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.多年来，我们在开曼群岛小开曼岛西侧海域的大型拿骚石斑鱼（Nassau Grouper）产卵集群形成的卵羽流中投放了漂流浮标（drifters）。针对2017年产生的两个同龄产卵群，我们采用搭载于起伏式拖曳载体（undulating towed vehicle）的原位浮游生物成像系统（in situ plankton imaging system），在产卵后最长36小时的时段内，观测了漂流浮标周边单个鱼卵及幼体的三维空间位置。我们依托这些数据估算了三维扩散-死亡模型（3D diffusion-mortality model）的参数，随后对往年漂流浮标轨迹周边的鱼卵与幼体浓度进行预测，以此评估产卵后5天内，种群发生局地滞留及向外扩散至周边岛屿的可能性。分析结果显示，2017年与2011年的产卵当晚均出现了局地滞留现象；2011年作为关键年份，当年形成的大型产卵同龄群后续推动了该种群的恢复。