| Summary: | Corals are sessile animals that are subject to their environment and have various colony morphologies that influence their diffusive boundary layer, a thin layer of fluid surrounding the coral surface. Boundary layer dynamics are crucial for corals to acquire nutrients from the environment, supporting essential functions like calcification. However, we lack knowledge regarding individual and species-specific responses to changes in water column conditions and how these changes can affect boundary layer dynamics and, consequently, calcification. Therefore, the purpose of this study is to incorporate engineering concepts to investigate drivers and connections between the physical and chemical controls on coral calcification in current and future predicted ocean acidification (OA) conditions. The Hawaiian rice coral, Montipora capitata, is a polymorphic coral with multiple growth forms, including branching, plating, and encrusting. Six branching and plating M. capitata colonies were collected, and three of each morphology were exposed to two different water chemistry conditions for two weeks. Microsensor profiles were conducted to measure boundary layer thickness and water chemistry changes, and a flume was designed and constructed to control water flow. The findings show that the plating morphology has a thicker boundary layer than the branching morphology at the site of primary photosynthesis. Moreover, at the site of primary photosynthesis, a significant difference in surface oxygen (O2) concentrations was observed between the two morphologies in ambient conditions, implying increased O2 efflux rates and coral productivity from a branching morphology. Life Sciences College of Science
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