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Jellyfish can be poisonous, but also protect some species
By Hope Babowice | Daily Herald Columnist

Jellyfish have no brain, but its tentacles can send out toxins that allow it to catch a bite to eat.


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Published: 10/29/2008 12:02 AM

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"Why are jellyfish so poisonous?" asked Nicholas Farino, 9, a fourth-grader at W.C. Petty Elementary School in Antioch.

They don't have a sense of smell, taste or hearing; they don't have a brain or bones. Jellyfish aren't even fish.

Jellyfish, also called sea jellies and officially cnidarians, are very primitive. They eat, swim and reproduce. There are thousands of species of jellies.

"Sea jellies have stinging cells called nematocysts," said Kelley Niide, aquarist at the Waikiki Aquarium. Nematocysts are microscopic stinging cells located along the tentacles. "Most jellies use these stinging cells to capture their food. Not all jellies are poisonous even though all of them have nematocysts."

Niide said there's another mechanism some jellies use to grab a bite. "Some jellies secrete a sort of mucus that helps trap small prey such as newly hatched brine shrimp - what we feed our jellies." The aquarium's Goldfein Spottswood Jellyfish Gallery includes moon jellies, mosaic jellies and Atlantic sea nettles.

Here's how a jellyfish captures its dinner. As a fish swims past its tentacles, a chemical in the fish's skin triggers the nematocysts to shoot out darts containing venom. Because a jelly has no brain, it has no idea if the object triggering the dart is predator or prey.

Some jellies are beneficial to other organisms. Spotted jellies are used by algae as a place to live. In exchange for a protected jellyfish home, the algae give off chemicals that nourish the jelly. Still other jellies act as "base" to small fish, protecting them from larger prey within their string of tentacles.

A full moon attracts box jellies to the shores of Oahu, Niide said. To avoid their stinging tentacles, swimmers and surfers avoid the beaches during those times when they might be more likely to get stung. "They can deliver a potent sting, and if a person has an allergy to the venom they may be sent to the hospital," Niide said. Those stings can really hurt, but chances are the stings aren't deadly.

However, the sea wasp, a relative of the box jellyfish, causes havoc on the shores of Australia because its sting can kill. Why is the sting so toxic? This jellyfish puts an instant end to its dinner so the wiggly fish won't tear its 15-foot long tentacles. Since chemicals in skin are the trigger for the deadly darts, swimmers and surfers in Australia prevent stings by covering their skin with pantyhose.

Glow-in-the-dark jellies recently made huge waves among humans. A Nobel Prize in chemistry was awarded to scientists who developed a method that uses the luminescent (glow-in-the-dark) protein in jellies to mark genes.

Check these out

The Fox Lake Public Library suggests these titles on jellies:

• "Jellyfish & Other Sea Creatures," by Oxford Scientific Films

• "Jellies: The Life Of Jellyfish," by Twig C. George

• "Jellyfish," by Elaine Landau

• "Beachcombing: Exploring The Seashore," by Jim Arnosky

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