Fire coral (sting hazard)

Fire coral is a colonial organism that looks like hard coral but is actually a hydrozoan. It produces nematocysts that release toxins upon contact with your skin. You will find these colonies in shallow reefs across Koh Tao and Cebu. They often grow in large, branching structures between 2 m and 15 m deep.

Watch your buoyancy carefully. I once saw a diver in Komodo hit a patch while trying to film a nudibranch. The sting felt like a hot needle because the toxins cause immediate inflammation. Do not try to rub the area with sand to soothe it. This mistake makes the pain worse by pushing more stinging cells into your skin. Use vinegar if available to neutralize the sting immediately after the dive.