Ocean Watch

Monday, June 7, 1999

Open ocean jellyfish
glows in the dark

Recently, my husband came home from work with a snapshot of an enormous, lavender jellyfish in about a foot of clear water. On the back of the picture his co-worker had written, "Sandbar, March 26th, 1995."

"Anna found this while wading on the Kaneohe Bay sandbar. She said it was huge -- as big around as this," my husband said, holding his arms in a wide circle. "Could you identify it for her?"

Sure. Except I didn't know what it was. I hung the picture above my computer with the intention of taking it to the Waikiki Aquarium for identification during my next visit there.

But I didn't have to take the photo anywhere. While paging through David Gulko's "Hawaiian Coral Reef Ecology," a frilly, pink jellyfish practically leaped from the page. No doubt about it, his picture matched the one on my desk.

This jellyfish has no common name but does have a scientific name: Pelagia noctiluca.

Usually, remembering a plant or animal's scientific name is hard because it's either Latin, Greek or the name of the person who discovered it. But in this case, when picked apart, these two scientific names are easy to recall and describe the animal perfectly.

This Pelagia noctiluca is from Dave Gulko's
"Hawaiian Coral Reef Ecology."

Pelagia means occurring in the open ocean; nocti means night and luca means light. In other words, this is an offshore jellyfish that glows in the dark.

Pelagia noctiluca is rarely seen in Hawaii. When it does show up here, it's usually after prolonged, strong winds have blown it ashore.

If you ever get lucky enough to find one of these jellyfish, you won't forget it. These are among the most beautiful creatures in the ocean.

The huge bowl-shaped bells, up to 2 feet across, are pink-to-purple with long, frilly undersides up to 7 feet long.

Pelagia noctiluca has four, maneuverable arms about the same length as its eight trailing tentacles. The arms and tentacles all bear stinging cells, which subdue small animals that run into them. Then, the four arms contract to deliver the prey to the mouth, located under the bell at its center.

The top of Pelagia's bell is covered with spots that are actually clumps of stinging cells. One author reports that after touching one of these bells, he felt pain like tiny pinpricks lasting for about 30 seconds. But beware: The tentacles and arms of this jellyfish can pack a much more powerful punch.

Pelagia noctiluca is found in the surface waters of the North Atlantic, the Mediterranean and the North Pacific. Sometimes, people see these creatures from ships at night, when great numbers of these jellyfish cast off a greenish light as they pulse through the water.

During the summer months in Southern California, winds and currents sometimes sweep large numbers of Pelagia noctiluca to shore, causing stings to swimmers.

Since finding these big jellies is a rare event in Hawaii, Anna's picture is a true treasure. It reminds me that every time I enter the ocean, there's a chance I will find something new and wonderful. When that happens, I hope that, like Anna, I have my camera with me and the presence of mind to use it.