[MARINE_BIOLOGY_INTERNATIONAL] How a venomous cone snail catches and kills fish


LONDON - The BBC has filmed the moment when a venomous cone snail engulfs its prey, spears it with a harpoon-like barb, paralyses it and eats it.

The fish-eating Conus geographus is the most venomous cone snail known.

There are more than 640 different species of the predatory cone snail, or Conus, globally, most of which live in the tropics around coral reefs.

Cone snails are the largest known genus of invertebrates. They eat molluscs, worms or fish, which they catch using "harpoon-like" spears that are loaded with a venomous containing up to 200 different toxins.

Howard Peters, a marine biologist at the University of York in the UK, is studying the global population of cone snails.

He says their venom makes them totally unique.

"Their venom - and the way they deliver it - is the most interesting thing," he explains.

"What they tend to do is bury themselves in the sand and then use their sensors to detect when a sizeable fish comes along.

"They manufacture and store little hollow harpoons in a sac in their body, and they have another sac which synthesises venom."

When the snails sense a worm, mollusc or fish approaching, they "load" their harpoons into their proboscis, and arm them with venom. This poisonous mixture acts as a neurotoxin; it affects the prey's nervous system.

"[They] dart the fish, which it is left paralysed and then eaten," says Mr Peters.

Fish-eating cone snails like the Conus geographus only use a harpoon once. They swallow it while digesting their prey.

Conus geographus was filmed for the BBC Two programme Great Barrier Reef in an aquarium at the James Cook University in Cairns, Australia.

On average, each species has 100 toxins - meaning there are about 50,000 different toxins across all species of cone snail, with very little replication.

Their nerve-blocking chemical cocktails have triggered a great deal of interest in the cone snail in the field of biomedical research.

Cone snail toxins, Mr Peters says, have been studied and developed in to a painkiller for cancer sufferers, which has similar properties to morphine.

These biologically active molecules - known as peptides - have also become the focus of research for drugs to treat epilepsy, Alzheimer's, and Parkinson's.

While cone snails are not being over-fished for research, Mr Peters warns: "If a species goes extinct, you lose the potential to use those toxins forever."

He has been studying cone snail populations around the world to establish which species are vulnerable or already under threat, and is providing the International Union for Conservation of Nature (IUCN) Red List of Threatened Species database with information.

"We have to research every species, its abundance, its distributions, conservation measures, and [the] trade in them," he says.

The 120 or so species of cone snails on the Great Barrier Reef are among the best protected anywhere, with 90 different species found around Australia generally.

The species around the coral triangle and the south Pacific are widely distributed in a number of areas including Papua New Guinea and the Philippines.

While they are mostly found in shallow water up to 20m, there are a number of deep-water species that can live as deep as 500m.

But it is hard to know the status of deep water species as no-one knows where they are, and smaller species in specific locations could face uncertainty in the future, says Mr Peters.

"Occasionally you'll find a species which is highly restricted - that lives in a single bay of a single seamount (undersea mountain)," he says.

"They are more likely to become threatened due to habitat loss."

The biggest dangers to cone snails are thought to be pollution, destruction of habitats and dredging.

Mr Peters adds that it is important to protect the the snails in order to avoid an imbalance in the food chain.

But there is also an international trade in cone snail shells; rare specimens can fetch up to US$5,000.

"Shell collecting seems an innocent pastime but it is one area that can have a high impact," says Mr Peters.

"The trade in cone snail shells is mostly fairly low-cost; [but] it's a bit like postage stamps.

"Professional collectors look for rarity, size and quality, which makes [a shell] more valuable.

Left-handed cone snail shells, meaning they grow by coiling around to the left - something that is much less common than a right-handed shell - also increases the value."

Conus geographus is thought to have caused at least 30 human deaths; a person has about a 30% chance of surviving if stung, according to Mr Peters.

His research, which he is undertaking for his PhD, draws together expert opinion from around the world, and is due to be completed in a year's time.

When it is, it could provide a crucial yardstick against which to measure cone snail populations in the future.


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