By
OurAmazingPlanet
updated 6/24/2011 12:52:42 PM ET 2011-06-24T16:52:42

Jellyfish are familiar to many beachgoers who step around them to avoid a nasty sting as they wash up on shore. But on one western Pacific island there's a saltwater lake where divers voluntarily go swimming with the local jellyfish, and one diver caught the experience on video.

Pat Lohmann, an emeritus researcher at the Woods Hole Oceanographic Institution in Massachusetts, was on the tiny island nation of Palau to study the coral reefs surrounding it. The visit to the lake, aptly named Jellyfish Lake, came at the end of the first day of their efforts.

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"Jellyfish Lake was just a fun dive after a full day on the water," Lohmann said.

Migrating jellyfish
Lohmann took an HD camera into the water with him to record the experience and the jellyfish as they swam around.

The main genus of jellyfish in the lake is called Mastigias They are descendents of jellyfish from the ocean that are thought to have ended up in the lake when sea levels were much once higher, extending over the island and filling up the saltwater lake.

Like most jellyfish, Mastigias feed by stinging plankton with their tentacles to disable the tiny animals and capture them. But Mastigias' sting lacks the oomph of other jellyfish species, a good thing for the divers who swim there.

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Lohmann told OurAmazingPlanet the swarm of jellyfish around him did sting him, "but very mild, face and arms, everything else was covered with a wet suit. I've had much worse."

Because their sting doesn't carry the power of other species, Mastigias have also evolved another way of feeding — they have a symbiotic relationship with algae that live in their tissues that use photosynthesis. This process uses sunlight and carbon dioxide to produce carbohydrates that the jellyfish use as fuel.

Because they need to expose their algae helpers to plenty of sunlight, the jellyfish migrate from one side of the lake to the other during the day, moving with the sun.

At night, the jellyfish stop their migration and move up and down in the middle of the lake, avoiding the edges where the sea anemones that prey on them live.

Difficult film set
Lohmann had little chance to observe the swarm of jellyfish around him while he was in the water, as he was too busy making sure his camera was working and getting usable footage. The camera wasn't intended to be used for such an endeavor, and the pouring rain made lighting a big issue.

"There's no viewfinder so I couldn't frame or compose the shots," Lohmann said. "I just tried to get as many different lighting and background combinations as possible."

Still, Lohmann has enjoyed the fruits of his labor.

"I actually got much more from watching the video of the jellyfish afterward at home than I did swimming with them at the time," he said.

But Lohmann has a better idea for filming any possible return trips: "If and when I return, I'll try to shoot in the sun with better optics and in 3-D. 3-D could be very cool."

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