Death on the Reef

If I asked you to name the most poisonous creatures on earth, you'd probably give me the name of a plant, or possibly a snake. The sushi fans would likely vote for pufferfish, and quite a few other dangerous species would surely make the list.

Not many of you would offer this:

Palythoa coral - this species is called "Poseidon"

Yet if we measure by LD-50 (the median lethal dose, meaning the dose required to kill 50% of a test population within a measured amount of time), the benign-looking corals of biological order Zoantharia put most other toxic creatures to shame. These corals produce a substance known as palytoxin (chemical formula C129H223N3O54)--and the LD-50 for palytoxin poisoning in adult humans is 8 micrograms. By way of reference...that's eight millionths of a gram--and toxic zoanthids can produce up to 3 milligrams of toxin per polyp.  And each individual "head" is a polyp....

You put me in here with WHAT???

Order Zoantharia consists largely of colonial, tentacled polyp corals, including some of the most common, and most beloved, soft coral species--

the zoanthids: 

See the pretty green corals? They want to kill you.

and the palythoas:

(The blue ones in the center and at the top are palythoas)

You can buy them at any aquarium store that sells soft corals, anywhere in the world. People love their brilliant colors, and because they look like flowers, but these are animals, not plants--and some of them can kill.

Not all species in the order contain or produce palytoxins, and not all of the ones that do excrete it in large enough quantities to render an entire aquarium toxic. Palytoxin isn't absorbed through the skin, which means it has to enter the bloodstream directly--usually via the victim's eyes or an open cut. However, it can aerosolize in the presence of water vapor, and poison a victim through inhalation (which has happened when reef enthusiasts attempt to sterilize rocks by boiling or application of steam).

Scientists officially "discovered" palytoxin in 1971 (ironically, the same year I was "discovered"...) but Hawaiians had known about the toxin for hundreds of years and even used it to poison spears and arrows. They harvested the toxin from a coral they called "limu-make-o-hana" -- "the Seaweed of Death from Hana." 

Not the seaweed of death. This is my abalone, Oscar, above a large colony of blue palythoas.

Many of the Hawaiian zoanthids and palythoas (both of which fall within order Zoantharia)  do contain palytoxin, as do similar corals from other parts of the world. Normally, the corals keep the toxin in their bodies and excrete it in response to threats. Unfortunately, the very act of splitting off polyps (the flower-like heads) or moving them to a new environment is often perceived as a mortal threat, causing the coral to excrete--or spit--a blob of toxic mucus. 

Smart aquarium keepers exercise special caution around these species.

Ironically, the first night I ever blogged about palytoxin I also accidentally handled some new corals with an open paper cut...and ended up with palytoxin poisoning, though I didn't realize what had happened for several hours.

Most likely, these are the ones that got me. Common name: "Fire and Ice"

Symptoms include dizziness, rapid heartbeat, nausea, cramps, diarrhea, lethargy, kidney failure, muscle spasms, cyanosis, and trouble breathing. When the poisoning proves fatal, the cause of death is normally heart failure (heart attack). I got lucky--my symptoms only included the dizziness, nausea, rapid heartbeat and a little trouble breathing. I self-medicated with Benadryl, water consumption, and rest, and recovered completely in about twelve hours.

This colony "walked" away from the larger colony below it. Yes, they're semi-mobile.

One more thing...there is no antidote for palytoxin. Vasodialators can help, but only if injected directly into the heart within moments after exposure. (Anyone seen the movie THE ROCK? Yeah...pretty much that, except that you die of a heart attack...and fortunately, your skins doesn't melt off your body.) In humans, the standard treatment is "supportive care."

Palytoxin poisoning is rare, and seldom fatal--mostly because the majority of popular captive species don't contain the toxin, and the ones that do can "learn" that common handling isn't a serious threat. Also, aquarium water dilutes palytoxin on contact, making it far less likely that reef keepers will receive a toxic dose. That said, best practices in the aquarium world include the use of rubber gloves and glasses when handling dangerous species and not putting open cuts in the water. 

See the green zoanthids in the lower right? They tolerate seahorses hitching to them at suppertime.

You can forget the snake, the scorpion and the pufferfish. That "innocent flower" under the sea will get you faster than all the others put together.