Ontogeny influences sensitivity to climate change stressors in an endangered fish.
Coastal ecosystems are among the most human-impacted habitats globally, and their management is often critically linked to recovery of declining native species. In the San Francisco Estuary, the Delta Smelt (Hypomesus transpacificus) is an endemic, endangered fish strongly tied to Californian conservation planning. The complex life history of Delta Smelt combined with dynamic seasonal and spatial abiotic conditions result in dissimilar environments experienced among ontogenetic stages, which may yield stage-specific susceptibility to abiotic stressors. Climate change is forecasted to increase San Francisco Estuary water temperature and salinity; therefore, understanding the influences of ontogeny and phenotypic plasticity on tolerance to these critical environmental parameters is particularly important for Delta Smelt and other San Francisco Estuary fishes. We assessed thermal and salinity limits in several ontogenetic stages and acclimation states of Delta Smelt, and paired these data with environmental data to evaluate sensitivity to climate-change stressors. Thermal tolerance decreased among successive stages, with larval fish exhibiting the highest tolerance and post-spawning adults having the lowest. Delta Smelt had limited capacity to increase tolerance through thermal acclimation, and comparisons with field temperature data revealed that juvenile tolerance limits are the closest to current environmental conditions, which may make this stage especially susceptible to future climate warming. Maximal water temperatures observed in situ exceeded tolerance limits of juveniles and adults. Although these temperature events are currently rare, if they increase in frequency as predicted, it could result in habitat loss at these locations despite other favourable conditions for Delta Smelt. In contrast, Delta Smelt tolerated salinities spanning the range of expected environmental conditions for each ontogenetic stage, but salinity did impact survival in juvenile and adult stages in exposures over acute time scales. Our results underscore the importance of considering ontogeny and phenotypic plasticity in assessing the impacts of climate change, particularly for species adapted to spatially and temporally heterogeneous environments.
Department of Wildlife, Fish & Conservation Biology, University of California, Davis, Davis, CA 95616, USA.
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Komoroske
Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA.
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Connon
Fish Conservation and Culture Facility, University of California, Davis, Davis, CA 95616, USA.
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J
Lindberg
Department of Environmental Science and Policy, University of California, Davis, Davis, CA 95616, USA.
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BS
Cheng
United States Fish and Wildlife Service, Lodi, CA 95240, USA.
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Castillo
Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA; Aquatic Systems Biology Unit, Department of Ecology and Ecosystem Management, Technische Universität München, Muehlenweg 22, D-85354 Freising, Germany.
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Hasenbein
Department of Wildlife, Fish & Conservation Biology, University of California, Davis, Davis, CA 95616, USA.
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Fangue
Conservation management; estuarine fishes; salinity tolerance; thermal tolerance