RAPID: Immediate and Subsequent Effects of Coral Bleaching on Fore Reef Community Metabolism

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Coral reefs are among the most productive marine ecosystems that provide important ecosystem services such as food resources and coastal protection. Coral reefs are constructed primarily by calcified invertebrates (corals), and they create habitat for a large diversity of associated organisms, including many fish species. Corals have a narrow range of temperature tolerance and when temperature exceeds a threshold, they "bleach" releasing their primary producing symbiotic algae. Corals can recover from bleaching but a more frequent outcome is mortality. This has the potential to drastically change of the cycle of organic and inorganic carbon on the reef, however we know little about how these processes are affected. Beginning in April 2019, there was a moderately severe bleaching event on the coral reefs of Moorea, French Polynesia, the site of the only NSF-funded LTER program focused on coral reefs. This project leverages knowledge from the MCR-LTER program and measures how the recent coral bleaching affects both reef primary production and calcification both immediately (after 1 month) and over a year- long period at two depths on the fore reef. These are the first measurements of how coral bleaching affects coral fore reef function. The project trains personnel (postdoc, technician), involve graduate students, and results are disseminated to several educational levels (in both the US and French Polynesia) and to island resource managers in Moorea.This project addresses how a recent coral bleaching event in Moorea, French Polynesia affects coral fore reef function (primary production [NEP], respiration [R], calcification [NEC]) over time at two depths. We know that coral reef composition can be affected greatly by coral bleaching. However, we know little about how coral reef function is affected. This project measures coral reef function at 3 time points following the bleaching at 6 sites around the island and at both 10 and 17-m depths. The investigators use a gradient flux approach that quantifies vertical gradients in scalar quantities combined with measures of vertical diffusivity to calculate rates of flux to and from the benthos. They measure NEP/R from oxygen flux and NEC from pH and total alkalinity (DIC flux). All rates are normalized to photosynthetically active radiation to account for temporal variation in light. The investigators predict that NEP/R will not change or might even increase post-bleaching but that NEC decreases in proportion to coral mortality. Coral reef community structure for the metabolic "footprint" at each site/depth combination is quantified using photo-mosaics.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.