Dr Tadd Truscott - From Microscale Transport to Reef Scale Prediction

Title: From Microscale Transport to Reef Scale Prediction: How Flow Shapes Coral Response Abstract: Marine heatwaves are typically characterized by temperature, yet neighboring organisms exposed to nearly identical thermal conditions can experience dramatically different outcomes. During the 2023 Red Sea marine heatwave, we observed neighboring coral colonies that remained apparently healthy while others paled and bleached. These observations raise a deceptively simple question: if the temperature is the same, what determines which coral experiences physiological stress? In this talk, I will explore the hypothesis that part of the answer lies in the microscale physics governing oxygen transport. For sessile organisms such as corals, oxygen availability is determined not only by its concentration in the surrounding seawater, but by the balance between metabolic demand and the rate at which oxygen can be transported to and from the organism. Flow alters diffusive boundary-layer thickness, exchange across the coral surface, and transport through complex branching morphologies. Consequently, oxygen conditions within a coral colony can differ substantially from those measured only centimeters away in the surrounding water. Our in-situ measurements and CFD simulations reveal strongly heterogeneous oxygen environments around and within coral colonies and suggest that reduced flow can amplify oxygen stress during periods of elevated temperature. Finally, I will show how we are extending these ideas from individual colonies to an instrumented reef. By combining distributed measurements of flow, temperature, oxygen, and light with probabilistic models we can reconstruct the evolving three-dimensional physical environment across a reef and ultimately begin forecasting conditions relevant to coral stress and restoration. Together, these results suggest that understanding climate impacts on sessile marine organisms requires bridging scales: from micrometer-scale boundary layers and organismal metabolism to colony-scale hydrodynamics and, ultimately, reef-scale environmental prediction.