Lower mesophotic depths on coral reefs remain poorly studied and little is known about zooxanthellate coral communities at the deepest limit of their bathymetric distributions. Maximum depths have been reported for reef systems including the Bahamas (119 m) and Hawaii (153 m) (reviewed in Kahng et al. 2010). For the world’s largest coral reef ecosystem, the Great Barrier Reef (GBR), it remained unclear to what depth zooxanthellate coral communities extend, although initial surveys indicated that this may be down to at least 100 m depth (Bridge et al. 2012). As part of the “Catlin Seaview Survey”, we surveyed lower mesophotic reefs across East Australia (2012–2013) using a Seabotix ROV (vLBV300). Although zooxanthellate scleractinian corals were often scarce below ∼80 m depth, we encountered Leptoseris communities extending to depths of 125 m (Fig. 1) on the GBR at Day Reef and Yonge Reef (respectively 14°28.46′S, 145°32.34′E and 14°36.96′S, 145°38.22′E), and in the Coral Sea at Bougainville Reef (15°30.17′S, 147°06.15′E). All observed Leptoseris spp. colonies at these depths (∼115–125 m) were small (<10 cm in diameter) and attached to the substrate. Sequencing of the cox1-1-rRNA intron for two of the deepest collected specimens showed a close match (at 99 % identity) with Leptoseris hawaiiensis colonies from Hawaii (Luck et al. 2013). These are the deepest records of zooxanthellate corals for both the GBR Marine Park and the Coral Sea Commonwealth Marine Reserve, and demonstrate that, despite the shallow average depth of the GBR lagoon (∼35 m), light-dependent coral communities extend to great depths on the outer reefs and offshore atolls of Eastern Australia.
Scleractinia (Hard Corals)
Remotely Operated Vehicle (ROV)