Cancer Magister Research Articles

Do Gray Whales Count Calories? Comparing Energetic Values of Gray Whale Prey Across Two Different Feeding Grounds in the Eastern North Pacific

Predators must consume enough prey to support costly events, such as reproduction. Meeting high energetic requirements is particularly challenging for migrating baleen whales as their feeding seasons are typically restricted to a limited temporal window and marine prey are notoriously patchy. We assessed the energetic value of the six most common nearshore zooplankton species collected within the Oregon, United States range of the Pacific Coast Feeding Group (PCFG) gray whale (Eschrichtius robustus) feeding grounds, and compared these results to the energetic value of the predominant amphipod species fed on by Eastern North Pacific (ENP) gray whales in the Arctic. Energetic values of Oregon zooplankton differed significantly between species (Kruskal–Wallis χ2= 123.38, df = 5,p< 0.0001), with Dungeness crab (Cancer magister) megalopae displaying the highest mean caloric content of all tested species (4.21 ± 1.27 kJ g– 1). This value, as well as the mean energetic value of the mysidNeomysis rayii(2.42 ± 1.06 kJ g– 1), are higher than the mean caloric content ofAmpelisca macrocephala, the predominant Arctic amphipod. Extrapolations of these results to daily energetic requirements of gray whales indicate that lactating and pregnant gray whales feeding in the PCFG range would require between 0.7–1.03 and 0.22–0.33 metric tons of prey less per day if they fed on Dungeness crab megalopae orN. rayii, respectively, than a whale feeding onA. macrocephalain the Arctic. Yet, these results do not account for differences in availability of these prey species to foraging gray whales. We therefore suggest that other factors, such as prey density, energetic costs of feeding, or natal philopatry and foraging site fidelity play a role in the differences in population sizes between the PCFG and ENP gray whales. Climate change is implicated in causing reduced body condition and increased mortality of both PCFG and ENP gray whales due to decreased prey availability and abundance. Therefore, improved understanding of prey dynamics in response to environmental variability in both regions is critical.

Understanding and Advancing Natural Resource Management in the Context of Changing Ocean Conditions

Changing ocean conditions, such as ocean acidification, hypoxia, and ocean warming, are impacting marine ecosystems and posing a variety of immediate and future challenges for natural resource managers and affiliated industries. In order to successfully facilitate adaptation and mitigation responses to changing ocean conditions, research efforts and synthesis products should be developed in collaboration with resource managers and decision makers. Using interviews and surveys, we sought to advance collaborative science approaches by identifying the most pressing concerns, barriers, and research and monitoring needs of natural resource managers in Washington State, USA, where marine waters are particularly vulnerable to changing ocean conditions. Survey participants indicated that they are most concerned by ocean acidification, followed by water temperature and hypoxia. Our findings reveal a desire to prioritize laboratory and in situ studies to identify survival thresholds of ecologically or commercially important organisms, specifically zooplankton, fish, Dungeness crab, and conditions that promote harmful algal blooms. Scientific literature and in-person workshops and meetings were the preferred way for survey participants to learn about new science and affiliated results. Our findings highlight a need for continued and expanded monitoring and research efforts, the development of interpretive science products for resource managers, and enhanced communication between entities before information on changing ocean conditions can be effectively incorporated into resource management and policy decisions.

Effects of changing ocean temperatures on ecological connectivity among marine protected areas in northern British Columbia

Marine protected areas (MPAs) are important conservation tools for safeguarding marine systems, yet they are increasingly impacted by climate change. Connectivity is a fundamental aspect of MPA design and evaluation, but regional patterns of marine ecological connectivity are often not well understood, nor how connectivity patterns may be affected by climate change. Our objective was to assess how ecological connectivity between MPAs may shift with projected ocean temperature changes in the Northern Shelf Bioregion in British Columbia, Canada, and demonstrate a potential approach that can be used in other systems. We conducted a case study with Dungeness Crab (Metacarcinus magister) and Shortspine Thornyhead (Sebastolobus alascanus) using benthic temperature outputs from a regional ocean model for hindcast (1981–2010) and future (2041–2070) periods coupled with species’ environmental preference information. We evaluated MPA exposure to projected temperature changes and suitability for the adult stage of the focal species. Using existing least-cost and circuit theory-based tools more often applied in terrestrial systems, we identified potential linkages between MPAs via adult movement, simulating both optimal and probabilistic paths, then compared MPA interconnectedness between time periods. There was a marked decrease in MPA suitability and interconnectedness for Shortspine Thornyhead under projected future climates, while there was a marked increase in MPA suitability for Dungeness Crab and minor increase in MPA interconnectedness. Given the contrasting results in connectivity changes when examining just two species, this study highlights the challenge of building climate resilience in MPA network designs with multispecies objectives.

A More Comprehensive Climate Vulnerability Assessment Framework for Fisheries Social-Ecological Systems

Understanding and anticipating the effects of climate change on fisheries social-ecological systems (FSESs) is central to proactive fisheries management in a changing global climate. With fisheries management increasingly striving to consider interactions and feedbacks among people, targeted species, and the broader ecological and human communities, fisheries managers and participants need tools to help them assess these complex systems. We developed a new climate vulnerability assessment framework for analyzing the impacts of a climate-induced trend or event on a FSES. The framework divides the FSES into four interrelated and interacting domains: Ecological Community, Fished Species, Fishery, and Human Community. The framework provides a systematic approach to account for indirect as well as direct effects, links among subsystems, and multiple climate change-induced stressors. We demonstrate the framework’s utility by applying it to three case studies: the effects of a marine heatwave on the Dungeness crab FSES, the effects of a marine heatwave on the red sea urchin FSES, and the effects of long-term climate trends on North Pacific albacore. We found that the effects of a climatic trend or event on a FSES are often indirect and can trigger diverse and important feedbacks. These examples also showed that the climatic trend or event may cause changes in the temporal and spatial distribution of fishing effort and fished species that have a more significant impact on the FSES than changes to species abundance per se. Unlike other climate vulnerability assessment frameworks and applications, ours is designed to enable consideration of the range of feedbacks within and among both the ecological and human communities. As such, it is a valuable tool to guide the holistic examination and assessment of potential impacts to FSESs.

A Comparison of the Juvenile Dungeness Crab Metacarcinus magister Habitat Provided by Contemporary Oyster Aquaculture Versus Historical Native Oysters in a U.S. West Coast Estuary

Oysters and seagrasses provide structurally complex estuarine habitat for fish and invertebrate species. On the U.S. West Coast, complex oyster habitat was historically provided by the native Olympia oyster Ostrea lurida but is now provided by the commercially cultured oyster Crassostrea gigas. Ostrea lurida is found in subtidal and low intertidal areas, whereas C. gigas is predominantly cultured at higher intertidal elevations, resulting in a potential shift in available habitat for other fish and invertebrates that use this intertidal habitat. This change in the available habitat and its use was examined for the juvenile Dungeness crab Metacarcinus magister, and results showed the following: (1) comparable crab densities in remnant and restored populations of O. lurida and cultured C. gigas in two estuaries, (2) generally higher crab densities in both of these shell habitats than those observed in eelgrass Zostera marina or open mud habitat, (3) contemporary juvenile crab density in intertidal areas of Willapa Bay was most influenced by distance from the estuary mouth (declining with increasing distance) but also declined with increasing tidal elevation, and (4) when extrapolated to the estuarine ecosystem scale using areal estimates of habitat coverage, historical habitat provided by O. lurida potentially produced three times more juvenile crabs than those currently produced in cultured C. gigas. Nonetheless, both intertidal oyster habitats contribute more to juvenile crab production than eelgrass or open unstructured mud, and the ecosystem services associated with the placement of native and commercial oyster beds should be considered when defining goals for and permitting both aquaculture and native oyster restoration in Willapa Bay and other U.S. West Coast estuaries. Managers should consider this shifting temporal baseline in intertidal habitat provision, but also conducting similar evaluations at this broader estuary scale when evaluating habitat value for other resources that use these habitats differently.

The effects of population synchrony, life history, and access constraints on benefits from fishing portfolios.

Natural resources often exhibit large interannual fluctuations in productivity driven by shifting environmental conditions, and this translates to high variability in the revenue resource users earn. However, users can dampen this variability by harvesting a portfolio of resources. In the context of fisheries, this means targeting multiple populations, though the ability to actually build diverse fishing portfolios is often constrained by the costs and availability of fishing permits. These constraints are generally intended to prevent overcapitalization of the fleet and ensure populations are fished sustainably. As linked human-natural systems, both ecological and fishing dynamics influence the specific advantages and disadvantages of increasing the diversity of fishing portfolios. Specifically, a portfolio of synchronous populations with similar responses to environmental drivers should reduce revenue variability less than a portfolio of asynchronous populations with opposite responses. We built a bioeconomic model based on the Dungeness crab (Metacarcinus magister), Chinook salmon (Oncorhynchus tshawytscha), and groundfish fisheries in the California Current, and used it to explore the influence of population synchrony and permit access on income patterns. As expected, synchronous populations reduced revenue variability less than asynchronous populations, but only for portfolios including crab and salmon. Synchrony with the longer-lived groundfish population was not important because environmentally driven changes in groundfish recruitment were mediated by growth and natural mortality over the full population age structure, and overall biomass was relatively stable across years. Thus, building a portfolio of diverse life histories can buffer against the impacts of poor environmental conditions over short time scales. Increasing access to all permits generally led to increased revenue stability and decreased inequality of the fleet, but also resulted in less revenue earned by an individual from a given portfolio because more vessels shared the available biomass. This means managers are faced with a trade-off between the average revenue individuals earn and the risk those individuals accept. These results illustrate the importance of considering connections between social and ecological dynamics when evaluating management options that constrain or facilitate fishers' ability to diversify their fishing.

Footprints of fixed‐gear fisheries in relation to rising whale entanglements on the U.S. West Coast

AbstractOn the U.S. West Coast, reports of whales entangled in fishing gear increased dramatically in 2014. In this study, a time series of fishing activity maps was developed from 2009 to 2016 for the four fixed‐gear fisheries most commonly implicated in entanglements. Maps were generated using vessel monitoring system (VMS) data linked to port‐level landings databases, which were related to entangled whale reports over the same time period and with modelled distributions of humpback whales Megaptera novaeangliae Borowski. Over the full study period, neither marked increases in fishing activity nor changes in fisheries footprints within regions with high whale densities were detected. By contrast, a delayed fishery opening in California due to a harmful algal bloom in spring of 2016 led to ~5–7 times average levels of Dungeness crab Metacarcinus magister (Dana) fishing activity, which was consistent with a high rate of entanglement in that year. These results are consistent with current hypotheses that habitat compression caused by a marine heatwave increased the overlap of whales with fishing activity, despite minimal changes in the fisheries themselves. This study adds to literature on bycatch of protected species in otherwise sustainable fisheries, highlighting the value of using VMS data for reducing human–wildlife conflict in the ocean.

Benthic video landers reveal impacts of dredged sediment deposition events on mobile epifauna are acute but transitory

The “beneficial uses” of dredged sediment are increasingly being explored for habitat restoration and beach nourishment, but beneficial uses must be tempered by evaluating impacts to organisms. We studied a subtidal nearshore deposition site intended to aid beach nourishment where a “thin-layer” sediment deployment method was employed to minimize mounding and disperse sediment within a proscribed area. Baited benthic video landers (BVLs) in a Before-After Control-Impact (BACI) experimental design were used to test the acute effects (within one hour of deposition) of sediment deposition on dominant epifaunal Dungeness crab (Cancer magister) and dog whelk (Nucella spp). The effects of sediment deposition depths and the lateral surge (the turbidity front transiting the seafloor) were both considered. Observations revealed sedimentation levels were limited to <4 cm and burial likely posed no direct threat to epifauna. However, video and instrument measurements showed the lateral surge to impact the BVLs as a 1 to 3 m/s sediment-laden front. Crabs were significantly impacted, while gastropods were more resistant to dislodgment. However, the high velocity impact was relatively brief (2 to 7 min). Further, crabs returned to forage at BVLs after a mean lag of about 20 min post-impact. These results indicate an acute but ephemeral impact effect on crab, and support use of the thin-layer deposition method to minimize burial. Our novel use of BVLs in a BACI experimental design were an effective means of evaluating sediment impacts to targeted mobile epifaunal species, and video observations were informative for understanding lateral surge dynamics and the behavioral interactions of organisms.

Competency of common northern sea otter (Enhydra lutris kenyoni) prey items to harbor Streptococcus lutetiensis and S. phocae.

Streptococcus lutetiensis and S. phocae have been associated with significant morbidity and mortality in northern sea otters Enhydra lutris kenyoni in Alaska, USA, but the route and mechanism(s) of transmission remain unknown. The goal of this study was to determine the competence of common northern sea otter prey to harbor 2 species of pathogenic Streptococcus bacteria. Prey items (bay mussels Mytilus trossulus, butter clams Saxidomus giganteus, Dungeness crab Metacarcinus magister and black turban snails Tegula funebralis) were exposed to known concentrations of exponential phase cultures of S. lutetiensis and S. phocae in seawater for 24 h. A quantitative PCR assay was developed targeting the sodA gene of both S. lutetiensis and S. phocae to quantify DNA in the prey samples. Results (mean ± SD) revealed that butter clams had the highest concentration of bacteria (4.32 × 107 ± 8.20 × 106 CFU ml-1 of S. lutetiensis, 1.20 × 108 ± 2.08 × 107 CFU ml-1 of S. phocae), followed by mussels (4.26 × 107 ± 1.66 × 107 CFU ml-1, 1.16 × 108 ± 5.39 × 107 CFU ml-1), snails (1.90 × 107 ± 5.26 × 106 CFU ml-1, 5.97 × 107 ± 2.07 × 107 CFU ml-1) and crab (1.46 × 107 ± 0 CFU ml-1, 1.64 × 107 ± 0 CFU ml-1). All prey species harbored higher concentrations of S. phocae than S. lutetiensis.

Climate shock effects and mediation in fisheries

Climate shocks can reorganize the social-ecological linkages in food-producing communities, leading to a sudden loss of key products in food systems. The extent and persistence of this reorganization are difficult to observe and summarize, but are critical aspects of predicting and rapidly assessing community vulnerability to extreme events. We apply network analysis to evaluate the impact of a climate shock-an unprecedented marine heatwave-on patterns of resource use in California fishing communities, which were severely affected through closures of the Dungeness crab fishery. The climate shock significantly modified flows of users between fishery resources during the closures. These modifications were predicted by pre-shock patterns of resource use and were associated with three strategies used by fishing community member vessels to respond to the closures: temporary exit from the food system, spillover of effort from the Dungeness crab fishery into other fisheries, and spatial shifts in where crab were landed. Regional differences in resource use patterns and vessel-level responses highlighted the Dungeness crab fishery as a seasonal "gilded trap" for northern California fishing communities. We also detected disparities in climate shock response based on vessel size, with larger vessels more likely to display spatial mobility. Our study demonstrates the importance of highly connected and decentralized networks of resource use in reducing the vulnerability of human communities to climate shocks.

Climate Extreme Seeds a New Domoic Acid Hotspot on the US West Coast

A heatwave that blanketed the northeast Pacific Ocean in 2013–2015 had severe impacts on the marine ecosystem through altered species composition and survival. A direct result of this marine heatwave was a sustained, record-setting harmful algal bloom (HAB), caused by the toxigenic diatom, Pseudo-nitzschia, that led to an unprecedented delay in harvest opportunity for commercial Dungeness crab (Metacarcinus magister) and closure of other recreational, commercial and tribal shellfish harvest, including razor clams. Samples collected during a cruise in summer 2015, showed the appearance of a highly toxic “hotspot” between Cape Mendocino, CA and Cape Blanco, OR that was observed again during cruises in the summers of 2016–2018. The transport of toxic cells from this retentive site northward during wind relaxations or reversals associated with storms resulted in economically debilitating delay or closure of Dungeness crab harvest in both northern California and Oregon in 2015–2019. Analyses of historic large-scale Pseudo-nitzschia HABs have shown that these events occur during warm periods such as El Niño, positive phases of the Pacific Decadal Oscillation, or the record-setting marine heatwave. In order to reduce the impacts of large-scale HABs along the west coast of North America, early warning systems have been developed to forewarn coastal managers. These early warning systems include the Pacific Northwest and California HAB Bulletins, both of which have documented elevated domoic acid and increased risk associated with the northern California hotspot. These early warnings enable mitigative actions such as selective opening of safe harvest zones, increased harvest limits during low risk periods, and early harvest in anticipation of impending HAB events. The aims of this study are to show trends in nearshore domoic acid along the US west coast in recent years, including the recent establishment of a new seed bed of highly-toxic Pseudo-nitzschia, and to explore how early warning systems are a useful tool to mitigate the human and environmental health and economic impacts associated with harmful algal blooms.

Examining the potential conflict between sea otter recovery and Dungeness crab fisheries in California

Human exploitation of marine mammals led to precipitous declines in many wild populations within the last three centuries. Legal protections enacted throughout the 20th century have enabled the recovery of many of these species and some recoveries have resulted in conflict with humans for shared resources. With legal protections and reintroduction programs, the southern sea otter (Enhydra lutris nereis) has returned to portions of its former range from which it had been extirpated for decades, causing concern that the Dungeness crab (Cancer magister) fishery could be negatively affected by increasing otter range and population size. The Dungeness crab fishery is one of the most valuable in California, and these crabs are a known prey item of sea otters. We examine sea otter population growth by port region in relation to Dungeness crab catch using landing receipts since the early 1980s. We find Dungeness crab landings and fishing success, as measured by landings per trip receipt, increased across all ports. In the most recent decade, we observed slower growth in fishing success in northern ports where otters were absent, relative to southern ports where sea otters exist and their populations have grown. In ports where otters were present, fishing success was positively correlated with otter population size over time. Further, an extensive dataset of 83,000 sea otter foraging dives identified Dungeness crab to be less than 2% of the total diet. Though we find no evidence that sea otter populations impact the Dungeness crab fishery in California, other potential conflicts could be considered before expanding reintroduction programs.

Informing sea otter reintroduction through habitat and human interaction assessment

Sea otters Enhydra lutris have been absent from Oregon, USA, following their extirpation over a century ago. Stakeholder groups and native tribes are advocating for reintroduction to restore historic populations. We investigated the potential for successful reintroduction by: (1) estimating expected equilibrium sea otter densities as a function of habitat variables to assess sea otter habitat in Oregon; and (2) spatially relating areas of high expected densities to human activities (e.g. fisheries, recreation, vessel activity, protected areas) to anticipate potential disturbance or fishery resource competition. We estimated that 4538 (1742-8976; 95% CI) sea otters could exist in Oregon, with higher expected abundance (N = 1551) and densities (x̄ = 2.45 km-2) within the southern region. Most core habitat areas (97%), representing clusters of high expected densities, overlapped with some form of human activity. While commercial shipping and tow lanes overlapped little (1%) with core habitat areas, recreational activities (58%) and fisheries (76%) had a higher degree of overlap, posing higher disturbance risk. We anticipate higher resource competition potential with the commercial red sea urchin fishery (67% of harvest areas) than the commercial Dungeness crab fishery (9% of high-catch crabbing grounds). Our study presents the first published carrying capacity estimate for sea otters in Oregon and can provide population recovery targets, focus attention on ecological and socioeconomic considerations, and help to inform a recovery plan for a resident sea otter population. Our findings suggest current available habitat may be sufficient to support a sea otter population, but resource managers may need to further investigate and consider whether current human activities might conflict with reestablishment in Oregon, if plans for a reintroduction continue.

Characterizing the impact of recovering sea otters on commercially important crabs in California estuaries

Protective legislation and management have led to an increase in California’s sea otter Enhydra lutris nereis population. While sea otter recovery has been linked to ecosystem benefits, sea otter predation may negatively affect commercially valuable species. Understanding the potential influence of sea otters is of particular importance as their range expands into estuaries that function as nurseries for commercially valuable species like Dungeness crab Metacarcinus magister. We consider how sea otter predation has affected the abundance and size of juvenile Dungeness crab in Elkhorn Slough, California, USA, and analyzed cancrid crab abundance and size across 4 California estuaries with and without sea otters to understand how biotic and abiotic factors contribute to observed variation in crab size and abundance. We compared trends in southern sea otters relative to Dungeness crab landings in California to assess whether increasing sea otter abundance have negatively impacted landings. In Elkhorn Slough, juvenile Dungeness crab abundance and size have declined since 2012, coinciding with sea otter population growth. However, the impact of sea otters on juvenile Dungeness crab size was habitat-specific and only significant in unvegetated habitat. Across estuaries, we found that cancrid crab abundance and size were negatively associated with sea otter presence. While abiotic factors varied among estuaries, these factors explained little of the observed variation in crab abundance or size. Although we found evidence that sea otters can have localized effects on cancrid crab populations within estuaries, we found no evidence that southern sea otters, at recent population sizes, have negatively impacted Dungeness crab landings in California from 2000-2014.

Fine-scale spatial and temporal genomic variation among Dungeness crab Cancer magister larval recruits in the California Current Ecosystem

Dynamic marine environments can shape complex spatial and temporal patterns in the population connectivity of marine species, and this is often exemplified in species with long larval phases. Here, we used a genotyping-by-sequencing (GBS) approach to examine fine-scale spatial and temporal genomic variation among Dungeness crabCancer magisterlarval recruits sampled in the California Current Ecosystem. Specifically, we compared samples collected during expected- and late-season recruitment time periods within 2 consecutive years (2017 and 2018) at 2 sites in Oregon, USA (Yaquina Bay and Coos Bay). Evidence was found for high gene flow between the expected- and late-season recruits within each year and at both sites based on 1389 neutral loci. In contrast, strong genetic differentiation was observed between these 2 groups within each year and at both sites based on variation at 2 putatively adaptive loci. Contrary to prediction, the magnitude of genetic differentiation between these 2 seasonal groups was greater in 2017 when the Pacific Decadal Oscillation was stronger, upwelling was weaker, and the spring transition was later. Spatial genetic variation was not observed within 2017 or 2018. Comparing across years, expected- and late-season groups were differentiated at putatively adaptive loci. Interestingly, strong genetic differentiation was also observed between late-season groups across years. We found no evidence for cohesive larval dispersal among recruits based on genetic relatedness estimates. Overall, our findings provide evidence for high connectivity within Dungeness crab, but suggest that selective pressures and ocean conditions influence the genetic composition of larval recruits both intra- and inter-annually.

Is a delay a disaster? economic impacts of the delay of the california dungeness crab fishery due to a harmful algal bloom

During the 2015/2016 West Coast Dungeness crab (Metacarcinus magister) season, the opening of the fishery in California was delayed almost five months due to high and persistent concentrations of domoic acid in crab following a massive coast-wide Pseudo-nitzschia australis (P. australis) bloom. A hurdle model was used to estimate lost revenues to fishers due to the delay in the opening of the 2015/2016 season, and an input-output model is used to calculate resulting losses in income and employment statewide. The analysis suggests that Dungeness crab revenue was decreased as a result of the season delay, but the reduction was less than was initially estimated when a request for disaster assistance was submitted. However, the analysis also shows that fishers lost out on revenue from other fisheries equal in magnitude to the reduction in crab revenues because the delayed opening led fishers to reduce effort in non-crab fisheries. The research demonstrates the need to consider impacts beyond the revenue losses to directly affected fisheries. Potential management and industry responses that might mitigate future losses if future large scale P. australis blooms threaten fishery delays or closures are discussed along with the research needed to determine whether and how to implement these strategies.

Assessing the Relative Importance of Estuarine Nursery Habitats - a Dungeness Crab (Cancer magister) Case Study.

Estuaries serve as important nurseries for many recreationally and commercially harvested fisheries species. Recent conceptual approaches (i.e., seascape) for assessing the value of estuaries to fisheries have advocated for complex habitat-scale assessments that integrate multiple life-history responses (e.g., abundance, growth, reproduction) and ecological processes across heterogeneous landscapes. Although ecologically compelling, implementing seascape approaches may not be feasible for resource-limited management agencies. In such cases, we propose that resource managers can enhance the identification of fishery-important estuarine habitats by integrating attainable aspects of the seascape approach into a more traditional single response (e.g., abundance) model. Using Dungeness crab (Cancer magister) as a case study, we applied a spatially-explicit hybrid approach to assess the relative contribution of different estuarine habitats to that important fishery species within three Oregon estuaries (Tillamook, Yaquina, and Alsea bays). We measured the abundance of juvenile C. magister from low-tide trawls in estuarine channels and the mosaic of habitat characteristics within defined home-range distances for the crabs. After identifying and reducing strong intercorrelations among habitat variable data, we developed a best-fit model that associated crab abundance with the most influential habitat variables. We found that lower-estuary side channels supported the highest abundance of juvenile crabs; furthermore, crab abundance was positively associated with high salinity and burrowing shrimp (Upogebia pugettensis) density on adjacent unvegetated tidal flats. This hybrid method produced a habitat-specific model that better predicted juvenile C. magister abundance than did a model based on generalized habitat categories.

Chemical Exposure Due to Anthropogenic Ocean Acidification Increases Risks for Estuarine Calcifiers in the Salish Sea: Biogeochemical Model Scenarios

Ocean acidification is projected to have profound impacts on marine ecosystems and resources, especially in the estuarine habitats. Here, we describe biological risks under current exposure of anthropogenic ocean acidification in the Salish Sea, an estuarine system that already experiences inherently low OA conditions. We used the PNNL/DOE Salish Sea biogeochemical model (SSM) informed by a selection of OA-related biological thresholds of ecologically and economically important calcifiers, pteropods and Dungeness crabs. The SSM was implemented to assess current exposure and associated risk due to reduced aragonite saturation state (Ωar) and pH conditions with respect to the magnitude, duration and severity of exposure below the biological thresholds in the Salish Sea and compare it to the pre-industrial time. We further investigated individual effects of atmospheric CO2 uptake and nutrient-driven eutrophication on the changes in the chemical exposure since the pre-industrial time. Our model predicts an average decrease in Ωar of about 0.11 and average decrease in pH of about 0.06 in the top 100 m of the water column of the Salish Sea since the pre-industrial times that predispose pelagic calcifiers to increased magnitude, duration and severity of exposure. Accordingly, we demonstrate that present-day exposure is below the thresholds for pteropod sublethal effects across the entire Salish Sea basin, while mortality threshold exposure occurs on a spatially limited basis. The greatest risk for the larval Dungeness crabs is associated with the spatially limited exposures to low calcite saturation state in the South Sound in the springtime, where an increase in internal dissolution could induce additional energetic costs. The main anthropogenic driver behind the predicted impacts is atmospheric CO2 uptake, while nutrient-driven eutrophication plays only a marginal role over spatially and temporally limited scales. Reduction of CO2 emissions can help sustain biological species vital for ecosystem functions and society.

Connecting Crabs, Currents, and Coastal Communities: Examining the Impacts of Changing Ocean Conditions on the Distribution of U.S. West Coast Dungeness Crab Commercial Catch

Dungeness crab (Cancer magister) is one of the most lucrative fisheries on the U.S. west coast. There have been large spatial and temporal fluctuations in catch, which reflect the interconnected influences of the coupled natural-human fishery system. Changing ocean conditions are likely to further alter the magnitude and distribution of Dungeness crab catch, the impacts of which will propagate ecologically and through the social systems of fishing communities. Therefore, the effect of changing ocean conditions on U.S. west coast Dungeness crab catch per unit effort (CPUE) was used as an interdisciplinary case study to examine the susceptibility, a metric that integrates Dungeness crab reliance and social vulnerability indices, of coastal communities to changes in the fishery. Statistical models indicated that ocean conditions influence commercial CPUE three to five years later and that CPUE is likely to decline in the future as ocean conditions change. In particular, sea surface temperature scenarios for 2080 (+1.7 °C and +2.8 °C) reduced Dungeness crab CPUE by 30-100%, depending on fishing port latitude. Declines in Dungeness crab CPUE were greater for southern port communities than for northern port communities under both scenarios – demonstrating greater exposure at the southern end of the species range. We show that U.S. west coast communities are differentially susceptible to a decline in Dungeness crab catch, with Washington communities being at least five times more susceptible than California communities. Our overall assessment showed varying levels of risk (a combination of exposure and susceptibility) for Dungeness crab fishing ports that do not necessarily align with regional or fishery management boundaries.

Juvenile Dungeness crabs (Metacarcinus magister) selectively integrate and modify the fatty acids of their experimental diets.

Dungeness crabs (Metacarcinus magister) are ecologically and economically important in the coastal Northeast Pacific, yet relatively little is currently known about their feeding behaviour in the wild or their natural diet. Trophic biomarkers, such as fatty acids (FA), can be used to reveal trophic interactions. We used two feeding experiments to assess differences in FA composition of juvenile crabs fed different known foods to evaluate how they modify and integrate dietary FA into their own tissues and determine whether crab FA reflect diet changes over a six-week period. These experimental results were then compared with the FA signatures of wild caught juvenile crab with undetermined diets. We found that juvenile Dungeness crabs fed different foods assimilated dietary FA into their tissues and were distinct in their FA signatures when analysed with multivariate statistics. Experimentally fed juvenile crabs contained greater proportions of the most abundant long-chain polyunsaturated fatty acids (LCPUFA, >C20) than their foods. Crabs fed foods lacking in LCPUFA, particularly DHA (22:6ω3, docosahexaenoic acid), did not survive or grew slower than crabs fed other foods. This suggests that LCPUFA are physiologically important for this species and indicates biosynthesis of these FA does not occur or is not sufficient to meet their needs.This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers’: evidence and significance of consumer modification of dietary fatty acids’.