Behavioral observations and stable isotopes reveal high individual variation and little seasonal variation in sea otter diets in Southeast Alaska

Two complementary approaches were used to assess year-round variation in the diet of sea otters Enhydra lutris around Prince of Wales Island (POW) in southern Southeast Alaska, a region characterized by mixed-bottom habitat. We observed sea otters foraging to determine diet composition during the spring and summer. Then, we obtained sea otter vibrissae, which record temporal foraging patterns as they grow, from subsistence hunters to identify year-round changes in sea otter diets via stable isotope analysis of carbon (δ13C) and nitrogen (δ15N). We compared the stable isotopes from sea otter vibrissae and sea otter prey items that were collected during spring, summer, and winter. Overall, year-round sea otter diet estimates from stable isotope signatures and visual observations from spring and summer were dominated by clams in terms of biomass, with butter clams Saxidomus gigantea the most common clam species seen during visual observations. Our results indicate that these sea otters, when considered together at a regional level around POW, do not exhibit shifts in the main prey source by season or location. However, sea otter diets identified by stable isotopes had a strong individual-level variation. Behavioral variation among individual sea otters may be a primary driving factor in diet composition. This study provides quantitative diet composition data for modeling predictions of invertebrate population estimates that may aid in the future management of shellfisheries and subsistence hunting and the development of co-management strategies for this protected species.Sea otter vibrissae were collected with help from the US Fish and Wildlife Service sea otter tagging program, specifically Brad Benter and Michelle Kissling, and Algeron Frisby, Theodore Peele, Vaughn Skinna, and the Sea Otter Commission, specifically Dennis Nickerson. We thank Ashley Bolwerk, Maggie Shields, Melanie Borup, Tiffany Stephens, Wendel Raymond, Lia Domke, Sarah Peele, Franz Mueter, Dan Monson, Todd Miller, Emily Fergusson, Corey Fugate, and Robert Bradshaw for field, lab, and analysis assistance. This work was a part of N.L.L.’s Master’s thesis at the University of Alaska Fairbanks (UAF). We were funded by the National Science Foundation (NSF) Coastal SEES (Science, Engineering and Education for Sustainability, award no. 1600049), NSF Bio-Oce (Biological Oceanography, award no. 1600230), National Oceanic and Atmospheric Administration, National Marine Fisheries Ser - vice, Auke Bay Laboratories (ABL), and Earthwatch Institute. This publication is the result of research sponsored by the Cooperative Institute for Alaska Research with funds from NOAA under cooperative agreement NA13OAR 4320056 with the University of Alaska. S.L.K. was supported by BLaST at UAS, which is supported by the NIH Common Fund, through the Office of Strategic Coordination, Office of the NIH Director with the linked awards: TL4GM118992, RL5GM118990, and UL1GM118991. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.Ye

Sea otter effects on trophic structure of seagrass communities in southeast Alaska

Previous research in southeast Alaska on the effects of sea otters Enhydra lutris in seagrass Zostera marina communities identified many but not all of the trophic relationships that were predicted by a sea otter-mediated trophic cascade. To further resolve these trophic connections, we compared biomass, carbon (δ13C) and nitrogen (δ15N) stable isotope (SI), and fatty acid (FA) data from 16 taxa at 3 sites with high and 3 sites with low sea otter density (8.2 and 0.1 sea otters km−2, respectively). We found lower crab and clam biomass in the high sea otter region but did not detect a difference in biomass of other seagrass community taxa or the overall community isotopic niche space between sea otter regions. Only staghorn sculpin differed in δ13C between regions, and Fucus, sugar kelp, butter clams, dock shrimp, and shiner perch differed in δ15N. FA analysis indicated multivariate dissimilarity in 11 of the 15 conspecifics between sea otter regions. FA analysis found essential FAs, which consumers must obtain from their diet, including 20:5ω3 (EPA) and 22:6ω3 (DHA), were common in discriminating conspecifics between sea otter regions, suggesting differences in consumer diets. Further FA analysis indicated that many consumers rely on diverse diets, regardless of sea otter region, potentially buffering these consumers from sea otter-mediated changes to diet availability. While sea otters are major consumers in this system, further studies are needed to understand the mechanisms responsible for the differences in biomarkers between regions with and without sea ottersWe thank Tiffany Stephens, Maggie Shields, Melanie Borup, Ashely Bolwerk, Nicole LaRoche, Tom Bell, Michael Stekoll and the rest of the Apex Predators, Ecosystems and Community Sustainability (APECS) team and 26 Earthwatch volunteers for assistance in the field and laboratory. Special thanks to Reyn Yoshioka, Natalie Thompson, the Coastal Trophic Ecology Lab, and Oregon Institute of Marine Biology for their assistance with fatty acid extractions, Melissa Rhodes-Reese at University of Alaska Southeast for water nutrient analysis, and Matthew Rogers and NOAA Auke Bay Laboratories for assistance with stable isotope analyses. This study was funded by the National Science Foundation (NSF #1635716, #1600230 to G.L.E.), through the generous support of Earthwatch, and a 56 NSF Graduate Research Fellowship, a North Pacific Re - search Board Graduate Student Research Award, an American Fisheries Society Steven Berkeley Marine Conservation Fellowship, and a Lerner Gray Memorial Fund (to W.W.R). This study was completed in partial fulfillment of the requirements for W.W.R.’s PhD at the University of Alaska Fairbanks and we thank committee members Dr. Franz Mueter and Dr. Anne Beaudreau for their comments on this project and the manuscript. Finally, we thank the 3 anonymous reviewers whose comments greatly improved the manuscript. This study was conducted on the traditional lands and waters of the Alaska Native Tlingit and Haida peoples. We are grateful for our access to these spaces and benefited from conversations and support from the members of Tribal communities and governments.Ye

Total Lipids, Lipid Classes, and Fatty Acids of Newly Settled Red King Crab (Paralithodes camtschaticus): Comparison of hatchery-cultured and wild crabs

Little is known about the nutrition or lipid metabolism of cold-water crabs, particularly in the North Pacific. We undertook a 2-part study to understand more completely the energetics and nutritional requirements of juvenile red king crab (RKC; Paralithodes canusehaticus). First, we investigated changes in proximate composition, total lipids (TLs), lipid classes, and fatty acids (FAs) throughout a molt cycle (C4-C5). Trends in lipid parameters were described by a 3-pari, piecewise linear regression with 3 distinct stages: (I) a postmolt phase (similar to 0-7 days), (2) an intramolt stage (similar to 7-24 days), and (3) a premolt stage (similar to 24-33 days). Significant intramolt differences in TLs indicated that caution should be taken when comparing crabs of unknown molt stage in future aquaculture and ecological experiments. However, little variability was found in the proportional FA composition of crabs, indicating that the intramolt stage has little effect on the interpretation of FA biomarkers. During a second investigation, we examined differences in lipid classes and FAs from cultured and wild RKC. We found significantly higher proportions of the essential fatty acids (EFAs) 20:5n-3 (EPA) and 20:4n-6 (AA) in wild crabs compared with cultured animals at the same stage. Furthermore, higher proportions of bacterial markers and lower proportions of zooplankton FA markers were found in wild than in hatchery-reared crabs. Here, we provide the first baseline data for future dietary studies on juvenile cold-water crabs. We suggest that an initial EFA ratio for DHA:EPA:AA of 5:8:1 could be used as a starting point for controlled dietary studies on the effect of EFAs on juvenile growth, molt success, and survival.Keywords: Lipids, Nutrition, Red king crab, Paralithodes camtschaticus, Fatty acids, Mol

Low-Altitude UAV Imaging Accurately Quantifies Eelgrass Wasting Disease From Alaska to California

Declines in eelgrass, an important and widespread coastal habitat, are associated with wasting disease in recent outbreaks on the Pacific coast of North America. This study presents a novel method for mapping and predicting wasting disease using Unoccupied Aerial Vehicle (UAV) with low-altitude autonomous imaging of visible bands. We conducted UAV mapping and sampling in intertidal eelgrass beds across multiple sites in Alaska, British Columbia, and California. We designed and implemented a UAV low-altitude mapping protocol to detect disease prevalence and validated against in situ results. Our analysis revealed that green leaf area index derived from UAV imagery was a strong and significant (inverse) predictor of spatial distribution and severity of wasting disease measured on the ground, especially for regions with extensive disease infection. This study highlights a novel, efficient, and portable method to investigate seagrass disease at landscape scales across geographic regions and conditions

Disease surveillance by artificial intelligence links eelgrass wasting disease to ocean warming across latitudes

Ocean warming endangers coastal ecosystems through increased risk of infectious disease, yet detection, surveillance, and forecasting of marine diseases remain limited. Eelgrass (Zostera marina) meadows provide essential coastal habitat and are vulnerable to a temperature-sensitive wasting disease caused by the protist Labyrinthula zosterae. We assessed wasting disease sensitivity to warming temperatures across a 3500 km study range by combining long-term satellite remote sensing of ocean temperature with field surveys from 32 meadows along the Pacific coast of North America in 2019. Between 11% and 99% of plants were infected in individual meadows, with up to 35% of plant tissue damaged. Disease prevalence was 3× higher in locations with warm temperature anomalies in summer, indicating that the risk of wasting disease will increase with climate warming throughout the geographic range for eelgrass. Large-scale surveys were made possible for the first time by the Eelgrass Lesion Image Segmentation Application, an artificial intelligence (AI) system that quantifies eelgrass wasting disease 5000× faster and with comparable accuracy to a human expert. This study highlights the value of AI in marine biological observing specifically for detecting widespread climate-driven disease outbreaks.This work was supported by the National Science Foundation (awards OCE-1829921, OCE-1829922, OCE-1829992, OCE-1829890). This is contribution 104 from the Smithsonian's MarineGEO and Tennenbaum Marine Observatories Network.Peer reviewe

Appendix A. Data used in analyses of population variability of marine invertebrates.

Data used in analyses of population variability of marine invertebrates

Appendix F. Typical water column distribution data of nearshore and shelf/slope fish larvae.

Typical water column distribution data of nearshore and shelf/slope fish larvae

Appendix B. A summary of data on the life history traits of nearshore and shelf/slope benthic crustacean species.

A summary of data on the life history traits of nearshore and shelf/slope benthic crustacean species

Appendix A. A summary of data on the life history traits of nearshore and shelf/slope fish species.

A summary of data on the life history traits of nearshore and shelf/slope fish species