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|	|	|	Flow-Induced Stimulation of Dinoflagellate Bioluminescence     Michael I. Latz Keywords: dinoflagellate, turbulence, flow, boundary layer, dolphin Along with Navy physicist Jim Rohr and computational physicist Said Elghobashi, recent research has attempted to blend physics and biology to reveal new insights into the effect of flow on dinoflagellates, the most common source of surface displays of bioluminescence. We have used bioluminescence as a tool to monitor the essentially instantaneous response of cells to flow, and to visualize boundary layer flow on objects such as spheres, ellipsoids, and live dolphins. We have also combined computational and experimental methods to determine the local values of shear and acceleration at the location in a developing flow field where the cell is actually stimulated. Our results can be summarized: There is a clear response threshold for a population of cells. This occurs in laminar flow. By forcing transition to turbulence in pipe flow, we determined that cells respond according to shear stress and not just flow rate. For above threshold flows, average bioluminescence intensity increases with increasing flow rate primarily because more cells respond (several orders of magnitude change), and secondarily because of increased flash brightness (only 5x change). Based on the computational work, cells respond only when the local values of shear stress are greater than threshold. In a developing flow field, this occurs only when the boundary layer starts to develop at the wall. For above threshold boundary layer conditions, the amount of stimulated bioluminescence is proportional to the thickness of the boundary layer. Therefore an object with a laminar, attached boundary layer will stimulate less bioluminescence than one with a separated or turbulent boundary layer. As a demonstration of this, we have used bioluminescence flow visualization to study the flow field around a moving dolphin. Computational studies of an idealized hydrodynamic representation of a dolphin predict suprathreshold surface shear stress values everywhere on the model. Intensified video imaging of the distribution and intensity of bioluminescence on a dolphin swimming in natural seawater suggest that the flow remains attached over most of the body. The observed pattern of stimulated bioluminescence is consistent with the hypothesis that bioluminescent intensity is directly related to the thickness of the boundary layer. For more information on dinoflagellates and bioluminescence, visit the Scripps Web Page. Submitted: 2-Jan-98 The contents of this page are the sole responsibility of the person named below. Michael I. Latz | Scripps Institution of Oceanography | phone: (619) 534-6579 Marine Biology Research Div., UCSD | Scripps Web Page La Jolla, CA 92093-0202  |
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