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Ocean Watch

Susan Scott

Friday, April 18, 2003


Beautiful form of
jellyfish follows function


During my recent stay on Maui, I walked the south-facing beaches each morning at first light.

One day, I found lying in the sand a full-grown box jellyfish. This transparent case of clear gel, about 2 inches wide and 4 inches long, lay glistening in the sun, still pulsing with life.

I crouched over the dying animal, marveling that this quivering, stinging blob on the beach is also one of the most beautiful and graceful animals in the sea. Jellyfish and their relatives are the Dr. Jekylls and Mr. Hydes of the ocean.

Ocean-goers know well the Hyde side of jellyfish, because some bear stinging cells on their tentacles.

These cells evolved to immobilize tiny drifting animals and small fish, which the tentacle-bearer then eats. But when we humans get in the way of a trolling tentacle, we know it. It hurts.

Not all jellyfish sting, however, and only a few present a threat to humans. According to a publication by the Monterey Bay Aquarium, no jellyfish inhabiting the waters of North America's Pacific coast contains toxins that can kill a person.

A rare exception is a jellyfish relative, the Portuguese man-of-war. Three people have died in the United States from these animal stings, all off the southeastern coast. Most of the time though, stings from man-of-wars hurt for a while and then disappear.

Hawaiian waters host some jellyfish not found in North America, such as stinging box jellyfish. But Hawaii's species have never killed a person, either.

Beyond stinging, jellyfish have a bright side. Their forms and lifestyles are brilliant examples of adaptation.

Jellyfish bodies are about 95 percent water, and since they have no skeletons, they use the surrounding water to support their shapes. Yet these liquid sacks get around well and can be formidable predators.

Typical bell-type jellyfish move by contracting a thin layer of muscle tissue within their bells. This expels the water inside and propels the animal forward. When the muscle relaxes, the bell springs back to its resting shape.

These kinds of jellyfish pulse up and down in the water column, stinging and eating any unlucky creatures that get in the way.

It's hard to predict when and where you will find certain types of jellyfish since they drift with the wind, tides and other ocean currents.

Hawaii's box jellyfish, however, are an exception, washing in on the tidal stream that occurs here nine or 10 days after the full moon.

You might think that a body of jelly inside a breakable bag might be a fast car to extinction, but no. This body works.

First, few predators eat jellies because their low calorie content makes them barely worth the effort. And the predators that do eat them, such as sea turtles, have trouble finding the mostly see-through bodies.

Also, a body with no bones or thick muscles requires little nourishment to keep going. Some jellyfish live perfectly well for long periods without food.

Most people are not fond of jellyfish, but there's much to like in them. David Hume, the 18th-century Scottish philosopher, may have been thinking of these odd animals when he wrote: "Let the form of an object be what it may. Light, shade and perspective will always make it beautiful."

My jellyfish on that Maui beach was beautiful.



Marine science writer Susan Scott can be reached at http://www.susanscott.net.

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