2010 Volume 5 Issue 4 Pages 156-164
Chronic outbreaks of the coral eating crown-of-thorns starfish (Acanthaster planci) have devastated coral communities throughout the Ryukyu Islands in the past four decades. Since A. planci has high fecundity and long larval duration, knowledge of reproductive timing and larval dispersal are keys to understanding mechanisms of successive recruitment and consequent outbreaks of adults. As the first step to acquiring this knowledge, we monitored water temperature and peak spawning periods using gonad observation. A total of 379 A. planci specimens were collected from May to September in 2004 at five latitudinally different locales in the Ryukyu Islands. Peak spawning, at which starfish gonads rapidly shrunk in size, was first observed in late May in Ishigaki Island, the southernmost sampling site. Then spawning time was progressively delayed with increasing latitude, ie. from mid to late June in Miyako Is., late June to mid July in Kerama Is., late July in Okinawa Is. and Amami Ohshima Is. When we started the survey in May, some A. planci had already started spawning, though not at Amami Ohshima. The peak spawning time in every locality coincided with the time when the water temperature exceeded 28°C. Accordingly, we can predict the approximate peak for spawning by monitoring water temperatures throughout the Ryukyu Islands. The information will be useful for: (1) numerical simulations predicting larval dispersal pathways by particle tracking through provision of the input parameter for the timing of larval release, (2) selecting times for larval sampling in the field in empirical early life history studies.
