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

   https://doi.org/10.3354/meps13871  

   LaRoche, NL; King, SL; Rogers, MC; Eckert, GL; Pearson, HC (October 2021, Marine Ecology Progress Series)

   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 (δ 13 C) and nitrogen (δ 15 N). 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. 

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2. Southeast Alaskan kelp forests: inferences of process from large-scale patterns of variation in space and time

   https://doi.org/10.1098/rspb.2021.1697  

   Gorra, Torrey R.; Garcia, Sabrina C.; Langhans, Michael R.; Hoshijima, Umihiko; Estes, James A.; Raimondi, Pete T.; Tinker, M. Tim; Kenner, Michael C.; Kroeker, Kristy J. (January 2022, Proceedings of the Royal Society B: Biological Sciences)

   Humans were considered external drivers in much foundational ecological research. A recognition that humans are embedded in the complex interaction networks we study can provide new insight into our ecological paradigms. Here, we use time-series data spanning three decades to explore the effects of human harvesting on otter–urchin–kelp trophic cascades in southeast Alaska. These effects were inferred from variation in sea urchin and kelp abundance following the post fur trade repatriation of otters and a subsequent localized reduction of otters by human harvest in one location. In an example of a classic trophic cascade, otter repatriation was followed by a 99% reduction in urchin biomass density and a greater than 99% increase in kelp density region wide. Recent spatially concentrated harvesting of otters was associated with a localized 70% decline in otter abundance in one location, with urchins increasing and kelps declining in accordance with the spatial pattern of otter occupancy within that region. While the otter–urchin–kelp trophic cascade has been associated with alternative community states at the regional scale, this research highlights how small-scale variability in otter occupancy, ostensibly due to spatial variability in harvesting or the risk landscape for otters, can result in within-region patchiness in these community states. 

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3. Stable isotope fingerprinting traces essential amino acid assimilation and multichannel feeding in a vertebrate consumer

   https://doi.org/10.1111/2041-210X.13903  

   Manlick, Philip J.; Newsome, Seth D. (August 2022, Methods in Ecology and Evolution)

   Abstract Animals often consume resources from multiple energy channels, thereby connecting food webs and driving trophic structure. Such ‘multichannel feeding’ can dictate ecosystem function and stability, but tools to quantify this process are lacking. Stable isotope ‘fingerprints’ are unique patterns in essential amino acid (EAA) δ 13 C values that vary consistently between energy channels like primary production and detritus, and they have emerged as a tool to trace energy flow in wild systems. Because animals cannot synthesize EAAs de novo and must acquire them from dietary proteins, ecologists often assume δ 13 C fingerprints travel through food webs unaltered. Numerous studies have used this approach to quantify energy flow and multichannel feeding in animals, but δ 13 C fingerprinting has never been experimentally tested in a vertebrate consumer. We tested the efficacy of δ 13 C fingerprinting using captive deer mice Peromyscus maniculatus raised on diets containing bacterial, fungal and plant protein, as well as a combination of all three sources. We measured the transfer of δ 13 C fingerprints from diet to consumer liver, muscle and bone collagen, and we used linear discriminant analysis (LDA) and isotopic mixing models to estimate dietary proportions compared to known contributions. Lastly, we tested the use of published δ 13 C source fingerprints previously used to estimate energy flow and multichannel feeding by consumers. We found that EAA δ 13 C values exhibit significant isotopic (i.e. trophic) fractionation between consumer tissues and diets. Nevertheless, LDA revealed that δ 13 C fingerprints are consistently routed and assimilated into consumer tissues, regardless of isotopic incorporation rate. Isotopic mixing models accurately estimated the proportional diets of consumers, but all models overestimated plant‐based protein contributions, likely due to the digestive efficiencies of protein sources. Lastly, we found that δ 13 C source fingerprints from published literature can lead to erroneous diet reconstruction. We show that δ 13 C fingerprints accurately measure energy flow to vertebrate consumers across tissues with different isotopic incorporation rates, thereby enabling the estimation of multichannel feeding at various temporal scales. Our findings illustrate the power of δ 13 C fingerprinting for quantifying food web dynamics, but also reveal that careful selection of dietary source data is critical to the accuracy of this emerging technique. 

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4. Hard Rock Buffet: Chemosynthetic Carbon Use and Environmental Trophic Structuring of Carbonate‐Associated Macrofauna at Southern California Methane Seeps

   https://doi.org/10.1111/maec.70088  

   Pereira, Olívia S; Survilas, Rachel; Bravo, María Emilia; Levin, Lisa A (March 2026, Marine Ecology)

   ABSTRACT Diverse invertebrate communities inhabiting carbonate rocks at methane seeps may rely on a mix of local chemosynthetic production and sinking photosynthetic organic matter, with relative importance shaped by environmental conditions. We investigate the contribution of chemosynthetic carbon to macrofaunal diets at six Southern California methane seeps (275–1020 m depth) and the influence of seep site, seepage habitat, water depth, and oxygen on trophic structure, using stable isotope analyses, Bayesian mixing models, and generalized additive models. Macrofauna exhibit wide isotopic ranges and methane‐derived carbon (MDC) contributions, with several species deriving > 80% of their diet from chemosynthetic sources, including pyropeltid limpets, provannid snails, and dorvilleid and nereidid polychaetes. Negative δ¹⁵N values and high MDC in a trichobranchid polychaete and sponge are consistent with N₂fixation or incorporation of N‐fixing microbial biomass. Taxa historically not considered as ‘seep fauna’ (e.g., bryozoans and cnidarians) also incorporate substantial chemosynthetic input, challenging their classification as ‘background’ taxa. Community‐wide trophic structure varied strongly by seep habitat, with active seepage habitats showing higher chemosynthetic reliance, trophic diversity, and isotope ranges. Seep production export into surrounding systems was greater at deeper seeps, suggesting a stronger trophic sphere of seep influence where photosynthetic input is more limited. This increased reliance on chemosynthesis with depth appears to reverse the typical positive δ¹⁵N‐depth relationship observed in non‐chemosynthetic fauna. Low oxygen seems to favor a restricted number of species with specialized trophic niches. Macrofauna isotopic variability across seep sites likely reflects differences in fluid flux regime and geochemistry. Our study demonstrates that chemosynthetic production plays a broad role in supporting the deep‐sea communities off Southern California and reveals complex, and potentially novel, trophic interactions at methane seeps. These findings underscore the importance of incorporating trophic diversity and associated functional heterogeneity in conservation planning, especially as environmental changes reshape deep‐sea ecosystems, warranting more nuanced protection frameworks. 

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5. Juvenile Chum Salmon and Pink Salmon use of submerged vegetative habitats and the influence of an apex predator

   https://doi.org/10.1093/mcfafs/vtaf001  

   Domke, Lia K; Cates, Rebecca J; Raymond, Wendel W; Eckert, Ginny L (March 2025, Marine and Coastal Fisheries)

   ABSTRACT ObjectiveApex-predator-initiated trophic cascades occur in many nearshore marine habitats that simultaneously serve as critical habitat and food sources for commercially and ecologically important species, including juvenile Pacific salmon Oncorhynchus spp. Yet the potential relationships among apex predators (e.g., sea otters Enhydra lutris), submerged aquatic vegetation, and juvenile salmonids are not well understood. In Southeast Alaska, we investigated (1) juvenile salmonid abundance in eelgrass Zostera marina meadows and understory kelp beds and (2) potential drivers of juvenile Chum Salmon Oncorhynchus keta and Pink Salmon O. gorbuscha abundance in eelgrass meadows. MethodsWe analyzed historic (1998–2007) beach seine surveys to compare juvenile salmonid abundance in nearshore habitats. We then employed the same survey (2017, 2019) in eelgrass to quantify juvenile salmonid abundance alongside the influence of sea otter density (number/km2), distance from anadromous stream (km), seasonality, sediment categorization, and aboveground eelgrass biomass (g/m2). ResultsWe found greater abundance of Chum Salmon in understory kelp compared with eelgrass, whereas Pink Salmon abundance was similar between habitats. In eelgrass, Chum Salmon abundance peaked in June and was positively associated with sea otter density. Pink Salmon abundance varied seasonally, peaking in May. We found increased Pink Salmon abundance with increasing sea otter density and distance from anadromous stream and decreased abundance with increased eelgrass biomass. ConclusionGrowth and survival while juvenile salmonids are out-migrating from streams and relying on nearshore vegetated habitats can determine if they recruit to fisheries as adults. Here, we highlight the use of multiple habitats, eelgrass and understory kelp, indicating that both should be explored as critical nursery habitat. We present evidence of indirect effects of sea otters influencing the abundance of juvenile salmonids, with potential further implications as sea otter populations expand. Apex predators, quality of vegetated habitats, and their structuring roles in the nearshore are critical for informing adaptive coastal fisheries management. 

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