Hollie Putnam

Coral reproduction and reef resilience
Natural and anthropogenic impacts are increasingly co-occurring with negative consequences for marine systems, specifically coral reefs. Natural predator outbreaks, such as the corallivorous Crown of Thorns Sea stars, can rapidly kill corals. Further, the stress generated by climate and ocean warming is driving coral bleaching, or the breakdown of the coral-dinoflagellate nutritional symbiosis, which can cause coral starvation and mass mortality. The reefs of Mo'orea, French Polynesia, are currently experiencing an outbreak of Crown of Thorns sea stars, with high coral mortality. In conjunction, the current El Niño warming is driving up ocean temperatures, with the potential to exacerbate peak seasonal thermal stress on corals. In particular, Pocillopora spp, which are dominant reef builders in Mo?orea, are being preferentially eaten by Crown of Thorns Sea stars and have historically displayed coral bleaching during the warmest months. In light of the rapid and extensive coral predation on the ecologically dominant Pocillopora spp on the forereef in Mo'orea and compounding El Niño thermal stress, this project examines the role of lagoon reef Pocillopora spp reproduction, recruitment, and temperature tolerance in reef recovery. Importantly, the project provides information on how the dominant Pocillopora spp are contending with the chronic and acute stress of ocean warming and marine heat waves at sensitive early life stages. The results of this project provide a deeper understanding of the legacy of stress on the ecologically, economically, and culturally significant coral reef ecosystem.

Coral response to climate change
Living organisms may acclimate to environmental changes through epigenetic modifications to DNA, which alter the way genetic instructions are interpreted without altering the DNA code itself. While these modifications to organismal phenotype or function can be reversible, some of them may be inherited by offspring, potentially producing multiple, heritable outcomes from a single genome and affecting ecological and evolutionary outcomes. This project uses symbiotic, metabolically complex reef building corals as a model system to test the connections between physiological, epigenetic, and metabolic states, and predict how population and community dynamics are influenced by epigenetically-modulated phenotypes.

Coral Bleaching Mechanisms
Understanding the complex processes that occur inside cells when reef-building corals are exposed to stressful conditions is essential to guiding future conservation efforts and engineering solutions for the survival of coral reefs. This project will focus on the relationship between corals and the microscopic algae living in their tissue, especially the accumulation and exchange of very reactive molecules (known as free-radicals) during periods of stress, which can have damaging effects on cells at high doses. The symbiosis between coral and algae is crucial for coral reef survival. As conditions in Earth?s oceans change, this symbiosis becomes unstable, such that extreme conditions like marine heat waves lead to expulsion of algae from the coral tissue, turning corals white to the naked eye, a condition known as "coral bleaching." Mass coral bleaching events have increased in frequency and severity. However, the mechanism leading to the breakdown of symbiosis (dysbiosis) is still poorly characterized. The accumulation of free-radicals is understood to be a primary driver of dysbiosis. In this project, researchers will first study the cellular response in isolation and symbiosis of both the coral cells and the dinoflagellate algae cells to create a 3D physical biohybrid coral model. The model will be composed of a hard base mimicking the coral skeleton and bioink combined with coral and algae cells mimicking the coral tissue. This model will allow researchers to study the changes inside the cells and the bioink at high resolution under different conditions, including during stress levels associated with bleaching, according to cell type, cell density and tissue architecture. The characterization toolkit will consist of advanced microscopy, gene expression, metabolomics, nanoprobe measurements, material characterization, computational modeling, 3D printing and 3D bioprinting.