Spawning record of hermatypic coral Acropora digitifera documented by the action camera at one-minute interval

Abstract

Recent technological innovations have introduced a new category of inexpensive, compact and shock-proof digital camera called the action camera (AC). An AC manufactured by Casio Computer Co., Ltd., and fitted with a LED ring light specially designed for this camera, was used to record coral spawning in a seawater aquarium during the night. A colony of Acropora digitifera from the reef flat off Sesoko Island, Okinawa, Japan was transferred to a flow-through aquarium located nearby the collection site. The photographing was conducted at 1 min intervals from around 18:00 until LED batteries were exhausted after midnight. The camera with the LED was re-set daily until the spawning was confirmed. The spawning was observed on 5 June 2017, four days before the full moon. The “setting,” appearance of gamete bundles on the colony surface, was first observed near the apical part of the colony around 20:10–20:20 and extended to the lower part around 20:50–21:00. The first bundle particles in the water column were detected at 22:17 and their number peaked to 100 at 22:27. The “setting” in the lower part was still recognized around 22:40. Around 22:50, the bundle particle number in water decreased to <5. Thus, the intensive spawning lasted ≤30 min. The present study shows that an action camera equipped with LED effectively elucidates the details of coral spawning. Considering the stable environment of aquarium tanks, ACs set up in an aquarium located close to the reef will be suitable for remote monitoring of coral reproduction.