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.
Where and when to see one
"Resident" means most dives at that destination encounter them; "seasonal" means reliably present in the listed months; anything else is a bonus, not a plan.
| Destination | Reliability | Months | Notes |
|---|---|---|---|
| Sharm El Sheikh & Ras MohammedEgypt | Resident — seen on most dives | Year-round | |
| North & South Malé AtollsMaldives | Resident — seen on most dives | Year-round | |
| Sipadan & MabulMalaysia | Resident — seen on most dives | Year-round | |
| Kona, HawaiʻiUnited States | Resident — seen on most dives | Year-round | |
| MoalboalPhilippines | Resident — seen on most dives | Year-round | |
| Zanzibar & MnembaTanzania | Resident — seen on most dives | Year-round |
Best month, at a glance
Understanding them
Habitat: Coral reef and reef flat, denning in holes marked by middens of emptied crab shells.
Range: Indo-Pacific and Red Sea, from East Africa to Hawaii and French Polynesia.
Behavior: 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.
Diet: Crabs above all, plus shrimp, mollusks, and small fishes trapped under the flared web.
Size: typically around 0.6 m; documented up to 1.0 m (arm-span; mantle to about 16 cm, large animals several kilograms).
How to behave around one
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.
Conservation
Least Concern and fast-growing, though heavily fished for food across much of its range; healthy reef populations rebound quickly.
Charted sites known for them
Watch
From the official channels
Best Places to Dive with Whale Sharks
Outrageously Tiny Fish
Sink or Swim? with Monét X Change | Monterey Bay Aquarium
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