Ocean reefs are thriving ecological systems teeming with life. The predators resident in this environment have specific biological adaptations designed to immobilize their prey. While humans do not number among their natural prey these animals can pose a significant danger to the unwary diver. The most dangerous predators have been recorded as causing a number of human deaths.
The Blue Ringed Octopus carries enough poison to kill twenty-six adults and there is no antidote. The poison is located in the saliva and is transferred by a bite that can penetrate a wet-suit. A little larger than a table tennis ball they are usually pale brown. Their blue rings "light up" only as a warning when they feel threatened. They are not aggressive and human deaths have only been recorded as a result of interference with this creature.
A sting by a Box Jelly Fish is lethal unless treated immediately. Anti-venom has been developed by the Australian Commonwealth Serum Laboratories however the sting is so painful shock can set in before the victim reaches shore and drowning can occur. The Box Jelly Fish grows up to 20 centimeters across each side of the box and has tentacles on each corner that can grow to 3 meters long. Stinger nets are used on North-Eastern Australian beaches to exclude these pale blue predators.
A few species of Cone Fish which live in attractively colored shells have a toxin which is specific to vertebrates and lethal to humans. They have harpoon-like teeth which can penetrate clothing and their proboscis extends to enable the tooth to reach every part of the external shell. The toxin can result in respiratory paralysis, and artificial respiration is required to keep a victim alive.
Another dangerous group of ocean reef predators have the toxic potential to kill humans but few or no deaths have been recorded due to these animals.
Only one species of jelly fish has been proven to cause Irukandji syndrome, five others are suspect. The tentacles of C. Barnesi have stinging cells which cause extreme pain in the form of back and headaches and shooting pains in the chest and stomach. There is no anti-venom for the syndrome.
Sting Rays are venomous, though not usually aggressive. The tail has a spine with a venomous barb. The tail operates like a whip when the ray feels threatened and the barb can inflict serious wounds or death if the barb penetrates vital organs.
Lion Fish are striped and have venomous fin spines. It can take several months to recover from a puncture wound and the spines retain venom even after being separated from the fish.
Stone Fish are difficult to detect blending well with the ocean floor they inhabit. Their dorsal spines release a toxin when pushed. Pain and swelling is immediate and temporary paralysis and shock can occur when numerous spines penetrate the skin deeply.
Like Sting Rays, Sea Snakes produce lethal venom but are not normally aggressive. Most people are bitten as a defensive response in which venom is not injected. In the rare cases where venom is injected anti-venom is available and has been effective in saving the lives of the victims.
The final group of dangerous ocean reef predators are not lethal to humans but can inflict serious pain or injury when provoked. Sea Ferns and Anemones, while appearing to be attractive underwater plants, are equipped with thousands of tiny stinging cells. Sea Urchins and the Crown of Thorns Starfish have toxic spines, while Sea Cucumbers and Sea Slugs have a skin mucus that can irritate skin and eyes. Reef Sharks may bite if they feel threatened and the coral reef itself can have razor sharp edges which will inflict deep cuts.
The presence of these dangerous creatures should not deter you from experiencing the beauty of the world's ocean reefs. If you are venturing out to a reef, simply remember, the safest way to enjoy snorkeling or diving on the reef is to look but don't touch.