Cyclone damage at mesophotic depths on Myrmidon Reef (GBR)

Abstract

The Great Barrier Reef (GBR) supports diverse, extensive mesophotic coral ecosystems (~30–100 m) along the edge of Australia's continental shelf (Bridge et al. 2012). The first exploration of these deepwater reefs was conducted in the early 1980s using a small manned submersible, the Platypus, at Myrmidon Reef (Hopley et al. 2007). On the eastern reef front, a thriving mesophotic coral community was discovered consisting of large, plating corals (Leptoseris, Pachyseris, and Montipora) and extremely high coral cover (Fig. 1a, b). Nearly 30 years later, we revisited the exposed front of Myrmidon Reef (18.2657°S, 147.4016°E) as part of the Catlin Seaview Survey (September 2012). Using a remotely operated vehicle, we surveyed an area of ~500 m2 between 50 and 65 m depth and observed extensive fields of plate-like rubble, overturned corals, and some living, recently broken-off coral fragments (e.g., Pachyseris, Montipora, and Podabacia) (Fig. 1c, d). Given the signs of recent injury, the observed damage was likely caused by severe Tropical Cyclone Yasi, which passed ~100 km north of Myrmidon Reef in early February 2011, and was the only significant storm in this area since Cyclone Larry in 2006. Mesophotic reefs often escape the effects of storm-induced waves, which may play an important role in their persistence over time and highlights their potential as refugia (Bongaerts et al. 2010). Here, we present the first observations of extensive storm damage at mesophotic depths on the Great Barrier Reef, demonstrating that great depths do not necessarily guarantee protection from severe storms. Given that the severity and frequency of cyclones are predicted to increase due to climate change, we need a better understanding of the growth and recovery rates of coral communities in deeper water.