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Jellyfish Lake: Return from Extinction
Dick Dewey, July 2001
Remember the "big one," the El Nino of 1998? Daily satellite photos tracked a red-colored tongue of warm surface water moving west from Peru to the Philippines, through to India, and beyond. By January of 1998, astounded scientists reported tides half-a-foot higher than normal, ocean temperatures hovering above 95 degrees, cloudless skies, and no trade winds, creating an unbelievable drought that lasted nine months.
Palau resembled autumn in Vermont as the lush tropical forests wilted and died. Palau's reef corals suffered deaths as the coral animals choked from too much oxygen given off by the symbiotic algae living in their tissues. The corals responded by expelling their internal single-celled plants, causing coral bleaching. Then, without the nutrients from the expelled algae, the corals died. And the same warm water, for the same reason, killed all the Mastigias jellyfish in Palau's famous Jellyfish Lake.
Up until last fall, the situation was bizarre, seemingly hopeless, and sad. Palau's reputation as one of the "seven biological wonders of the world" had been based on this magnificent lake and its jellyfish.
One hope remained. Jellyfish have a tiny asexual larval form, called a scyphistoma, that lives attached to the lake bottom. Anemone-like in appearance and about as long as a chocolate sprinkle, if they had somehow survived the warm water, could they perhaps eventually repopulate the lake?
Last November, temperatures in the lake had dropped to a normal 86 degrees. Scyphistoma living in the mud 30 feet deep began producing pinhead-sized jellyfish. They multiplyied by the hundreds of thousands, reaching four million, their former number, by the time of our Zegrahm Expeditions tour last March.
It was as if the jellyfish had never gone. Snorkeling out into the lake's clear water we were surrounded by pristine Rock Island. Below us was a "closed ecosystem," a marine lake that has not recruited any new species for millions of years and receives few new nutrients or minerals. The lake holds microscopic crustaceans, called copepods, in the plankton. It is the copepods that the scyphistoma larvae fed on for almost two years, waiting for the water to cool.
The Mastigias jellyfish were everywhere around us, bumping gently into snorkelers, pulsating, seemingly directionless. One Zegrahm participant described her snorkel with them as "embryonic." Others said it was the most exciting thing they had ever done. Not aimless, Mastigias actually follow the sun across the lake each day, slowly turning counter-clockwise to expose their internal gardens evenly to the hot tropical sun. At night, the jellyfish swim down 40 feet and return to the east end to await dawn. The nightly return is needed for, at the 40-foot level, the jellyfish fertilize their internal plants in the rich chemical soup of the lake.
Jellyfish Lake's jellyfish have returned.
Dick Dewey began guiding Zegrahm tours to Palau and Micronesia five years ago. Dick is a marine ecologist on the faculty on Portland State University. In March 2002, he will be a lecturer on the Clipper Odyssey and will lead the snorkel trip to Jellyfish Lake with Jack Grove.