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 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.

Uncovering mechanisms of global ocean change effects on the Dungeness crab (Cancer magister) through metabolomics analysis

ABSTRACTThe Dungeness crab is an economically and ecologically important species distributed along the North American Pacific coast. To predict how Dungeness crab may physiologically respond to future global ocean change on a molecular level, we performed untargeted metabolomic approaches on individual Dungeness crab juveniles reared in treatments that mimicked current and projected future pH and dissolved oxygen conditions. We found 94 metabolites and 127 lipids responded in a condition-specific manner, with a greater number of known compounds more strongly responding to low oxygen than low pH exposure. Pathway analysis of these compounds revealed that juveniles may respond to low oxygen through evolutionarily conserved processes including downregulating glutathione biosynthesis and upregulating glycogen storage, and may respond to low pH by increasing ATP production. Most interestingly, we found that the response of juveniles to combined low pH and low oxygen exposure was most similar to the low oxygen exposure response, indicating low oxygen may drive the physiology of juvenile crabs more than pH. Our study elucidates metabolic dynamics that expand our overall understanding of how the species might respond to future ocean conditions and provides a comprehensive dataset that could be used in future ocean acidification response studies.

Cover letter RE “Video observations of the acute effects of dredged sediment deposition on mobile epifauna”

The “beneficial uses” of dredged sediment are increasingly being explored for habitat restoration and beach nourishment. At ocean and nearshore deposition sites, any beneficial use must be tempered by evaluating impacts to the benthos. We studied a site at the mouth of the Columbia River where a “thin-layer” sediment deposition method was employed to minimize mounding and disperse sediment within a prescribed area. We used baited benthic video landers (BVLs) in a Before-After Control-Impact (BACI) experimental design to test the acute effects of sediment deposition on the Dungeness crab (Cancer magister) and dog whelk (Nassarius spp). We considered the acute effects of both sediment deposition depths and the lateral surge (the turbidity front transiting the seafloor). Observations revealed sedimentation levels were limited (< 4 cm) and likely posed no direct threat to epifauna. Video and instrument readings showed the lateral surge to impact the BVLs as a 2 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 (5 to 7 min). Further, crabs often 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. The BVLs in a BACI experimental design were an effective means of measuring sediment impacts to mobile epifauna, and video observations were informative for understanding lateral surge dynamics and the behavioral interactions of organisms.