Poison in the blood

A specimen of Zoanthid of the genus Acrozoanthus.
Image: Gary Cranitch


2 June 2010
The zoanthids studied by Yuka Irei are small, sturdy and look great in your aquarium at home. They could also contain enough poison to kill you.
Yuka, a student at the University of Ryukyus in Okinawa, Japan, is focusing on zoanthids during this CReefs Ningaloo expedition.
Zoanthids, related to corals and sea anemones, are an order of colonial animals found in deep sea environments and fringe habitats, such as intertidal, back reef and other shallow areas over dead corals.
Described as button-like, individual polyps are usually less than three centimetres in diameter and feature two rows of weak tentacles. Zoanthids do not grow skeletons, but some incorporate small pieces of sediment, sand and rock into their tissue, and colonies can form a mat on the ocean floor or on other reef structures. Zoanthids gain energy through a combination of photosynthesis through creating symbiotic relationships with algae, and feeding on plankton.
Perhaps the most striking characteristic of zoanthids is that some of them produce palytoxin, one of the most toxic organic substances in the world. Palytoxin can be absorbed through intact skin, and even in small quantities, can be fatal to humans if it is ingested or enters the blood stream.
For example, it has been reported that a home aquarist was poisoned when he accidentally brushed an open cut on his finger against a Parazoanthus species. He was lucky to recover: his zoanthid was found to contain more than two milligrams of palytoxin per gram, enough to kill 125 grown men.
Yuka adds her own story of a researcher who merely swam near a Palythoa species, and was sent to hospital.
"Some Palythoa species have a very strong toxin," Yuka explains.
"If you were to eat it, you would probably die," she says.
Not all zoanthids create the toxin, however.
"Some colonies have very strong toxicity but other colonies don't. It seems to depend on the environment," Yuka says.
While palytoxin is not yet well understood, chemists are investigating it for medical applications, such as use as an anaesthetic.
Yuka is collecting specimens and establishing the diversity of zoanthids from Ningaloo Reef. When she returns to Japan she will study the phylogeny, assisted by her supervisor, Associate Professor James Reimer, who participated in the CReefs Heron Island expedition in November 2009.
Yuka has collected species of Palythoa and Zoanthus, the genera most commonly found in tropical and sub-tropical waters.
She has also made some exciting discoveries.
"I found this specimen of the genus Acrozoanthus living on a worm tube. They have very long tentacles. I've seen this in Taiwan, but I've never seen it in Okinawa," Yuka says.
"I've also found a specimen of Neozoanthus. We don't have distribution data on this species, but it has been seen before in Australia and Madagascar. It's interesting because we found a very similar specimen in Okinawa, and we want to compare the specimens," Yuka explains.
"I think they are similar, but zoanthids often have a large number of different morphs of the same or similar species, so we are not yet sure," she says.