Multispecies environmental DNA metabarcoding sheds light on annual coral spawning events

Synchronous multispecific coral spawning generally occurs annually and forms an integral part of the coral life cycle. Apart from spawning times and species participation, however, much else remains unknown. Here, we applied eDNA metabarcoding to study two tropical reef sites of contrasting coral cover before, during, and after, coral spawning. Using coral-ITS2 and vertebrate 12S markers, we evaluated eDNA as an alternative monitoring tool by assessing its capabilities in detecting spawning species and tracking the relative abundances of coral and fish eDNA. Over three years, elevated eDNA coral signals during the event (proportional increase of up to five fold) were observed, detecting a total of 38 coral and 133 fish species with all but one of the coral species visually observed to be spawning. This is also the first demonstration that eDNA metabarcoding can be used to infer the diurnal partitioning of night- and day-time spawning, spawning in coral species overlooked by visual surveys, and the associated changes in fish trophic structures as an indicator of spawning events. Our study paves the way for applied quantitative eDNA metabarcoding approaches to better study ephemeral and ecologically-important events.

多物种同步珊瑚产卵通常每年发生一次，是珊瑚生命周期中不可或缺的核心环节。然而，除产卵时间与参与产卵的物种外，该过程的诸多细节仍未得到充分阐释。本研究采用环境DNA宏条形码（environmental DNA metabarcoding, eDNA metabarcoding）技术，在珊瑚产卵前、产卵期及产卵后三个阶段，对两处珊瑚覆盖度存在差异的热带珊瑚礁点位开展研究。本研究以珊瑚ITS2基因与脊椎动物12S基因为分子标记，通过评估eDNA技术检测产卵物种、追踪珊瑚与鱼类eDNA相对丰度的能力，验证其作为替代监测手段的可行性。历时三年的观测结果显示，产卵期间珊瑚eDNA信号显著升高，相对增幅最高可达5倍；本次研究共检测到38种珊瑚与133种鱼类，其中除1种外，其余所有珊瑚物种均经目视调查确认处于产卵状态。本研究同时首次证明，eDNA宏条形码技术可用于推断夜间与日间产卵的昼夜时间分配模式、识别目视调查遗漏的珊瑚产卵物种，还可将鱼类营养结构的相关变化作为产卵事件的指示指标。本研究为应用定量eDNA宏条形码技术，更深入地研究这类短暂发生且具有重要生态意义的生态学事件铺平了道路。