| Summary: | In 2014, a marine heatwave infiltrated the coast of California, persisting until 2016 and causing mass marine mammal strandings, seabird die-offs, and algal blooms in the Northeastern Pacific. Periodic strandings can provide tissue samples and morphometric data, and allow us to characterize the impact of oceanographic phenomena on local populations. As top predators, the philopatric and nearshore population of harbor porpoises (Phocoena phocoena) off the California coast offered a unique opportunity to investigate impacts of the marine heatwave on trophic dynamics in the nearshore region through their frequent strandings. Samples from stranded porpoises on the central California coast, spanning 2013-2018 were used to determine changes in isotopic niche and diet composition based on δ13C and δ15N signatures. During the marine heatwave, the mean δ15N of all porpoises increased, while δ13C remained the same. Our analyses suggested that adult harbor porpoises shifted to predation on jack mackerel during the marine heatwave, while juvenile harbor porpoises expanded their niche width throughout the study period. Our research highlighted harbor porpoise sensitivity to changes in community composition, and provided insight into how climate change in the form of marine heatwaves can impact coastal ecosystems. https://doi.org/10.46569/20.500.12680/n009w774m
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