MEAD, K. S.: The Mechanisms Of Turbulent Action: How Does Hydrodynamic Shear Stress Affect Fertilization And Development In Sea Urchins?
Marine invertebrates that reproduce by external fertilization release their eggs and sperm into the water column. For animals living in the surf zone, this means that their gametes are exposed to high energy dissipation rates (up to 3000 W/m3) associated with breaking waves. To test the effects of surf zone turbulence, fertilization experiments were carried out in a Couette cell, a device that creates reproducible energy dissipation rates. Gametes from seven species of sea urchins were exposed to energy dissipation rates typical of wave-exposed surf zones. Exposure to high energy dissipation rates during fertilization decreased fertilization and developmental success in several species. The energy dissipation rate created in the Couette cell is affected by both the velocity gradients in the fluid, and the viscosity of the fluid. Some potential mechanisms of turbulent action vary with viscosity, and others are affected by the velocity gradient. To assess which mechanisms of turbulent action might be operating viscosity and velocity gradient were varied separately in a series of Couette cell experiments. A potential mechanism of turbulent action that emerged from this analysis was that surf zone turbulence might affect fertilization success is to interfere with gamete binding. This hypothesis was tested by counting the number of sperm bound to eggs after exposure to energy dissipation rates during fertilization. In addition, the importance of egg size (relative to turbulent eddy size) is discussed for fertilization and development.