Green Island Hammerhead Trip (Feb11) C 439.JPG
Green Island - Fire coral (Millepora) sting.
Fire corals are colonial marine organisms that look rather like real coral. However they are technically not corals; they are actually more closely related to jellyfish and other stinging anemones.
Divers often mistake fire coral for seaweed, and accidental contact is common. Upon contact, an intense pain can be felt that can last from two days to two weeks. The very small nematocysts on fire corals contain tentacles that protrude from numerous surface pores.
Unfortunately I got nailed here myself when I was careless taking a picture of a Gorgonian sea fan and didn't see the fire coral or hydrozoan that was right next to it. Still have small scars on my wrist from that encounter. That should teach me to be more careful next time.