Increasing current velocity has been negatively correlated with fertilization success of marine broadcast-spawners. Seagrass has been shown to effect seawater hydrodynamics, in particular, slowing the movement of water. In this study we aimed to tease apart the relationship between fertilization success in sea urchins in and out of seagrass beds in St. Joseph Bay, Florida.
Flourescein dye diffusion, as a proxy for gamete diffusion, indicated higher rates of diffusion on the outside of seagrass beds. We quantified the proportion of eggs that remain on a female compared to being advected off the female over a two minute interval in and out of grass beds. Most eggs were advected away from females in both habitats, but more so inside of grass beds. We induced sea urchins to spawn in experimental arrays in and out of grass beds and measured fertilization success of eggs released from females and captured in the water column with a plankton pump and also from eggs placed in sperm-permeable containers. Fertilization success of eggs collected via the plankton pump was significantly higher in grass beds. Sperm permeable containers were less sensitive to habitat differences and showed a slight non-significant trend of higher fertilization in grass beds. Seagrasses act as a benthic boundary layer that mitigate gamete diffusion increasing the reproductive success of those that spawn in them.