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Seabirds are abundant, conspicuous members of marine ecosystems worldwide. Synthesis of distribution data compiled over time is required to address regional management issues and understand ecosystem change. Major challenges when estimating seabird densities at sea arise from variability in dispersion of the birds, sampling effort over time and space, and differences in bird detection rates associated with survey vessel type.

Using a novel approach for modeling seabirds at sea, we applied joint dynamic species distribution models (JDSDM) with a vector-autoregressive spatiotemporal framework to survey data collected over nearly five decades and archived in the North Pacific Pelagic Seabird Database. We produced monthly gridded density predictions and abundance estimates for 8 species groups (77% of all birds observed) within Cook Inlet, Alaska. JDSDMs included habitat covariates to inform density predictions in unsampled areas and accounted for changes in observed densities due to differing survey methods and decadal-scale variation in ocean conditions.

The best fit model provided a high level of explanatory power (86% of deviance explained). Abundance estimates were reasonably precise, and consistent with limited historical studies. Modeled densities identified seasonal variability in abundance with peak numbers of all species groups in July or August. Seabirds were largely absent from the study region in either fall (e.g., murrelets) or spring (e.g., puffins) months, or both periods (shearwaters).

Our results indicated that pelagic shearwaters (Ardennaspp.) and tufted puffin (Fratercula cirrhata) have declined over the past four decades and these taxa warrant further investigation into underlying mechanisms explaining these trends. JDSDMs provide a useful tool to estimate seabird distribution and seasonal trends that will facilitate risk assessments and planning in areas affected by human activities such as oil and gas development, shipping, and offshore wind and renewable energy.

 

Abundance, biomass, size and distribution of macro-jellyfish were measured in the Northern Gulf of Alaska (NGA). Nearly 1000 kg dispersed among ~13 800 jellyfish were collected using a 5-m2 Methot net. We present length-weight regressions for seven most-common taxa. Catches were dominated by the hydrozoan Aequorea victoria and the scyphozoan Chrysaora melanaster. During 2018, epipelagic macro-jellyfish biomass averaged 1.46 ± 0.36 g WW m−3 for July and 1.14 ± 0.23 g WW m−3 for September, while during 2019 they averaged 0.86 ± 0.19 g WW m−3 for July and 0.72 ± 0.21 g WW m−3 by September. Despite similar biomass among seasons within a year, July abundances were fivefold greater than abundances in September, with July catches dominated by smaller-sized jellyfish over the inner shelf, while during September larger jellyfish were more prominent and most predominant at offshore stations. Comparison to 20 years of data from standard towed nets allowed determination of the relative magnitude of the dominant carnivorous zooplankton components: scyphozoans, hydrozoans and chaetognaths in the NGA. The biomass of these smaller epipelagic predators (5.4 mg WW m−3 for hydrozoans and 10.5 mg WW m−3 for chaetognaths) is a low percentage of the macro-jellyfish, despite their much higher numerical abundance.

 

This study presents eight new high-qualityde novotranscriptomes from six co-occurring species of calanoid copepods, the first published forNeocalanus plumchrus,N. cristatus, Eucalanus bungiiandMetridia pacificaand additional ones forN. flemingeriandCalanus marshallae. They are ecologically-important members of sub-arctic North Pacific marine zooplankton communities. ‘Omics data for this diverse and numerous taxonomic group are sparse and difficult to obtain. Total RNA from single individuals was used to construct gene libraries that were sequenced on an Illumina Next-Seq platform. Quality filtered reads were assembled with Trinity software and validated using multiple criteria. The study’s primary purpose is to provide a resource for gene expression studies. The integrated database can be used for quantitative inter- and intra-species comparisons of gene expression patterns across biological processes. An example of an additional use is provided for discovering novel and evolutionarily-significant proteins within the Calanoida. A workflow was designed to find and characterize unannotated transcripts with homologies acrossde novoassemblies that have also been shown to be eco-responsive.

 

The marine coastal region makes up just 10% of the total area of the global ocean but contributes nearly 20% of its total primary production and over 80% of fisheries landings. Unicellular phytoplankton dominate primary production. Climate variability has had impacts on various marine ecosystems, but most sites are just approaching the age at which ecological responses to longer term, unidirectional climate trends might be distinguished. All five marine pelagic sites in the US Long Term Ecological Research (LTER) network are experiencing warming trends in surface air temperature. The marine physical system is responding at all sites with increasing mixed layer temperatures and decreasing depth and with declining sea ice cover at the two polar sites. Their ecological responses are more varied. Some sites show multiple population or ecosystem changes, whereas, at others, changes have not been detected, either because more time is needed or because they are not being measured.

 

Uptake of anthropogenic carbon dioxide from the atmosphere by the surface ocean is leading to global ocean acidification, but regional variations in ocean circulation and mixing can dampen or accelerate apparent acidification rates. Here we use a regional ocean model simulation for the years 1980 to 2013 and observational data to investigate how ocean fluctuations impact acidification rates in surface waters of the Gulf of Alaska. We find that large-scale atmospheric forcing influenced local winds and upwelling strength, which in turn affected ocean acidification rate. Specifically, variability in local wind stress curl depressed sea surface height in the subpolar gyre over decade-long intervals, which increased upwelling of nitrate- and dissolved inorganic carbon-rich waters and enhanced apparent ocean acidification rates. We define this sea surface height variability as the Northern Gulf of Alaska Oscillation and suggest that it can cause extreme acidification events that are detrimental to ecosystem health and fisheries.

 

How individual organisms adapt to nonoptimal conditions through physiological acclimatization is central to predicting the consequences of unusual abiotic and biotic conditions such as those produced by marine heat waves. The Northeast Pacific, including the Gulf of Alaska, experienced an extreme warming event (2014–2016, “The Blob”) that affected all trophic levels and led to large‐scale changes in the community. The marine copepodNeocalanus flemingeriis a key member of the subarctic Pacific pelagic ecosystem. During the spring phytoplankton bloom this copepod builds substantial lipid stores as it prepares for its nonfeeding adult phase. A 3‐year comparison of gene expression profiles of copepods collected in Prince William Sound in the Gulf of Alaska between 2015 and 2017 included two high‐temperature years (2015 and 2016) and one year with very low phytoplankton abundances (2016). The largest differences in gene expression were between high and low chlorophyll years, and not between warm and cool years. The observed gene expression patterns were indicative of physiological acclimatization. The predominant signal in 2016 was the down‐regulation of genes involved in glycolysis and its incoming pathways, consistent with the modulation of metabolic rates in response to prolonged low food conditions. Despite the down‐regulation of genes involved in metabolism, there was no evidence of suppression of protein synthesis based on gene expression or behavioural activity. Genes involved in muscle function were up‐regulated, and the copepods were actively swimming and responsive to stimuli at collection. However, genes involved in fatty acid metabolism were down‐regulated in 2016, suggesting reduced lipid accumulation.

 

Some of the longest and most comprehensive marine ecosystem monitoring programs were established in the Gulf of Alaska following the environmental disaster of the Exxon Valdez oil spill over 30 years ago. These monitoring programs have been successful in assessing recovery from oil spill impacts, and their continuation decades later has now provided an unparalleled assessment of ecosystem responses to another newly emerging global threat, marine heatwaves. The 2014–2016 northeast Pacific marine heatwave (PMH) in the Gulf of Alaska was the longest lasting heatwave globally over the past decade, with some cooling, but also continued warm conditions through 2019. Our analysis of 187 time series from primary production to commercial fisheries and nearshore intertidal to offshore oceanic domains demonstrate abrupt changes across trophic levels, with many responses persisting up to at least 5 years after the onset of the heatwave. Furthermore, our suite of metrics showed novel community-level groupings relative to at least a decade prior to the heatwave. Given anticipated increases in marine heatwaves under current climate projections, it remains uncertain when or if the Gulf of Alaska ecosystem will return to a pre-PMH state.

 

Organisms inhabiting high-latitude environments have evolved adaptations, such as diapause to time reproduction and growth to optimize their survival. However, the physiological regulation of the timing of complex life histories is poorly understood, particularly for marine copepods, that diapause at depth. A member of the pelagic community of the sub-Arctic Pacific Ocean,Neocalanus flemingerienters diapause in June. Egg production occurs in winter/spring. In order to characterize the transition from diapause to egg release, females were collected in late September from 400–700 m depth, incubated in the dark at 4–5 °C and sampled for RNASeq at weekly intervals. The diapause phenotype showed down-regulation of protein turnover and up-regulation of stress genes. Activation of the reproductive program was marked by the up-regulation of genes involved in germline development. Thereafter, progress through phases of oocyte development could be linked to changes in gene expression. At 5 weeks, females showed up-regulation of spermatogenesis, indicating that stored sperm had been in a quiescent stage and completed their maturation inside the female. Gene expression profiles provide a framework to stage field-collected females. The 7-week progression from diapause to late oogenesis suggests that females typically spawning in January initiated the reproductive program in November.

 

Methylmercury (MeHg) is a neurotoxin that bioaccumulates to potentially harmful concentrations in Arctic and Subarctic marine predators and those that consume them. Monitoring and modeling MeHg bioaccumulation and biogeochemical cycling in the ocean requires an understanding of the mechanisms behind net mercury (Hg) methylation. The key functional gene pair for Hg methylation,hgcAB, is widely distributed throughout ocean basins and spans multiple microbial phyla. While multiple microbially mediated anaerobic pathways for Hg methylation in the ocean are known, the majority ofhgcAhomologs have been found in oxic subsurface waters, in contrast to other ecosystems. In particular, microaerophilicNitrospina, a genera of nitrite-oxidizing bacteria containing ahgcA-like sequence, have been proposed as a potentially important Hg methylator in the upper ocean. The objective of this work was therefore to examine the potential of nitrifiers as Hg methylators and quantify total Hg and MeHg across three Arctic and Subarctic seas (the Gulf of Alaska, the Bering Sea and the Chukchi Sea) in regions whereNitrospinaare likely present. In Spring 2021, samples for Hg analysis were obtained with a trace metal clean rosette across these seas. Mercury methylation rates were quantified in concert with nitrification rates using onboard incubation experiments with additions of stable isotope-labeled Hg and NH₄⁺. A significant correlation between Hg methylation and nitrification was observed across all sites (R²= 0.34,p< 0.05), with the strongest correlation in the Chukchi Sea (R²= 0.99,p< 0.001).Nitrospina-specifichgcA-like genes were detected at all sites. This study, linking Hg methylation and nitrification in oxic seawater, furthers understanding of MeHg cycling in these high latitude waters, and the ocean in general. Furthermore, these studies inform predictions of how climate and human interactions could influence MeHg concentrations across the Arctic in the future.

 

In high-latitude environments where seasonal changes include periods of harsh conditions, many arthropods enter diapause, a period of dormancy that is hormonally regulated. Diapause is characterized by very low metabolism, resistance to environmental stress, and developmental arrest. It allows an organism to optimize the timing of reproduction by synchronizing offspring growth and development with periods of high food availability. In species that enter dormancy as pre-adults or adults, termination of diapause is marked by the resumption of physiological processes, an increase in metabolic rates and once transitioned into adulthood for females, the initiation of oogenesis. In many cases, individuals start feeding again and newly acquired resources become available to fuel egg production. However, in the subarctic capital-breeding copepod Neocalanus flemingeri, feeding is decoupled from oogenesis. Thus, optimizing reproduction limited by fixed resources such that all eggs are of high quality and fully-provisioned, requires regulation of the number of oocytes. However, it is unknown if and how this copepod limits oocyte formation. In this study, the phase in oocyte production by post-diapause females that involved DNA replication in the ovary and oviducts was examined using incubation in 5-Ethynyl-2′-deoxyuridine (EdU). Both oogonia and oocytes incorporated EdU, with the number of EdU-labeled cells peaking at 72 hours following diapause termination. Cell labeling with EdU remained high for two weeks, decreasing thereafter with no labeling detected by four weeks post diapause, and three to four weeks before spawning of the first clutch of eggs. The results suggest that oogenesis is sequential in N. flemingeri with formation of new oocytes starting within 24 hours of diapause termination and limited to the first few weeks. Lipid consumption during diapause was minimal and relatively modest initially. This early phase in the reproductive program precedes mid-oogenesis and vitellogenesis 2, when oocytes increase in size and accumulate yolk and lipid reserves. By limiting DNA replication to the initial phase, the females effectively separate oocyte production from oocyte provisioning. A sequential oogenesis is unlike the income-breeder strategy of most copepods in which oocytes at all stages of maturation are found concurrently in the reproductive structures.