3D in situ imaging of egg and larval dispersal from a Nassau Grouper spawning aggregation off Little Cayman, Cayman Islands

Over multiple years, we released drifters into egg plumes from the large Nassau Grouper spawning aggregation off the west end of Little Cayman, Cayman Islands. For two cohorts spawned in 2017, we used an in situ plankton imaging system mounted to an undulating towed vehicle to observe the 3D positions of individual eggs and larvae around the drifters up to 36 hours after spawning. We used these data to estimate parameters of a 3D diffusion-mortality model and then predicted the concentration of eggs and larvae around previous years’ drifter tracks to evaluate the possibility of retention and export to nearby islands within five days of spawning. These show local retention on spawning nights in 2017 and 2011, a key year when a large cohort was spawned that subsequently drove population recovery.