Search for: All records

Abstract Variability in primary producers' responses to environmental change may buffer higher trophic levels against shifts in basal resource composition. Then again, in instances where there is a lack of functional redundancy because consumers rely on a few species to meet their energetic requirements at specific times of the year, altered community production dynamics may significantly impact food web resilience. In high‐latitude kelp forests, a complementary annual phenology of seaweed production supports coastal marine consumers' metabolic needs across large seasonal variations in their environment. Yet, marine consumers in these systems may face significant metabolic stress under the pronounced low pH conditions expected in future winters, particularly if they lack the resources to support their increased energetic demands. In this study, we investigate how the growth and nutritional value of three dominant, coexisting macroalgal species found in subpolar kelp forests will respond to ocean acidification and warming in future winter and summer seasons. We find that the three kelpsMacrocystis pyrifera,Hedophyllum nigripes, andNeoagarum fimbriatumdiffer in their vulnerability to future environmental conditions, and that the seasonal environmental context of nutrient and light availability shapes these responses. Our results suggest that poleward fringe populations ofM. pyriferamay be relatively resilient to anticipated ocean warming and acidification. In contrast, ocean warming conditions caused a decrease in the biomass and nutritional quality of both understory kelps. Considering the unique production phenology ofH. nigripes, we emphasize that negative impacts on this species in future winters may be of consequence to consumer energetics in this system. This work highlights how interspecific variation in autotrophs' responses to global change can disrupt the diversity and phenological structure of energy supply available to higher trophic levels. 

Abstract It is well understood that differences in the cues used by consumers and their resources in fluctuating environments can give rise to trophic mismatches governing the emergent effects of global change. Trophic mismatches caused by changes in consumer energetics during periods of low resource availability have received far less attention, although this may be common for consumers during winter when primary producers are limited by light. Even less is understood about these dynamics in marine ecosystems, where consumers must cope with energetically costly changes in CO₂‐driven carbonate chemistry that will be most pronounced in cold temperatures. This may be especially important for calcified marine herbivores, such as the pinto abalone (Haliotis kamschatkana).H. kamschatkanaare of high management concern in the North Pacific due to the active recreational fishery and their importance among traditional cultures, and research suggests they may require more energy to maintain their calcified shells and acid/base balance with ocean acidification. Here we use field surveys to demonstrate seasonal mismatches in the exposure of marine consumers to low pH and algal resource identity during winter in a subpolar, marine ecosystem. We then use these data to test how the effects of exposure to seasonally relevant pH conditions onH. kamschatkanaare mediated by seasonal resource identity. We find that exposure to projected future winter pH conditions decreases metabolism and growth, and this effect on growth is pronounced when their diet is limited to the algal species available during winter. Our results suggest that increases in the energetic demands of pinto abalone caused by ocean acidification during winter will be exacerbated by seasonal shifts in their resources. These findings have profound implications for other marine consumers and highlight the importance of considering fluctuations in exposure and resources when inferring the emergent effects of global change. 

Abstract The environmental conditions in the ocean have long been considered relatively more stable through time compared to the conditions on land. Advances in sensing technologies, however, are increasingly revealing substantial fluctuations in abiotic factors over ecologically and evolutionarily relevant timescales in the ocean, leading to a growing recognition of the dynamism of the marine environment as well as new questions about how this dynamism may influence species' vulnerability to global environmental change. In some instances, the diurnal or seasonal variability in major environmental change drivers, such as temperature, pH and seawater carbonate chemistry, and dissolved oxygen, can exceed the changes expected with continued anthropogenic global change. While ocean global change biologists have begun to experimentally test how variability in environmental conditions mediates species' responses to changes in the mean, the extensive literature on species' adaptations to temporal variability in their environment and the implications of this variability for their evolutionary responses has not been well integrated into the field. Here, we review the physiological mechanisms underlying species' responses to changes in temperature,pCO₂/pH (and other carbonate parameters), and dissolved oxygen, and discuss what is known about behavioral, plastic, and evolutionary strategies for dealing with variable environments. In addition, we discuss how exposure to variability may influence species' responses to changes in the mean conditions and highlight key research needs for ocean global change biology. 

Production rates reported for canopy‐forming kelps have highlighted the potential contributions of these foundational macroalgal species to carbon cycling and sequestration on a globally relevant scale. Yet, the production dynamics of many kelp species remain poorly resolved. For example, productivity estimates for the widely distributed giant kelpMacrocystis pyriferaare based on a few studies from the center of this species' range. To address this geospatial bias, we surveyed giant kelp beds in their high latitude fringe habitat in southeast Alaska to quantify foliar standing crop, growth and loss rates, and productivity ofM. pyriferaand co‐occurring understory kelpsHedophyllum nigripesandNeoagarum fimbriatum. We found that giant kelp beds at the poleward edge of their range produce ~150 g C · m⁻²· year⁻¹from a standing biomass that turns over an estimated 2.1 times per year, substantially lower rates than have been observed at lower latitudes. Although the productivity of high latitudeM. pyriferadwarfs production by associated understory kelps in both winter and summer seasons, phenological differences in growth and relative carbon and nitrogen content among the three kelp species suggests their complementary value as nutritional resources to consumers. This work represents the highest latitude consideration ofM. pyriferaforest production to date, providing a valuable quantification of kelp carbon cycling in this highly seasonal environment. 

Acidification‐induced changes in neurological function have been documented in several tropical marine fishes. Here, we investigate whether similar patterns of neurological impacts are observed in a temperate Pacific fish that naturally experiences regular and often large shifts in environmental pH/pCO₂. In two laboratory experiments, we tested the effect of acidification, as well as pH/pCO₂variability, on gene expression in the brain tissue of a common temperate kelp forest/estuarine fish,Embiotoca jacksoni. Experiment 1 employed static pH treatments (target pH = 7.85/7.30), while Experiment 2 incorporated two variable treatments that oscillated around corresponding static treatments with the same mean (target pH = 7.85/7.70) in an eight‐day cycle (amplitude ± 0.15). We found that patterns of global gene expression differed across pH level treatments. Additionally, we identified differential expression of specific genes and enrichment of specific gene sets (GSEA) in comparisons of static pH treatments and in comparisons of static and variable pH treatments of the same mean pH. Importantly, we found that pH/pCO₂variability decreased the number of differentially expressed genes detected between high and low pH treatments, and that interindividual variability in gene expression was greater in variable treatments than static treatments. These results provide important confirmation of neurological impacts of acidification in a temperate fish species and, critically, that natural environmental variability may mediate the impacts of ocean acidification. 

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. 

Marine ecosystems are increasingly impacted by global environmental changes, including warming temperatures, deoxygenation, and ocean acidification. Marine scientists recognize intuitively that these environmental changes are translated into community changes via organismal physiology. However, physiology remains a black box in many ecological studies, and coexisting species in a community are often assumed to respond similarly to environmental stressors. Here, we emphasize how greater attention to physiology can improve our ability to predict the emergent effects of ocean change. In particular, understanding shifts in the intensity and outcome of species interactions such as competition and predation requires a sharpened focus on physiological variation among community members and the energetic demands and trophic mismatches generated by environmental changes. Our review also highlights how key species interactions that are sensitive to environmental change can operate as ecological leverage points through which small changes in abiotic conditions are amplified into large changes in marine ecosystems.