Many benthic invertebrates utilize broadcast spawning as a reproductive strategy: to spawn, adult males and females extrude sperm and eggs into the surrounding flow. The resulting fertilization success depends on the physics of stirring and mixing across a range of spatial scales; these scales may span five orders of magnitude. In this talk, we describe the different physics that govern this biological process at each end of the spatial scale range, and we summarize a holistic experimental and numerical modeling approach designed to understand and quantify the effect of these physics on fertilization success. We demonstrate that large- scale structured stirring by unsteady or turbulent flow fields selectively aggregates egg and sperm into localized regions to form local hotspots for fertilization efficacy. We show the effect of small-scale mixing on the deformation of chemoattractant plumes released by eggs, and on the resulting chemotactic response of motile sperm navigating within these complex plumes. Our results suggest that sperm motility and taxis acts as an evolutionary adaptation that takes the place of molecular diffusion in traditional mixing and reaction problems. During the course of this talk, I will highlight the various numerical and experimental approaches that we use to explore this problem.