Coral reefs are unique marine ecosystems that are currently being threatened by warming ocean temperatures as a result of climate change. As a keystone species, reef-building corals provide habitats for a diverse range of marine organisms, including symbiotic algae that live inside of coral and provide its main food source. Elevated ocean temperatures often result in corals losing their symbiotic algae in an event called coral bleaching that severely declines overall reef health and can even lead to coral mortality. Observing and analyzing individual coral colonies during successive bleaching events allows scientists to observe coral’s particular responses and better prepare for bleaching events in the future.

This project involved scoring images of 40 individual coral colonies on a 5-point scale based on how bleached they appeared over multiple timepoints. Colonies were initially chosen in adjacent pairs of bleached and non-bleached individuals in order to reduce other potential factors affecting coral health. Underwater images were taken of each colony starting in 2015 and continue to be monitored today. The scored images collected before and after abnormally high ocean temperatures in 2015 and 2019 were used to create figures and perform statistical tests in R studio to compare the two bleaching events.

Our results showed that there were significant differences between the bleaching severity and species responses. For instance, the 2019 bleaching event was much less severe than the 2015 event and mostly affected the species Montipora capitata. Further, Porites compressa showed a more resilient response to the bleaching events but also more variation within the bleached and non-bleached groups. These patterns can be used to better predict the health of coral reefs during bleaching events in the future, along with facilitating methods of conservation. The data and figures contribute to a large “living library” of coral bleaching analysis that investigates coral health and recovery following climate stress.