Continuous recordings of the coral bleaching process on Sesoko Island, Okinawa, Japan, over about 50 days using an underwater camera equipped with a lens wiper

Abstract

The colours of the hermatypic corals Porites sp. and Acropora cytherea at Sesoko Island, Okinawa, Japan, were photographed continuously, from 19 July to 6 September 2016, by an underwater camera equipped with a lens wiper. The average seawater temperature during the study period was 29.9 °C. The daily average seawater temperature (DAST) was >30.0 °C until 23 August 2016, and a maximum value of 31.2 °C was recorded on 2 August 2016. Red, green, and blue (RGB) values of these corals were analysed based on photographs taken at 14:00. The RGB values of Porites sp. were stable throughout the observation period, while those of A. cytherea gradually increased (i.e. moved toward the "white" end of the spectrum) until the beginning of September. The present study demonstrated the usefulness of RGB analysis of photographs taken by an underwater camera equipped with a lens wiper for monitoring coral beaching.

Keywords: Acropora cytherea; Coral bleaching; Okinawa, Japan; Porites sp.; RGB analysis; Underwater camera equipped with a lens wiper.