TROY, N.Y. -- Scientists at Rensselaer Polytechnic Institute have found that zebra mussel larvae die in water from New York's scenic Lake George.
Researchers at Rensselaer's Darrin Fresh Water Institute (DFWI) suspect that calcium levels in this important New York lake are too low for newborn zebra mussels to mature. Further tests are needed to determine exactly what causes healthy larvae to die within a week when placed in water from the 32-mile "Queen of American Lakes."
Older mussels have no difficulty developing when placed in Lake George water, said DFWI Director Sandra Nierzwicki-Bauer, professor and chair of biology at Rensselaer. But when larvae less than two weeks old are placed in the lake's water they all die within seven days. The young larvae develop at normal rates in water from Lake Champlain, which is already heavily populated by zebra mussels.
The tests were all conducted in the DFWI laboratories on Rensselaer's Troy campus and not at the university's field station at Bolton Landing. "Understandably, we did not conduct these tests in the lake itself. But we did try to mimic lake conditions to the best of our ability so that we could predict what would happen in the lake," Nierzwicki-Bauer said.
Good News for Lake George The recent discovery will come as good news for Lake George residents, tourists, and business people who have followed the five-year zebra mussel research at the DFWI with great interest.
Zebra mussels are not welcome at Lake George since they are a nuisance species. In infested waters, they clog water intake pipes that supply reservoirs and industry. They cling in crusty masses to boat docks and buoys. Their shelled corpses stink on hot sandy beaches. They torture bare feet, drive out tourists, steal food from native mollusks, and disrupt the fragile ecosystem.
But celebrations of the discovery should be tempered by the fact that zebra mussels in more advanced stages of maturity can enter Lake George aboard boats, bait buckets, aquatic birds, and by other means, said Nierzwicki-Bauer. These adults could survive and live five to eight years. Over time, these mature mussels could produce offspring that adapt to the lake's low-calcium conditions, Nierzwicki-Bauer said.
"One of the amazing wonders of the natural world is that creatures can adapt. Nature can produce offspring that survive and prosper where they once would have grown weak and died. So it is always important to exercise caution and not give zebra mussels a foothold," she said.
"But our findings continue to provide hope that Lake George will escape the devastating impact that other lakes have experienced when these menacing mussels take up residency," Nierzwicki-Bauer said.
A zebra mussel pair can produce and fertilize several million eggs a year. "That's the bad news. The good news is that 98 per cent of these die even in the most mussel-friendly waters," Nierzwicki-Bauer said.
Zebra Mussel Larvae Have Been Found in the Lake In previous years, zebra mussel larvae, called veligers, have been found in Lake George by the DFWI's zebra mussel research team that includes Marc Frischer, assistant professor at Skidaway Institute of Oceanography in Savannah, Ga. But no adult zebra mussels have yet been found by the scientists and their graduate and undergraduate students.
"We suspect that the veligers we did find were produced by adult pairs that have entered Lake George. But we have yet to locate them," Nierzwicki-Bauer said. "Nor have we ever found juveniles that had attached themselves to underwater objects and were on their way to becoming adults."
In laboratory tests, the DFWI scientists found that juvenile and adult mussels could thrive and grow in Lake George water, even though that water is lower in calcium and pH than the nearby Hudson River and Lake Champlain where the pesky mollusks are present in great numbers.
Although adult mussels do well in Lake George water, the researchers found that young veligers, ranging in age from one day to two weeks, all died within a week when placed in water taken from Lake George. In water from Lake Champlain the veligers survived and grew at an expected rate.
Low Calcium May Play a Role in Larvae Death Although a headwater for Lake Champlain, Lake George differs significantly from the larger American lake in a number of respects, including the amount of dissolved calcium in its water. The Lake Champlain water used in the DFWI tests contained 20 milligrams of calcium per liter and had a pH of 8.3. The Lake George water contained 12 milligrams of calcium per liter and had a near-neutral pH of 7.5.
The scientists must now see if very young larvae will survive in Lake George water that has had its calcium and pH levels increased. These tests, which will help pinpoint the cause of larvae death and the levels at which larvae would survive, cannot be conducted until next year. "Unfortunately, the last spawning season has passed," said Nierzwicki-Bauer. "We must now wait until May or June when we can gather veligers again."
Scientists know that calcium is an important nutrient for maturing mussels, but they have assumed that a level of 12 milligrams per liter, as found in Lake George, would be adequate. That level does, in fact, appear to be adequate for the development of mussels that have survived the first weeks of life. But it now seems possible that calcium levels must be higher in the very earliest stages of the life cycle, even before the shell begins to form.
For other mollusks in Lake George the calcium levels seem to be quite adequate. Native clams, including a species considered to be threatened in the U.S., thrive in the lake.
The zebra mussel research at Rensselaer is supported by The Fund for Lake George, The Helen V. Froehlich Foundation, and a New York State Sea Grant.
The DFWI research has included the development of a genetic DNA probe to detect microscopic zebra mussel larvae. The DFWI scientists have also concluded a complete survey of all Lake George mollusks. Those findings are now being compiled.
Faculty Contact: Sandra Nierzwicki-Bauer (518) 276-2696