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Zooplankton eggs break longevity record.

The mud that squished between the toes of vacationers wading in freshwater ponds and lakes in the United States this summer may well have contained a large number of viable eggs from 17th century zooplankton, scientists say.

Researchers have known for many years that some of the many zooplankton eggs laid in lakes and ponds during the spring remain dormant until their environment proves more hospitable--notably, when water levels rise or predatory fish have stopped feeding.

A smaller number of eggs is buried in sediment before hatching and can remain dormant for years. Only when something stirs up their muddy world do they float up close enough to the sunlight to hatch. Indeed, investigators have retrieved from lake sediments viable eggs ranging from 15 to 90 years old.

But Nelson G. Hairston Jr. of Cornell University and his colleagues have now uncovered and hatched two 330-year-old eggs of Diaptomus sanguineus copepods, they report in the September Ecology. The eggs had a median age of 36 to 46 years, and half of them hatched within 7 to 9 months.

The eggs came from a freshwater pond and a lake in South Kingstown, R.I., and scientists determined their age by means of radioactive dating. The pond alone contains roughly 6 billion dormant eggs, they calculate.

"I bet there are eggs that are several centuries old at the bottom of every lake . . . from algae, invertebrates, and crustaceans," Hairston says.

The zooplankton that laid the eggs normally live only 2 or 3 months. But because a drought or other environmental hazard can wipe out an adult zooplankton population, dormant eggs serve as a guarantee that the species will survive through tough times, the authors note.

One of the most polluted lakes in the United States, Lake Onondaga in Syracuse, N.Y., has captured Hairston's attention. He and his colleagues want to find out what organisms exist to help repopulate the lake once it gets cleaned up. So far, the signs appear favorable: Hairston and his colleagues have taken one core of sediment from the lake and found lots of viable eggs, he says.
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Title Annotation:Nelson G. Hairston Jr. and colleagues discovered Diaptomus sanguineus copepods eggs in a freshwater pond that were 330 years old
Publication:Science News
Article Type:Brief Article
Date:Oct 7, 1995
Words:350
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