Monitoring mesophotic scleractinian corals using an underwater mini-ROV to sample eDNA

Mesophotic coral ecosystems (MCEs) are light-dependent tropical or subtropical communities occurring at depths of 30 to 150 m. We recently devised a coral-specific environmental DNA (eDNA) barcoding method that can identify 36 scleractinian genera in shallow reefs by sampling ~1L of surface seawater. If eDNA barcoding is combined with sampling using underwater mini-Remote Operated Vehicles (mini-ROVs), it may be possible to survey mesophotic corals more easily and broadly. Around the Zamami Islands, in Okinawa, Japan, seawater was collected 1–2 m above the bottom at six locations 20–80 m below the surface and subjected to coral-specific eDNA amplification. Metabarcoding analyses showed that (a) eDNA from ~0.5 L seawater was sufficient to identify genera and to yield comparative ratios of genera at these sites; (b) Acropora dominates shallow reefs and upper ridges of slopes, while other genera including Porites, Pocillopora and Polyphyllia are more abundant at mesophotic sites; (c) one s...