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Map of the Dungeness crab sampling sites off the coast of British Columbia and Oregon. Site names correspond to the sites listed in Table 1.
Source publication
Limited approaches exist for studying population connectivity in widely dispersing marine benthic invertebrates. Genetic techniques can provide important insights toward identifying recruitment trajectories. Here, 10 microsatellite loci were used to examine connectivity among Oregon Dungeness crabs (Cancer magister, Dana, 1852) in the California Cu...
Contexts in source publication
Context 1
... collaboration with the Oregon Department of Fish and Wildlife and the commercial crab fishing fleet, Dungeness crabs (Cancer magister) were sampled off the Oregon coast during the 2011 Preseason test fishery (Pacific States Marine Fisheries Com- mission 2014). The sampling design consisted of 12 latitudinal transects with six crab pots fished at three different depths (27, 55, and 82 m) (Fig. 1). Each transect line represents a sampling site for a total of 12 sampling sites in Oregon. Muscle tissue from the hind leg of each female and sublegal size male (<158 mm carapace width) crab was collected and stored in a 50-mL vial filled with 95% ethanol (n ¼ 801; Table 1). All legal size male crabs from the test fishery were transported to seafood processors for meat recovery and were not available for genetic analysis. In addition, DNA samples from two sites (Alison Sound n ¼ 54 and Boundary Bay n ¼ 48; Fig. 1 Beacham et al. 2008) were included in the ...
Context 2
... collaboration with the Oregon Department of Fish and Wildlife and the commercial crab fishing fleet, Dungeness crabs (Cancer magister) were sampled off the Oregon coast during the 2011 Preseason test fishery (Pacific States Marine Fisheries Com- mission 2014). The sampling design consisted of 12 latitudinal transects with six crab pots fished at three different depths (27, 55, and 82 m) (Fig. 1). Each transect line represents a sampling site for a total of 12 sampling sites in Oregon. Muscle tissue from the hind leg of each female and sublegal size male (<158 mm carapace width) crab was collected and stored in a 50-mL vial filled with 95% ethanol (n ¼ 801; Table 1). All legal size male crabs from the test fishery were transported to seafood processors for meat recovery and were not available for genetic analysis. In addition, DNA samples from two sites (Alison Sound n ¼ 54 and Boundary Bay n ¼ 48; Fig. 1 Beacham et al. 2008) were included in the ...
Citations
... This implies prolonged exposure to less suitable habitats characterized by low ΔΩ cal,60 in the nearshore areas that can exacerbate negative biological effects but some of them could be counteracted by higher food availability. With respect to genetic connectivity, the status of Dungeness crab as a high gene-flow species with low genetic differentiation along the US West Coast and the lack of significant adaptation patterns Jackson et al., 2018;O'Malley et al., 2017) implies that the genetic pool that might allow for adaptation under future climate scenario will be limited. This points toward the need for more comprehensive population vulnerability assessment that can link OA vulnerability with the population genetics. ...
Ocean acidification (OA) along the US West Coast is intensifying faster than observed in the global ocean. This is particularly true in nearshore regions (<200 m) that experience a lower buffering capacity while at the same time providing important habitats for ecologically and economically significant species. While the literature on the effects of OA from laboratory experiments is voluminous, there is little understanding of present-day OA in-situ effects on marine life. Dungeness crab (Metacarcinus magister) is perennially one of the most valuable commercial and recreational fisheries. We focused on establishing OA-related vulnerability of larval crustacean based on mineralogical and elemental carapace to external and internal carapace dissolution by using a combination of different methods ranging from scanning electron microscopy, energy dispersive X-ray spectroscopy, elemental mapping and X-ray diffraction. By integrating carapace features with the chemical observations and biogeochemical model hindcast, we identify the occurrence of external carapace dissolution related to the steepest Ω calcite gradients (∆Ωcal,60) in the water column. Dissolution features are observed across the carapace, pereopods (legs), and around the calcified areas surrounding neuritic canals of mechanoreceptors. The carapace dissolution is the most extensive in the coastal habitats under prolonged (1-month) long exposure, as demonstrated by the use of the model hindcast. Such dissolution has a potential to destabilize mechanoreceptors with important sensory and behavioral functions, a pathway of sensitivity to OA. Carapace dissolution is negatively related to crab larval width, demonstrating a basis for energetic trade-offs. Using a retrospective prediction from a regression models, we estimate an 8.3% increase in external carapace dissolution over the last two decades and identified a set of affected OA-related sublethal pathways to inform future risk assessment studies of Dungeness crabs.
... Previous genetics studies analyzing 10 neutral microsatellite loci have found evidence for genetic differentiation among the Dungeness crab from different ecosystems along the west coast of North America. For example, O'Malley et al. (2017) found evidence for strong genetic differentiation (F ST > 0.16) between benthic stage Dungeness crab in coastal Oregon (CCE) and in British Columbia (samples from both the southern GOA and the northern SSE). A second study utilizing the same methods, but different geographic sampling locations, found evidence for weak, yet significant genetic differentiation (F ST range = 0.002-0.004) ...
... (2) provide evidence for genetic differentiation between benthicstage Dungeness crab from the CCE and northern ecosystems O'Malley et al., 2017). Furthermore, we identified two putatively adaptive loci, for which strong genetic differentiation was observed between expected-season and late-season recruits. ...
... The GBS approach used in this study allowed for the identification of over a thousand loci including two putatively adaptive loci, where past genetic studies on Dungeness crab used 10 neutral microsatellite loci O'Malley et al., 2017). Using both neutral and adaptive loci together to examine genomic variation within a species is advantageous because it provides information on gene flow and genetic drift, as well as natural selection. ...
The California Current Ecosystem (CCE) is a dynamic marine ecosystem from which many socioeconomically important fisheries species are harvested. Here, a genotyping-by-sequencing (GBS) approach was used to examine genomic variation in an early life stage (megalopae) of the Dungeness crab (Cancer magister), which constitutes the most valuable single-species commercial fishery in the CCE. Variation in abundance and timing of megalopae recruitment has been extensively studied for over two decades in Coos Bay, Oregon, United States. Within the CCE, documented timing of Dungeness crab life history events indicates that coastal megalopae recruitment is expected to occur April through July; however, long-term studies in Coos Bay have observed late-season recruitment from August to October. Based on variation at 1,913 presumably neutral loci, evidence was found for weak, yet significant differentiation (FST estimate = 0.0011) between the 2014 expected-season recruits (n = 47) and late-season recruits (n = 47) collected in Coos Bay. However, two putatively adaptive loci with a high FST estimate (0.2036) between expected-season and late-season recruits were identified. These findings support the hypothesis that expected-season and late-season megalopae recruiting to Coos Bay within the same year may have originated from different locations or from different breeding groups. Understanding marine species connectivity between ecosystems is important when considering how future changes in ocean conditions may impact fishery harvests.
... The presence of all stages may also indicate high population mixing of Dungeness crab along its range. Population structure based on genetic differentiation has been found to be weak (O'Malley et al. 2017, Jackson et al. 2018. Latitudinal dispersal may be mediated by the long pelagic larval duration of Dungeness crab (80-160 days) and the relative strength of surface currents within the CCLME. ...
Proposal, manuscript, and final presentation from my 2019 NSF REU at Hatfield Marine Science Center
... In British Columbia, a fjord-like sound was clearly genetically differentiated from all other sites suggesting that the complex hydrology of inland waters may limit gene flow (Beacham et al. 2008). A second population genetic study reported similar levels of genetic diversity and little evidence of genetic population structure along the Oregon coast, yet genetic differentiation between the coast and two sites in British Columbia (O'Malley et al. 2017). Together, these studies suggest that genetic connectivity is stronger along the coast than within inland waters. ...
... We did not observe significant genetic differentiation among sites in coastal Washington. This finding is consistent with the weak differentiation reported for Dungeness crab in coastal Oregon (O'Malley et al. 2017). Given the relatively short geographic distance between coastal sampling sites, it is likely that a considerable amount of migrant exchange occurs on an annual basis. ...
Understanding connectivity of marine organisms is necessary for determining the appropriate scale of conservation and management strategies. For species that inhabit both the coastal ocean and partially enclosed water bodies (i.e., estuaries or fjords), this information is even more critical since estuaries and fjords are often characterized by hydrological complexities which can limit dispersal potential and promote population subdivision. In this study, genetic connectivity of Dungeness crab Cancer magister in Puget Sound and coastal Washington, USA, was examined to test the hypothesis of genetic structure in partially enclosed versus open environments. Dungeness crab that were sampled at five sites in Puget Sound in 2015 and three sites in coastal Washington in 2014 were genotyped at ten microsatellite loci. We observed similar levels of heterozygosity and allelic richness within Puget Sound and coastal Washington. Pairwise FST estimates indicated that Hood Canal was significantly differentiated from other Puget Sound sites, except Nisqually, suggesting larval retention within the Hood Canal basin. No evidence for significant genetic differentiation was found among the four remaining Puget Sound sites or among the three coastal sites. Analysis of molecular variance indicated that, in aggregate, Puget Sound sites significantly differed from coastal sites. On a site by site basis, we found evidence for significant differentiation between three sites in Puget Sound and coastal Washington. Based upon the observed patterns of genetic differentiation, our findings did not support our hypothesis of restricted genetic connectivity within Puget Sound, with the exception of Hood Canal. However, our results demonstrate that there is stronger genetic connectivity within Puget Sound and coastal Washington than between these two areas.
Among global coastal regions, the Northern California Current System (N-CCS) is already experiencing effects from ocean acidification and hypoxia during the summer, primarily due to the region’s seasonal upwelling, current systems, and high productivity. Oxygen, pH, and temperature conditions are expected to become more stressful with continued fossil fuel emissions under global climate change, posing a serious threat to the region’s fisheries. N-CCS fishing communities rely heavily on the economically and culturally important Dungeness crab (Metacarcinus magister). The fishery is currently sustainably managed, but potential negative impacts from changing ocean conditions on Dungeness crab life stages and populations could have adverse effects for the fishery and the communities that rely on it. To quantify the vulnerability of Dungeness crab life stages and populations to predicted future conditions, both model projections and empirical experiments need to be employed. A semi-quantitative, life stage-specific framework was adapted here to assess the vulnerability of Dungeness crab to low pH, low dissolved oxygen, and high temperature under present and future projected conditions in the seasonally dynamic N-CCS. This was achieved using a combination of regional ocean models, species distribution maps, larval transport models, a population matrix model, and a literature review. This multi-faceted approach revealed that crab vulnerability to the three climate stressors will increase in the future (year 2100) under the most intense emissions scenario, with vulnerability to low oxygen being the most severe to the N-CCS population overall. Increases in vulnerability were largely driven by the adult life stage, which contributes the most to population growth. Empirical experiments demonstrated that adult crab respiration rates increase exponentially with temperature, potentially making this life stage more susceptible to hypoxia in the future. Together, this work provides novel insights into the effects of changing ocean conditions on Dungeness crab populations, which may help inform fishery management strategies.
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 crab Cancer magister larval 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.
Using a combination of population- and individual-based analytical approaches, we provide a comprehensive examination of genetic connectivity of Dungeness crab (Cancer magister) along ~1,200 km of the California Current System (CCS). We sampled individuals at 33 sites in 2012 to establish a baseline of genetic diversity and hierarchal population genetic structure, and then assessed inter-annual variability in our estimates by sampling again in 2014. Genetic diversity showed little variation among sites or across years. In 2012, we observed
