Title: "The role of turbulence and structured stirring on fertilization success in broadcast spawners"

Abstract: Many benthic invertebrates utilize broadcast spawning as a reproductive strategy: to spawn, adult males and females extrude sperm and ova into the surrounding flow. The strategy then relies primarily on fluid stirring to bring the gametes together. Locally, the fertilization rate (modeled as a reaction) depends on the co-occurring concentrations of egg and sperm, and these concentration fields are shaped by the structured in the flow field. Many previous studies have demonstrated the effect of stirring and mixing on reaction enhancement for two reactants that initially share a material interface. The broadcast spawning problem suggests a new class of problems where the two scalars are initially separated by a third scalar (the ambient flow) that potentially acts as a barrier to subsequent reactions. Using a combination of analytical, numerical, and experimental approaches, we demonstrate how structured stirring produces selective coalescence of the initially distant gametes, resulting in significant fertilization enhancement. The results have implications for a broad range of problems involving mixing and reaction of initially distant scalars.