Jelly fish season

The white cross of the jellyfish distinguished its body against the dark background of Yellowwood Lake in Brown County. The rest of its transparent structure appeared as it slowly glided through the water. As stealthily as it surfaced, it sunk back into the darkness below the boat.\nNo one is quite sure when these elegant creatures arrived in local lakes, but their existence speaks to Indiana's impressive biodiversity and begs the question: Why would an animal so closely associated with marine environments annually show up hundreds of miles away from the nearest ocean? \n"They are here because of the cleanliness of the lake," said Betsy Burhans, a park ranger stationed at the Yellowwood State Forest visitor center in Brown County. Yellowwood has one of the cleanest lakes in the area, Burhans said. \nTo minimize pollution, gas-powered motors are not allowed in Yellowwood Lake, and Burhans bemoaned the sight of a small patch of iridescent film floating on the water's surface.\nAfter little luck spotting the translucent jellyfish, Craspedacusta sowerbii, Burhans pointed out some places off the boat dock where she had seen them in the past. \nJellyfish are most often spotted in August and September when the water is warm enough to allow them to grow. But despite the clarity of the lake and the sunlight penetrating deeper into the water as it rose overhead, there seemed to be little sign of these bulbous creatures.\n"With the cool nights, they might go deeper," she said in an effort to explain the jellyfish's elusiveness. \nBut there might be another reason for the lack of visible jellyfish. \nPeople see the more recognizable medusa stage, or reproductive stage, of the jellyfish life cycle, said Terry Peard, professor of biology at Indiana University of Pennsylvania, who studies freshwater jellyfish. Most of the rest of the year is spent attached to the underside of a log as a polyp, a tiny speck of an animal barely 1 millimeter in height. \nPeard's research shows that these jellyfish are heartier -- and more adaptable -- than their delicate bodies, composed of more than 99 percent water, might suggest. \n"We have collected jellies from bodies of water that run the gamut from pristine to various levels of pollution," he said in an e-mail. \nFor some people, jellyfish conjure up childhood memories of that first painful sting, ingraining the jellyfish's diabolical reputation. Unlike some of their marine cousins, freshwater jellyfish are so small that their stinging cells, called cnidocytes, are unable to penetrate human skin. More often than stinging humans, jellyfish use their stingers to catch a more manageable meal of zooplankton -- microscopic, immature versions of aquatic animals ranging from mollusks and fish to lobsters and sea cucumbers -- and occasionally small fish, Peard said.\n"(Freshwater jellyfish) are zooplankton feeders who encounter their food by chance, so a plentiful and appropriate food source is necessary," Peard said. \nAfter almost giving up hope of a jellyfish sighting at Yellowwood Lake, a marble-like figure emerged. Suspended in the shade of a rowboat, a jellyfish could be seen a couple feet under the surface of the water. With a circumference no larger than a quarter, the translucent jellyfish slowly propelled through the water with a gentle undulating motion. \nThese freshwater jellyfish are more than just a curiosity. They are a biological case-study in how species spread. \nClara Cotten teaches invertebrate zoology at IU and has been collecting and rereleasing the jellyfish from Yellowwood Lake and local quarries to present to her class since 1975. \nCotten said that their origin and spread are a mystery. Theories suggest that the polyps hitch a ride on the legs or in the feathers of birds, spreading the species across regions and around the globe. \nPeard said he has found that jellyfish in the medusa form might migrate from site to site in boats, in bait buckets, by flooding or via underground aquifers connecting bodies of water. \n"They are not an exotic part of the North American fauna," said Cotten, explaining that their stable presence does not make them an invasive species like the zebra mussel. "They fit right into the community." \nCotten said her students are impressed by their existence in Bloomington.\n"Most people are unaware they can find them as close to home as Indiana," she said.