Outbreaks of the crown-of-thorns sea star (Acanthaster planci) are likely to be strongly associated with drastic changes in larval survival influenced by food availability. However, no quantitative or qualitative data are available on the distribution of A. planci larvae in the field nor on the environmental factors that influence their survivorship. Here we use a DNA barcoding approach to describe the distribution of A. planci larvae in Sekisei Lagoon, Ryukyu Archipelago, Japan after conducting three days of high-intensity sampling. High densities (53.3 individuals/m³) of A. planci larvae were found outside of Yonara Channel, which is the largest reef channel in this lagoon. Surprisingly, most (94%) of the aggregated larvae were advanced-stage brachiolaria. Considering that it takes several days to develop to this stage, this result demonstrates that A. planci larvae were floating for some time and maintaining a high-density population. However, this dense larval cloud disappeared immediately after a typhoon. No spatial correlation was found between larval density and either nutrient or chlorophyll a concentrations, suggesting that A. planci larvae do not necessarily aggregate in nutrient-rich water. These data suggest that some high-density populations of late developmental stage A. planci larvae were produced under a low phytoplankton concentration and could potentially trigger an adult outbreak. Consequently, our data suggest that adult outbreaks may not necessarily be triggered by food availability alone.

世界的なサンゴの白化現象が起こり，気候変動が進行する現在，サンゴのモニタリングの必要性が急務である。しかし，モニタリングの手法は目視によるものが基本で，小さい変動はわからなかった。褐虫藻のモニタリングによりサンゴ健康状態をモニタリングできる可能性のある，青色光域と近赤外光域の二つの画像から求めた「サンゴ用正規化植生指標」（NDCI; Normalized Difference vegetation of Coral Index）（斉藤ら 2008）を用いて，石垣島白保サンゴ礁の礁池において2009-2010年と2011-2012年の2年間サンゴの季節変動と日周変動を数値化した。その結果，サンゴのNDCI値は水温に対しては負の相関を示しながら季節変動していること。サンゴの種類によりその変動幅に違いがあること。高水温ばかりでなく低水温や光量子，流入泥によるストレス等により，季節変動のみならず日周変動も行っている可能性を明らかにした。また，Porites sp.の強い白化と弱い白化の可視化，Favia sp.の台風の後のNDCI値の偏りも計測できた。