Meeting Abstract
Sessile stony corals rely on their tentacles to absorb essential nutrients from the water around them. For many corals, the tentacles are the only body organ that can move, and the tentacles are known to modify their morphology when the flow or lighting conditions change. Despite the central role of the tentacles, their behavior and the way they function mechanically is poorly understood. Using high speed photography and PIV measurements we recorded the tentacle movement of Dipsastraea favus both in-situ and in a standing wave laboratory flume. Under oscillating flow conditions, we observed that tentacles oscillate with a phase shift with respect to the ambient flow and pressure fields, i.e. the tentacles change their direction prior to the change in the flow. This observation suggested that the tentacles have elastic properties, and raised the hypothesis that these observed properties are a result of an evolutionary adaptation to increase mass transfer rates. To test this hypothesis, we modelled the tentacle as a torsion spring-damper-mass system, used our PIV measurements to calculate the forces exerted on the tentacles, and estimated the spring and damping coefficients as a proxy of the tentacle mechanical properties. This framework will enable us to numerically calculate mass transfer rates of observed and simulated tentacles for a range of mechanical properties. The results will then be used to test the hypothesis and evaluate the potential role of the tentacle mechanical properties and their influence on photosynthesis, prey capture and nutrients supply.
