Fish Assemblage Structure Before and After a Marine Heatwave in West Hawai'i

Abstract

Coral reefs are subject to marine heatwaves caused by human-induced climate change. Long-term thermal stress can negatively affect corals and the associated marine organisms that use these areas as critical habitat. In this study, we examined coral reef resilience to climate change by analyzing changes in fish assemblages following a marine heatwave. We analyzed 11 years of subtidal video survey data in three areas in West Hawai'i, capturing a marine heatwave event from 2014 - 2016. Fish were counted and identified to species, then assigned to one of seven functional groups: predators, secondary consumers, planktivores, corallivores, scrapers, grazers and browsers. Our study revealed three key findings. First, we show that regardless of habitat differences and management strategy, all fish assemblages became more homogeneous after a major marine heatwave. Second, we found that only eight species drove most of the changes in functional groups across locations. Third, following the marine heatwave, fish abundance increased in the areas with fewer fishing regulations, and appeared to remain high and relatively stable in a more protected area. Understanding how marine heatwaves impact coral reef communities can guide decision-making for effective coastal management. Continued long term monitoring is necessary to evaluate disturbance impacts on the coral reef ecosystem as climate change and marine heatwaves are anticipated to continue into the future.