Invertebrates
Crown-of-Thorns Starfish
Acanthaster planci · Echinoderm — family Acanthasteridae; a coral-eating sea star, often abbreviated COTS
The crown-of-thorns starfish is the reef predator whose appetite makes headlines. A large adult — half a meter of spine-armored arms, often twenty of them — everts its stomach over living coral and digests the tissue straight off the skeleton, leaving stark white feeding scars. At natural densities it is a normal member of Indo-Pacific reefs; in outbreak years populations explode to thousands per reef and can strip kilometers of coral, and repeated outbreak waves rank among the largest single causes of coral loss on the Great Barrier Reef. Divers are often asked to report sightings, and licensed cull teams inject stars on managed reefs — leave removal to them, since a mishandled star is dangerous and crude methods can spread the problem. The spines mean business: punctures bring strong pain, swelling, and occasionally embedded tips.
どこで・いつ見られるか
「常駐（Resident）」とは、そのダイビングスポットでのほとんどのダイブで遭遇できることを意味します。「季節限定（Seasonal）」とは、記載された月に確実に見られることを意味します。それ以外の出会いはボーナスであり、計画の前提にはなりません。
| 目的地 | 信頼性 | 月 | メモ |
|---|---|---|---|
| Cairns & the Ribbon ReefsAustralia | Occasional | 年間を通じて | |
| North & South Malé AtollsMaldives | Occasional | 年間を通じて | |
| Okinawa & the Kerama IslandsJapan | Occasional | 年間を通じて |
ベストな月、一目でわかる
理解を深める
ハビタット: Coral reefs wherever live hard coral grows, sheltering by day and feeding openly during outbreaks.
分布域: Indo-Pacific and Red Sea, from East Africa to the eastern Pacific fringe.
生態・行動: Naturally sparse and mostly nocturnal; in outbreak years densities explode and stars feed in daylight en masse, leaving white feeding scars across whole reef tracts.
食性: Living hard-coral tissue, digested externally by everting the stomach over the colony; a large adult can clear several square meters a month.
サイズ: 目安は 0.3 m; 確認済みの最大記録 0.7 m (total diameter including arms; large adults carry up to about 20 arms).
出会ったときの正しいふるまい方
Report sightings where reef managers ask for them and leave removal to licensed cull teams — improvised chopping can spread damage, and the spines punish bare-handed heroics.
保全
The species itself is not threatened — the management story is protecting coral from outbreaks, whose causes are debated but linked in part to nutrient runoff and loss of predators such as the giant triton.
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