Collaborative Research: RAPID: Turning up the heat: El Nino warming effects on top-down control of Tropical Eastern Pacific reef communities

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Species interactions are key drivers shaping marine biodiversity. Recent marine studies demonstrate that predation can be stronger at lower latitudes where water temperatures are higher. With a changing climate, it is important to resolve how environmental forces intensify or moderate consumer interactions and change the distribution and abundance of marine species. Researchers are employing a rapid research response to measure how an extreme event, the 2023-2024 El Niño, will alter consumer interactions on Tropical Eastern Pacific (TEP) coral reefs. Following up on two consecutive years of experimental data during non-El Niño conditions, they will be able to compare how an extreme event and increased ocean temperatures alter predation and herbivory rates and how this in turn influences marine biodiversity and potential invasion by non-native species. The project builds international research and education by training early-career researchers in marine science including those from under-represented groups. The project develops partnerships and fosters collaboration through an international network, which facilitates shared and integrated marine biosecurity solutions across the Americas, informing management of invasive marine species.Growing evidence suggests that the intensity of interspecific interactions increases at low latitudes. Recent studies along both coasts of the Americas indicate that the strength of consumer effects across latitude increases with temperature, consistent with the metabolic theory of ecology. The hypothesized impact of ocean warming on future trends in top-down control of marine communities predicts that increasing ocean temperatures will increase top-down control by consumers, but the extent to which this will occur in the tropics remains uncertain. The strong spatial and seasonal variation in upwelling that affect both temperature and nutrients in the Tropical Eastern Pacific (TEP) make it an ideal region to test how changes in environmental conditions influence trophic interactions and marine community dynamics. For the past two years, researchers conducted consumer exclusion experiments on sessile marine invertebrate communities at ten coral reef sites, distributed along a gradient of upwelling activity in Panama and Costa Rica. By comparing replicated caged (predator exclusion) and open settlement panels at each site along this gradient, this experiment examines the role of temperature and productivity on top-down control by consumers. Here, researchers are extending the duration of this work to utilize the current El Niño as a natural experiment to measure how this extreme event will alter consumer interactions on TEP reefs. The El Niño event forecasted for 2023-2024 (NOAA 2023) is predicted to (a) cause extreme increases in water temperature and (b) alter the intensity and duration of upwelling events. Using two complementary experiments to sequentially test the strength of consumer interactions, (a) 4-month predator exclusions and (b) short-term predator exposure experiments, the project tests the hypothesis that increased temperature and decreased upwelling activity linked to El Niño will increase consumer effects in the TEP. Repeating previous experiments during the current El Niño, provides a comparison for how changing temperature and productivity regimes influence consumer effects on the reef communities. By focusing these experiments in a thermally dynamic region of the tropics, this research directly tests for temperature regulation of top-down processes without the confounds of latitude, while also examining the bottom-up consequences of declining productivity due to weakened upwelling activity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.