale of phytoplankton population size spectra we developed an approach, combining long-term survey datasets, machine learning modeling and 3 yr of high-resolution moored vertical profiler measurements. We show that larger phytoplankton (> 10 mu m cell diameter) dominated the spring bloom throughout the water column, however, after the bloom, smaller cells (< 10 mu m cell diameter) comprise 70-80% of the phytoplankton community in the surface mixed layer. In contrast, larger cells are predominantly present at depths near the mixed layer interface. However, intermittent wind mixing events results in enhanced pulses of net community production and larger phytoplankton in the upper ocean. Our findings highlight how transient seasonal and vertical shifts in phytoplankton size structure occur in response to variable oceanographic conditions.

AbstractClimate change is altering the distribution and abundance of marine species, especially in Arctic and sub‐Arctic regions. In the eastern Bering Sea, home of the world's largest run of sockeye salmon (Oncorhynchus nerka), juvenile sockeye salmon abundance has increased and their migration path shifted north with warming, 2002–2018. The reasons for these changes are poorly understood. For these sockeye salmon, we quantify environmental and biological covariate effects within spatio‐temporal species distribution models. Spatio‐temporally, with respect to juvenile sockeye salmon densities: (1) sea surface temperature had a nonlinear effect, (2) large copepod, Calanus, a minor prey item, had no effect, (3) age‐0 pollock (Gadus chalcogrammus), a major prey item during warm years, had a positive linear effect, and (4) juvenile pink salmon (O. gorbuscha) had a positive linear effect. Temporally, annual biomass of juvenile sockeye salmon was nonlinearly related to sea temperature and positively related to age‐0 pollock and juvenile pink salmon abundance. Results indicate that sockeye salmon distributed with and increased in abundance with increases in prey, and reached a threshold for optimal temperatures in the eastern Bering Sea. Changes in population dynamics and distribution of sockeye salmon in response to environmental variability have potential implications for projecting specific future food securities and management of fisheries in Arctic waters.

The abrupt collapse of the Bering Sea snow crab stock can be explained by rapid borealization that is >98% likely to have been human induced. Strongly boreal conditions are similar to 200 times more likely now (at 1.0-1.5 degrees C of warming) than in the pre-industrial climate, while strongly Arctic conditions are now expected in only 8% of years. Stakeholders should accelerate adaptation planning for the complete loss of Arctic characteristics in traditional fishing grounds.

High-latitude ecosystems commonly experience large phytoplankton blooms in spring, which provide basal resources for a range of grazers including zooplankton, benthic consumers and fishes. Variation of the timing and intensity of the spring phytoplankton bloom influences the degree of spatial and temporal overlap with consuming organisms. In the Bering Sea, blooms occur in association with ice retreat or as pelagic open-water blooms. In the last few years, the Bering Sea shelf experienced unprecedented and widespread warming. Understanding how those climatic changes subsequently influenced phytoplankton bloom dynamics is critical for evaluating Bering Sea food web responses. We estimate spring bloom timing and type (ice-associated, open-water) across the Bering Sea shelf using a combination of data from the long-running oceanographic moorings on the eastern shelf (M2, M4, M5, M8) and satellite ocean color data from 1998 to 2022. We assess 1) if the Bering Sea shelf experienced noticeable changes in spring bloom timing or type in the last two decades, 2) whether bloom phenology was accentuated by the recent warm period (2018-2019), and 3) what influences do winds and sea surface temperatures have on spring bloom timing and where are these variables influential? Our spatial analyses reinforce the conclusion that ice retreat is the dominant forcing factor of bloom timing for the Bering Sea shelf with some influence of wind for open-water blooms. Overall, bloom timing has not shifted seasonally with climate warming in the last two decades for most of the Bering Sea shelf, except for nearshore areas and mainly in the northern Bering Sea. In warm years when ice retreats early prior to the last week of March, blooms form in open waters and bloom timing on the middle and outer shelf is delayed when wind mixing is prevalent in ice-free springs. In recent years, open-water blooms were more widespread than previously experienced, and even occurred in the northern Bering Sea during 2018-2019. A progression to more open water blooms in a future warmer climate will influence the availability of basal resources for pelagic and benthic consumers.

In the Pacific Arctic, the Chukchi Sea has been warming for decades, and exhibited an exceptionally warm period from 2015 to 2021. We examined changes in seabird distribution and abundance in the Chukchi Sea, and their relationships to environmental and prey conditions between 2 contrasting periods. We sampled systematically placed stations in late summer during 2 years before (2012, 2013) and 2 years during the warm period (2017, 2019; characterized by multiple marine heatwaves). Ship-based bird counts were used to model at-sea density of 5 seabird foraging guilds relative to oceanographic (water temperature, salinity, chlorophyll) and prey (large copepods, euphausiids, 3 forage fish taxa) variables. Relative to cool years, heatwave years were characterized by warmer, saltier waters, low abundance of large copepods and euphausiids, and elevated fish abundance, including an unprecedented abundance of age-0 walleye pollock Gadus chalcogrammus . Seabird species richness was higher during heatwave years but diversity was lower, driven by an influx of shearwaters. The best models for surface feeding and diving piscivores and diving planktivores included oceanographic and prey variables, plus a heatwave interaction term, indicating that responses to variables differed between cool and heatwave periods, with greatest disparity exhibited by diving planktivores. Models for surface planktivores were inconclusive, whereas shearwater distribution was associated with geographic variables (latitude, distance offshore), with relationships differing during cool and heatwave periods. We propose a conceptual model of how a prolonged period of marine heatwaves may affect the offshore seabird community via changes in prey species composition and distribution.

The subarctic Pacific is generally perceived as relatively homogeneous since the North Pacific Subpolar Gyre dominates the water circulation in the area. However, previous research showed significant spatial differences in phytoplankton abundance and community structure. This study aimed to identify regions associated with distinct phytoplankton phenology and composition to comprehensively describe the main phytoplankton variability patterns across the subarctic Pacific. To this end, satellite GlobColour time series observations and an extensive in situ phytoplankton pigment dataset were used in the analysis. Five bioregions were identified, based on the Self-Organized Mapping technique, using a greater than 20-year satellite data series. The bioregions in the open Pacific waters were dominated by green algae, haptophytes, and pelagophytes and were divided into the areas affected by the North Pacific Transition Zone and beyond. The other bioregions were defined around the Pacific basin margins where the diatom contribution was generally higher, with a particular distinction of waters surrounding the Kuril and the Aleutian Islands. Our bioregion designations allow for future evaluation of the processes controlling the physical and biological dynamics within each bioregion, which has direct implications for foraging conditions available to higher trophic levels, including potential food resource competition.

Arctic and subarctic ecosystems are transitioning due to ocean warming, resulting in conditions that will lead to shifts in phytoplankton communities, their nutritional compositions, and production of fatty acids (FAs). FA biomarkers are useful indicators of changing phytoplankton community composition and provide insight into basal resource quality for higher trophic level consumers such as zooplankton, fish, birds and marine mammals, yet phytoplankton FA information is largely lacking from the Bering and Chukchi Sea regions. Therefore, we analyzed suspended particulate matter (seston) FAs, chlorophyll-a (Chl-a) and environmental data collected from four surveys in the northern Bering and Chukchi Seas, two during June of 2017 and 2018 and two during August and September 2017 and 2019. Our objectives were to determine 1) whether seston FA composition was correlated with phytoplankton taxonomic composition analyzed using imaging microscope (FlowCAM) techniques, 2) if there were seasonal differences in seston FA concentrations, and 3) how FA concentrations varied with environmental variables. We found significant seasonal differences in seston FA compositions, with diatom biomarkers more prevalent in spring, followed by a community shift to dinoflagellate and small flagellate FA biomarkers in late summer. These results were confirmed by FlowCAM analyses. FA biomarkers were correlated with total and large size-fractioned Chl-a concentrations, nitrogen concentration and temperature. Lastly, we used a model framework to predict availability of the diatom-associated essential FA, eicosapentaenoic acid (EPA, 20:5n-3). Our analysis provides new information on phytoplankton FA dynamics and the important nutritional role of phytoplankton for higher trophic level consumers in the northern Bering and Chukchi Sea regions.

The Bering Sea and other high-latitude systems are experiencing unprecedented changes related to climate warming and the consequent loss of sea ice. Understanding how such changes influence primary production is a pressing question. Here, we quantify primary production rates in the southeastern Bering Sea over 4 years (2016-2019) at daily to weekly time resolution. A moored high-resolution Profiling Crawler was used in combination with in situ sampling to collect physical and biological data in the ocean's upper 50 m. We used dissolved oxygen (O-2) data to estimate gross and net primary production (NPP), and chlorophyll-a (Chl-a), temperature, and irradiance data to model NPP rates. We then assessed seasonal variation in phytoplankton production rates, phytoplankton community growth rates (p(opt)(b)) and explored to what extent summer phytoplankton community growth rates may be influenced by nitrogen limitation. Our analyses revealed that the majority of gross primary production (GPP) and net community production occurs in association with the spring phytoplankton bloom. After the bloom, the water column generally experienced low GPP and net biological carbon consumption. Phytoplankton growth rates were commonly suppressed in late summer due to apparent nitrogen depletion. Using high temporal resolution vertically resolved measurements of O-2 and Chl-a, our analyses provides important insight into how biogeochemical cycles, phytoplankton community growth rates, and carbon available for export vary seasonally in the southeastern Bering Sea.

Recent, unprecedented losses of sea ice have resulted in widespread changes in the northern Bering Sea ecosystem, and this study explores the zooplankton community response. Time-series observations were used to identify zooplankton community changes in the northern (>60°N) Bering Sea (NBS) over a 17 yr period (2002-2018). The overall objective was to determine if the changes in zooplankton populations previously described for the southeastern Bering Sea shelf (<60°N) were also observed in the NBS over alternating warm and cold periods. Particular attention was paid to more recent (2014-2018) years that showed significant losses of sea ice in the NBS (2017/2018) in comparison to a prior warm period (2003-2005) and an intervening cold period (2006-2013). A multivariate framework (redundancy analysis) was used to explore correlations with environmental conditions, and differences in mean abundance across the differing warm and cold periods were tested. The NBS zooplankton community had different responses across each warm and cold period, and the primary driver for the differences in response was sea ice. Redundancy analysis demonstrated that the zooplankton community during the second warm period experienced greater variability compared to the prior warm period. The zooplankton community had higher abundances of small copepods and meroplankton and reduced abundances of Calanus spp. and chaetognaths during the most recent warm period. This suggests that the NBS zooplankton will not be impacted by reduced sea ice when the ice coverage extends south of 60°N, but show community change once a minimum threshold in ice extent and timing of retreat is reached. Shifts in the zooplankton community may have had cascading effects on higher trophic levels that were evident during the latter warm period.

Ongoing scientific programs that monitor marine environmental and ecological systems and changes comprise an informal but collaborative, information-rich, and spatially extensive network for the Alaskan Arctic continental shelves. Such programs reflect contributions and priorities of regional, national, and international funding agencies, as well as private donors and communities. These science programs are operated by a variety of local, regional, state, and national agencies, and academic, Tribal, for-profit, and nongovernmental nonprofit entities. Efforts include research ship and autonomous vehicle surveys, year-long mooring deployments, and observations from coastal communities. Inter-program coordination allows cost-effective leveraging of field logistics and collected data into value-added information that fosters new insights unattainable by any single program operating alone. Coordination occurs at many levels, from discussions at marine mammal co-management meetings and interagency meetings to scientific symposia and data workshops. Together, the efforts represented by this collection of loosely linked long-term monitoring programs enable a biologically focused scientific foundation for understanding ecosystem responses to warming water temperatures and declining Arctic sea ice. Here, we introduce a variety of currently active monitoring efforts in the Alaskan Arctic marine realm that exemplify the above attributes.

Compression molding of carbon fiber sheet molding compounds (CF-SMC) is a promising technology to reduce the waste of carbon fiber composites and to drive sustainable development in lightweight applications. Both, the production waste of prepreg scrap and the end-of-life waste of carbon fiber components can be used efficiently in the recycling process with an apparent sandwich structure of virgin and recycled materials. This contribution investigates the technology on the example of a structural automotive component (transmission crossmember). A one-shot compression molding process was developed which enables cost-efficient, large-scale manufacturing with cycle times of about two minutes. The process–structure–property–performance relationship was experimentally characterized with manufacturing studies and prototype tests. A multilayered hybrid structure of virgin and recycled carbon fiber materials maintains the manufacturability and the mechanical performance compared to primary CF-SMC. The environmental impacts were assessed within a comparative life cycle assessment (LCA). Different material and recycling scenarios were analyzed for the components produced. It revealed lower environmental impacts than an industrially used reference version in aluminum in most impact categories. The combination of the compression molding technology with multilayered hybrid carbon fiber composites reveals opportunities for circularity and the multistage use of industrial recyclates for varying quality requirements in lightweight applications.

We investigated relationships among three metrics of sea-ice cover in eight regions of the eastern Bering Sea and the abundance of Calanus copepods, jellyfish medusae, and year-class strength of walleye pollock (Gadus chalcogrammus). In summer, Calanus spp. were more abundant over the middle shelf when sea ice lingered late into spring, and, to a lesser extent, when February sea-ice cover was heavy. Between 1982 and 1999, there were no significant (p <= 0.05) relationships between the amount or timing of sea-ice cover and pollock recruitment. However, between 2000 and 2015, pollock year-class strength was positively correlated with sea ice in the outer and middle shelves, with 17 of 24 regressions significant. Pollock year-class strength was best predicted by days with sea-ice cover after February. Pollock recruitment was positively influenced by copepod numbers, particularly in the middle shelf, with r(2) values from 0.36 to 0.47. We hypothesize that the Calanus spp. present in the southeastern Bering Sea are primarily Calanus glacialis that have been advected south in association with sea ice. None of our sea-ice metrics explained the variance in jellyfish biomass. Jellyfish biomass in our study area in the pollock age-0 year was not correlated with pollock recruitment 3 years later.

Climate change-related ocean warming and reduction in Arctic sea ice extent, duration and thickness increase the risk of toxic blooms of the dinoflagellate Alexandrium catenella in the Alaskan Arctic. This algal species produces neurotoxins that impact marine wildlife health and cause the human illness known as paralytic shellfish poisoning (PSP). This study reports Paralytic Shellfish Toxin (PST) concentrations quantified in Arctic food web samples that include phytoplankton, zooplankton, benthic clams, benthic worms, and pelagic fish collected throughout summer 2019 during anomalously warm ocean conditions. PSTs (saxitoxin equivalents, STX eq.) were detected in all trophic levels with concentrations above the seafood safety regulatory limit (80 mu g STX eq. 100 g(-1)) in benthic clams collected offshore on the continental shelf in the Beaufort, Chukchi, and Bering Seas. Most notably, toxic benthic clams (Macoma calcarea) were found north of Saint Lawrence Island where Pacific walruses (Odobenus rosmarus) are known to forage for a variety of benthic species, including Macoma. Additionally, fecal samples collected from 13 walruses harvested for subsistence purposes near Saint Lawrence Island during March to May 2019, all contained detectable levels of STX, with fecal samples from two animals (78 and 72 mu g STX eq. 100 g(-1)) near the seafood safety regulatory limit. In contrast, 64% of fecal samples from zooplankton-feeding bowhead whales (n = 9) harvested between March and September 2019 in coastal waters of the Beaufort Sea near Utqiagvik (formerly Barrow) and Kaktovik were toxin-positive, and those levels were significantly lower than in walruses (max bowhead 8.5 mu g STX eq. 100 g(-1)). This was consistent with the lower concentrations of PSTs found in regional zooplankton prey. Maximum ecologically-relevant daily toxin doses to walruses feeding on clams and bowhead whales feeding on zooplankton were estimated to be 21.5 and 0.7 mu g STX eq. kg body weight(-1) day(-1), respectively, suggesting that walruses had higher PST exposures than bowhead whales. Average and maximum STX doses in walruses were in the range reported previously to cause illness and/or death in humans and humpback whales, while bowhead whale doses were well below those levels. These findings raise concerns regarding potential increases in PST/STX exposure risks and health impacts to Arctic marine mammals as ocean warming and sea ice reduction continue.

As water flows from the North Pacific Ocean to the Arctic Ocean, it passes through the shallow eastern shelf of the Bering Sea which serves as a major sink of inorganic nitrogen. This study explores the physical and biological factors that influence the spatiotemporal variability of this sink. A regional relationship of dissolved inorganic nitrogen to inorganic phosphorus (DIN:P) was established for waters entering the shelf. Residuals from this relationship (termed N**) are a measure of the nitrogen deficit and were determined for bottom waters on the shelf using nutrient data collected on 52 hydrographic cruises spanning 2003 - 2018. Spatial variability in N** was related to advection, cross-shelf and vertical mixing, and residence time (using simulated ages of bottom water over the middle shelf). On average, this deficit accounted for approximately one-third of the inorganic nitrogen that enters the shelf, and the highest deficits (>8 mu M DIN) were observed on the middle shelf between 60 degrees N and St. Lawrence Island (63 degrees N). Temporal variability in N** was examined over the middle shelf, and higher nitrogen deficits that occurred in colder years were hypothesized to result from weaker flow and increased export of organic matter in the presence of sea ice. On the southern middle shelf, the volume integrated (40 m to bottom) seasonal change in N** was equivalent to a denitrification rate of 0.7 +/- 0.3 mmol N m(-2) d(-1). Rates of nitrogen loss were also estimated by combining N** with the simulated residence time of water on the shelf and found to be 0.20 +/- 0.02 mmol N m(-2) d(-1). These rates were comparable to prior measurements of denitrification/anammox reported on the shelf. The nitrogen deficit could not be wholly ascribed to denitrification/anammox as the N:P stoichiometric ratio in particulate matter is known to be lower at higher latitudes, and a lower ratio was observed when dissolved organic matter was measured in a small number of samples. It remains unclear how future reductions in sea ice might impact the extent of nitrogen loss in the Bering Sea.

In the eastern Bering Sea, lipid-rich copepods in the genus Calanus help to sustain productive fisheries and efficient energy flow through the ecosystem. In summer and autumn, Calanus populations consist primarily of stage C5 copepodites that are storing lipids and preparing for dormancy (diapause). We collected Calanus C5 copepodites from the eastern Bering Sea shelf in early autumn of 2015 and examined whether Calanus species composition, morphometric characteristics, and lipid-related gene expression varied along a north-south gradient. The sampled area exhibited marked differences in temperature, chl a, and Calanus abundance. However, the Calanus population was surprisingly homogeneous, composed almost entirely of C. glacialis, with no evidence for latitudinal trends in prosome size, oil sac fullness, or lipid-related gene expression. Rather than a latitudinal gradient, we found that C. glacialis from 1 southern station near the Pribilof Islands were larger and exhibited lower oil sac fullness and higher expression of lipid storage genes. Gene expression changes across stations were small relative to large shifts associated with shipboard feeding experiments. The similar characteristics of C. glacialis across stations imply that most of the C5 copepodites had experienced favorable growth conditions regardless of their latitudinal location. It remains unknown how environmental conditions affect C. glacialis physiology during other parts of their life cycle or how patterns vary among years. Continued studies of C. glacialis distribution, morphometrics, and gene expression could address these questions and serve as a harbinger for responses to future climatic changes.