AUV exploration of the mesophotic reef zone in the South Ryukyu Islands

2017 Fiscal Year Final Research Report

• Project/Area Number: 16K17819
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Geology
• Research Institution: Nagoya University
• Principal Investigator: Humblet Marc 名古屋大学, 環境学研究科, 特任准教授 (40623616)
• Research Collaborator: Maki Toshihiro ; Furushima Yasuo ; Iryu Yasufumi ; Sakamaki Takashi ; Sinniger Frédéric
• Project Period (FY): 2016-04-01 – 2018-03-31
• Keywords: Coral reef / Mesophotic habitats / Benthic communities / Seafloor topography / AUV / ROV / Scleractinian corals / Ryukyu Islands

Outline of Final Research Achievements

The mesophotic seafloor around the Sekisei Lagoon was surveyed at two sites: site KT (lat. 24.27°, long. 124.08°; 30-110 m), site TN (lat. 24.35°, long. 124.08°; 30-45 m), using robotic submersibles. A new autonomous underwater vehicle (AUV HATTORI) was developed to acquire high-resolution video images of the seafloor. The AUV was equipped with sensors measuring temperature, salinity, and light intensity down to 45 m at both sites. Additional video images were acquired using remotely operated vehicles.
There are differences in coral communities occurring at upper mesophotic depths (30-40 m) between site KT and site TN: low coral cover and taxa comprising Porites and merulinids at site KT, and high coral cover with abundant Leptoseris and Acropora at site TN. In addition, a clear depth zonation was observed at site KT with a transition from coralgal communities to a mixed community at around 60 m. This study also highlights the patchiness of benthic communities at mesophotic depths.

Free Research Field

地球科学