Secret to stopping jellyfish sting

Richard Collins on how the clownfish holds the key to a new anti-sting lotion.

The seas around Ireland are at their warmest just now and it’s a good time to bathe. Despite claims to the contrary, the great white shark, of Jaws fame, has not arrived here yet and the Irish swimmer’s most fearful enemy is still the humble jellyfish. Not that this little creature, with its pulsating bell, bears swimmers any ill will; jellyfish sting only in self-defence.

However, if you should blunder into the dangling tentacles of some of the larger species, your refreshing dip may end in tears. But fear not, help may soon be at hand; Dr David Boulware of the University of Minnesota has developed the jellyfish equivalent of sunblock. Apply it to the skin before entering the water and you can swim in peace.

Dr Boulware told RTÉ radio’s Mooney show that about 150 million stinging incidents occur worldwide each year. The problem is most serious in warm waters, particularly those of the Indian and Pacific Oceans. Around 50 people are hospitalised annually in Australia and at least 67 have died from stings in the Indo-Pacific region.

The Atlantic, too, has its share of nasty jellyfish. About 200,000 stings are recorded in Florida and over half a million in the Chesapeake Bay area further north.

A most lethal stinger, the Portuguese man-of-war, can be blown to our shores by prolonged south-westerly winds. Neither this, nor its smaller cousin the by-the-wind-sailor, is a true jellyfish. It’s more like colony of co-operating individuals than a single organism. Some members of the colony specialise in feeding, others engage in defence or digestion.

About half a dozen species of true jellyfish occur around our shores. The commonest is known by its Latin name, Aurelia aurita. This little creature has four violet-blue circles on its transparent bell but does not sting humans. Another violet-blue jellyfish, up to a foot in diameter with a thick bunch of tentacles handing downwards, is a much more tricky customer. This, and its orange-red cousin, the Lion’s mane jellyfish, can deliver a painful sting.

Although fairly common, even in shallow water, both species are conspicuous and easy for swimmers to avoid.

Credit for the discovery of the jellyfish-proof lotion must go to a fish. The clownfish is so called because it chooses an unlikely companion with which to live. Anemones are soft-bodied creatures, anchored to stones or corals, which protect themselves by deploying stinging tentacles rather like those of jellyfish. When a young clownfish approaches an anemone for the first time, it moves very cautiously, touching the tentacles very gently.

Once it gains confidence, the little fish moves in and lives among the waving arms. It does so for its own protection; when chased by a predator, the clownfish dives into the mass of sting-studded arms where its enemy fears to tread.

An anemone may even draw in its tentacles and close up completely with the clownfish safely inside. The arrangement benefits both parties.

The fish cleans the anemone’s appendages, removing detritus and dead tissue. It is also the anemone’s guard-dog. Butterfly fish, which are immune to stings, eat anemones. The clownfish rushes out and drives away any butterfly fish which ventures too close to its host. But how does the clownfish avoid being stung?

Dr Boulware and his team have managed to answer this question. Anemone and jellyfish stingers are tiny poisoned arrows, which are fired into an enemy’s flesh. However, firing at every harmless piece of flotsam and jetsam would be to waste valuable military resources, so an anemone has to avoid doing this.

A fish’s skin is covered in a mucous coating containing a chemical which the anemone detects. The clownfish’s coating lacks the chemical and so mimics the texture of the anemone’s own body surface, keeping it from stinging. Dr Boulware’s cream is based on the chemical properties of the clownfish’s coating. A swimmer covered with the lotion mimics the jellyfish’s self-recognition system and so avoids being stung.

The jellyfish lotion was 85% effective when tested in the laboratory. To assess its performance in the field, 82 swimmers agreed to be guinea-pigs.

Guarding against the placebo effect, the lotion was applied to only one side of each swimmer’s body. A neutral cream was applied to the other side. A swimmer had no way of knowing which side of his, or her, body was protected. The participants then swam for 30 to 45 minutes in the open sea.

Thirteen jellyfish stings were reported. Eleven of these were on the side of the body with the placebo and only two were on the side with the lotion. Dr Boulware’s cream may not provide total protection but it should prevent much unnecessary suffering.