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MEPS prepress abstract   -  DOI:

Changes in Fish Assemblages after Marine Heatwave Events in West Hawai‘i Island

Amy Y. Olsen*, Shawn Larson, Jacqueline L. Padilla-Gamiño, Terrie Klinger

*Corresponding author:

ABSTRACT: Marine heatwaves are prolonged events of anomalously warm water that affect diverse marine habitats and their associated biota. Evidence shows that anthropogenic climate change is increasing the frequency and duration of marine heatwaves, and that coral reef systems are sensitive to the thermal stress imposed by marine heatwaves. In this study, we examined fish community response to consecutive marine heatwaves (2014-2015) by analyzing changes in fish assemblages in Hawai‘i over 11 years (2009 – 2019). Subtidal video survey data were collected in three areas on the west side of the Big Island of Hawai‘i. Fish were counted and identified to species or genus, then assigned to one of seven functional groups: predators, secondary consumers, planktivores, corallivores, scrapers, grazers and browsers. Our study revealed four key findings. We show that all fish assemblages changed significantly in each area after the marine heatwaves. Across all three areas, the three most abundant functional groups (planktivores, grazers and secondary consumers) drove the observed changes in the community. Following the marine heatwaves, fish abundance increased in two areas with fewer fishing regulations. In the most protected area, fish abundance remained high and diversity indices were significantly higher post-marine heatwaves. Our results support the hypothesis that marine heatwaves can cause shifts in fish assemblages and that the precise nature of these shifts can vary over relatively short spatial scales that may coincide with scales of management.