Cephalopods
Common Reef (Day) Octopus
Octopus cyanea · Cephalopod mollusk — family Octopodidae; the big day-active octopus of Indo-Pacific reefs, called he'e in Hawaii
This is the octopus most tropical divers actually meet, because it breaks the family rule and hunts by day. A big day octopus flows across the reef as a self-editing special effect — skin texture spiking into algae tufts, color rippling from mottled brown to bone white in under a second, a passing-wave pattern flickering as it moves. Watch a hunt: the animal balloons its web over a coral head and flushes whatever bolts, while jacks or a grouper often shadow it to pick off escapees, one of the reef's neatest hunting partnerships. Dens are readable by the midden of emptied crab shells at the door. Sit still three meters out and curiosity frequently wins, an arm tip arriving to inspect a strobe arm. Let it explore; snatching gear back teaches the animal that divers end hunts.
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 |
|---|---|---|---|
| Sharm El Sheikh & Ras MohammedEgypt | Resident — seen on most dives | 年間を通じて | |
| North & South Malé AtollsMaldives | Resident — seen on most dives | 年間を通じて | |
| Sipadan & MabulMalaysia | Resident — seen on most dives | 年間を通じて | |
| Kona, HawaiʻiUnited States | Resident — seen on most dives | 年間を通じて | |
| MoalboalPhilippines | Resident — seen on most dives | 年間を通じて | |
| Zanzibar & MnembaTanzania | Resident — seen on most dives | 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 reef and reef flat, denning in holes marked by middens of emptied crab shells.
分布域: Indo-Pacific and Red Sea, from East Africa to Hawaii and French Polynesia.
生態・行動: Hunts by day — rare among octopuses — flowing between coral heads and ballooning its web over them; jacks and groupers often shadow the hunt to pick off escapees.
食性: Crabs above all, plus shrimp, mollusks, and small fishes trapped under the flared web.
サイズ: 目安は 0.6 m; 確認済みの最大記録 1.0 m (arm-span; mantle to about 16 cm, large animals several kilograms).
出会ったときの正しいふるまい方
Settle a few meters out and hold still; curiosity often brings an arm tip to you. Never grab, pry at a den, or block the animal's line of retreat.
保全
Least Concern and fast-growing, though heavily fished for food across much of its range; healthy reef populations rebound quickly.
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