Aaron W. E. Galloway

The effects of winter environmental conditions on lake ecology can be highly variable. Ice and overlying snow isolate the water below, impeding exchange of materials among water, atmosphere, and the watershed. Even with these limitations, biological communities under the ice can persist, where cold‐tolerant taxa can be especially abundant. Because many under‐ice taxa tend to have a suite of unsaturated lipids that enable them to maintain metabolic function during cold conditions, under‐ice biological communities may contain highly nutritious resources for higher level consumers relative to warmer, open‐water conditions. To examine the effects of ice presence on under‐ice biological productivity and nutritional quality, we aggregated data on under‐ice physical, chemical, and biological variables from several existing databases. These data are among the most comprehensive, publicly available environmental and phytoplankton data that can be used to compare under‐ice and open‐water conditions at the community level. To understand how phytoplankton compositional shifts under ice can precipitate shifts in total algal nutritional content available to consumers relative to open‐water conditions, we merged characteristic phytoplankton fatty acid profiles with phytoplankton community composition data. Our results suggest that even though photosynthetically active radiation under ice is dramatically reduced by snow cover and opaque ice conditions, algal communities can be highly productive. Furthermore, these under‐ice communities tend to be dominated by cold‐water taxa, which are associated with elevated essential polyunsaturated fatty acids and reduced saturated fatty acids. Saturated fatty acids tend to be most associated with phytoplankton communities in the summer when cyanobacteria are prevalent, while winter communities tend to be most associated with high polyunsaturated fatty acids. As ice duration and quality continue to shift with increasing temperatures worldwide, phytoplankton assemblages are likely to exhibit altered nutritional profiles that have direct and indirect effects on food webs.

Kelp forest degradation is accelerating globally due to marine heatwaves, climate stressors, and persistent overgrazing by sea urchins, creating an urgent need for restoration strategies that rebuild ecosystem function. Yet, how restored kelp subsidies translate into improved food quality and consumer condition, core indicators of trophic recovery, remains poorly quantified. We combined fatty acid biomarkers with a Before–After–Control–Impact Paired Series (BACIPS) experiment to evaluate how targeted urchin removals in Haida Gwaii, British Columbia, altered the nutritional landscape for two ecologically and culturally important grazers: red sea urchins ( Mesocentrotus franciscanus ) and northern abalone ( Haliotis kamtschatkana ). One year after restoration, bull kelp ( Nereocystis luetkeana ) increased ~67‐fold in shallow strata, while deep kelp biomass rose from 0 to 9.08 stipes/60 m ² (±4.52 SE), coinciding with marked increases in kelp‐associated fatty acids and improved gonad mass in urchins. In abalone, fatty acid profiles revealed a size‐dependent dietary shift in which larger individuals assimilated more kelp, and levels of essential fatty acids increased across both species following kelp recovery. These results provide depth‐resolved, field‐based evidence that kelp restoration enhances food quality and consumer condition in degraded habitats. Synthesis and applications . Fatty acid biomarkers offer a scalable tool for detecting early trophic recovery, identifying high‐leverage depth strata for intervention, and evaluating whether restoration actions are rebuilding the ecosystem functions and fisheries‐relevant nutritional pathways that support resilient kelp forest ecosystems.

Many heterotroph species perish when faced with severe food limitation; others can persist, adapt, and thrive. Sea urchins are emblematic of this paradox: they can overgraze kelp forests to form barren habitats, but can then survive for decades in these nutritionally depauperate seascapes. Understanding the mechanisms enabling persistence under starvation and rapid recovery when food returns provides insights into how consumer resilience shapes ecosystem dynamics. We quantified how food abundance, quality, deprivation, and reintroduction influence bioenergetic performance in the red sea urchin ( Mesocentrotus franciscanus ), integrating field observations of kelp forest and barren populations with a controlled feeding experiment. We measured respiration, feeding rates, gonadal growth, and fatty acid biomarkers to test how habitat history and diet jointly govern metabolic plasticity and nutrient assimilation. Resting metabolic rates (RMRs) were nearly twofold higher in kelp forest urchins than in barren conspecifics; yet, feeding rates were equivalent across habitats, indicating that metabolic depression does not constrain food intake. Reciprocal shifts emerged in the experiment: starvation reduced RMR and lipid reserves in kelp forest urchins, while feeding elevated both traits in barren urchins to levels comparable with kelp forest conspecifics. These results demonstrate rapid physiological compensation in response to both food deprivation and reintroduction. Diet quality strongly modulated performance. Urchins fed nutritionally poor monospecific diets consumed more biomass and calories than those on diverse, polyunsaturated fatty acid (PUFA)‐rich diets, but did so with markedly lower efficiency of conversion to gonadal tissue. Fatty acid assimilation revealed that starvation elevated bacterial and biofilm biomarkers in tissues, whereas algal diets enriched essential PUFA profiles, particularly when diets were diverse. These results highlight that both quantity and quality of food influence consumer recovery trajectories, with nutritional geometry shaping efficiency of energy and nutrient use. Together, our findings show that M. franciscanus exhibits pronounced metabolic resilience, allowing persistence in barren habitats and rapid reactivation of grazing and reproduction when food becomes available. This work links nutritional ecology to ecosystem feedbacks by showing how compensatory feeding and metabolic flexibility enable consumers to maintain pressure on primary producers, thereby influencing the stability, hysteresis, and recovery of degraded ecosystems.

Within the highly productive Northern California Current (NCC) ecosystem, the ctenophore Pleurobrachia bachei is common, yet its trophic role remains unclear. Samples of P. bachei were collected from the NCC in 2018–2019 at two latitudes, including the Newport Hydrographic Line and Trinidad, during two seasons (summer and winter). Samples were dissected for gut contents and analyzed for fatty acid concentrations. The three most abundant prey categories found within P. bachei guts were consistently adult copepods, copepod eggs, and invertebrate eggs, although the relative contribution of these and other prey varied significantly between seasons and latitudes. Essential fatty acids, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) together made up nearly half of P. bachei fatty acid content. While this sum was consistent through space and time, EPA and DHA individually varied. Patterns in both P. bachei predation and fatty acid content track seasonal and latitudinal variability in this highly dynamic eastern boundary upwelling system, with seasons driving slightly larger differences. Our analyses suggest that P. bachei in the NCC acts as both an influential predator and an important prey source, highlighting the need to include P. bachei and other underappreciated gelatinous zooplankton in modeling of pelagic food webs.

Predator loss can cause shifts in ecosystem state, especially when accompanied by changes in the behaviour of its prey. The recent decline of predatory sunflower sea stars Pycnopodia helianthoides and a coincident a decline of kelp forests across the northeastern Pacific raises questions about their role in kelp forest ecosystem maintenance and recovery. While P. helianthoides may support kelp forests by consuming herbivorous sea urchins, less is known about their non-consumptive effects, especially in degraded habitats. Here, we ask: How do the non-consumptive effects of this predator vary among prey species, and what are the emergent effects on community-level grazing pressure in a degraded habitat when kelp is reintroduced? We conducted a field experiment, where we deployed kelp blades in urchin barrens at discrete distances from caged P. helianthoides and control cages for 24 h. We demonstrate a reduction in the density of red sea urchins Mesocentrotus franciscanus nearest the sunflower star and no effect on green sea urchins Strongylocentrotus droebachiensis . Our results suggest the chemical cue of P. helianthoides elicits a localized landscape of fear of approximately 15 m ² that suppresses grazing, and that the non-consumptive effects of P. helianthoides on sea urchin behaviour may be important for kelp restoration.

Many heterotroph species perish when faced with severe food limitation, others can persist, adapt, and thrive. Sea urchins are emblematic of this paradox: they can overgraze kelp forests to form barren habitats, but can then survive for decades in these nutritionally depauperate seascapes. Understanding the mechanisms enabling persistence under starvation, and rapid recovery when food returns, provides insight into how consumer resilience shapes ecosystem dynamics. We quantified how food abundance, quality, deprivation, and reintroduction influence bioenergetic performance in the red sea urchin ( Mesocentrotus franciscanus ), integrating field observations of kelp forest and barren populations with a controlled feeding experiment. We measured respiration, feeding rates, gonadal growth, and fatty acid biomarkers to test how habitat history and diet jointly govern metabolic plasticity and nutrient assimilation. Resting metabolic rates (RMR) were nearly twofold higher in kelp forest urchins than barrens conspecifics, yet feeding rates were equivalent across habitats, indicating that metabolic depression does not constrain food intake. Reciprocal shifts emerged in the experiment: starvation reduced RMR and lipid reserves in kelp forest urchins, while feeding elevated both traits in barrens urchins to levels comparable with kelp forest conspecifics. These results demonstrate rapid physiological compensation in response to both food deprivation and reintroduction. Diet quality strongly modulated performance. Urchins fed nutritionally poor monospecific diets consumed more biomass and calories than those on diverse, polyunsaturated fatty acid (PUFA)-rich diets, but did so with markedly lower efficiency of conversion to gonadal tissue. Fatty acid assimilation revealed that starvation elevated bacterial and biofilm biomarkers in tissues, whereas algal diets enriched essential PUFA profiles, particularly when diets were diverse. These results highlight that both quantity and quality of food influence consumer recovery trajectories, with nutritional geometry shaping efficiency of energy and nutrient use. Together, our findings show that M. franciscanus exhibits pronounced metabolic resilience, allowing persistence in barren habitats and rapid reactivation of grazing and reproduction when food becomes available. This work links nutritional ecology to ecosystem feedbacks by showing how compensatory feeding and metabolic flexibility enable consumers to maintain pressure on primary producers, thereby influencing the stability, hysteresis, and recovery of degraded ecosystems.

Changes in the seasonal environment substantially influence organisms. Understanding how species respond to such changes, such as in their feeding interactions and physiology, is key to predicting their resilience to both seasonal and longer term climate changes. The Sitka Sound in Southeast Alaska, USA, is an attractive natural laboratory for studying change, as the marine environment experiences substantial seasonal fluctuations in parameters such as temperature, pH, and productivity between summer and winter. By sampling a suite of dominant macrophyte algae and their benthic herbivores in winter (January) and summer (July) 2019, we investigated how producers and their primary consumers may respond to seasonal change inferred through fatty acid trophic markers. We used a fatty acid logratio selection and analysis approach to ask the following: (1) Do fatty acid biomarkers for algae differ between seasons? (2) Do the same fatty acid biomarkers differ between seasons when applied to herbivores, with herbivore fatty acids tracking the presumed trophic resources? (3) Do fatty acid biomarkers for herbivores differ between seasons, when considered independently from algae? Comparing logratio sets selected each for the algae and the herbivore fatty acids, we found that algae fatty acids were different between our sampling seasons, but the algae‐selected fatty acid logratios did not clearly separate most herbivores by season. In contrast, the herbivore‐selected logratios strongly distinguished herbivore species between the January and June samplings. Further, dispersions of fatty acid logratios were greater within herbivore species in the winter than in the summer, potentially due to the utilization of more diverse resources when preferred algae are less abundant. In total, results suggest that herbivores are not simply tracking the seasonal fatty acid changes in the dominant algae as trophic resources; instead, herbivore fatty acid seasonal changes may occur largely through some other nonexclusive mechanisms, such as omnivory, reductions or shifts in dietary composition, and/or endogenous physiological responses. Thus, the benthic herbivores in our study appear not to be locked into their diets when faced with seasonal change and may use a range of strategies, including diet diversification, to cope with environmental variation.

Sea ice can profoundly influence photosynthetic organisms by altering subsurface irradiance, but it is susceptible to changes in the climate. The patterns and timing of sea ice cover can vary on a monthly to annual timescale in small sub‐regions of the Western Antarctic Peninsula (WAP). During the latter part of the 20th century, sea ice coverage significantly decreased in the WAP, a trend that aligns with warming in this area. Macroalgal biochemical components are impacted by light availability, often showing a close relationship between photosynthesis and biochemical compositions. We used satellite imagery of annual sea ice duration and extent as well as water turbidity during ice‐free periods to identify 14 study sites that differed dramatically in sea ice coverage but were similar in terms of turbidity along the central WAP between 68° S and 64° S. The common macroalgal species Desmarestia menziesii, Himantothallus grandifolius, Sarcopeltis antarctica, and Iridaea sp. were collected by scuba divers between 5 m and 35 m depth at each site where they occurred, for later biochemical analyses. Overall percentages of major biochemical components as well as carbon and nitrogen percentages and C:N were determined and correlated with four different sea ice indices. Surprisingly, most of the chemical components were not significantly correlated with sea ice cover. The few significant correlations varied between species and chemical components. This indicates that although patterns of sea ice coverage have major implications for macroalgal abundance, on a per‐biomass basis, sea ice coverage does not impact the nutritional contributions of macroalgae to food webs.