Increasing awareness of the natives’ value and the potential threats to their survival is a mission of Dr. Dan Marelli, a Florida biologist whose expertise has made him a valued collaborator of the Darrin Fresh Water Institute whenever mollusks enter the picture.
In August 2010, for example, the first Asian clams discovered in the lake were immediately sent to him. He confirmed their identity, and the multi-million dollar effort to eradicate the invasive, or at least to contain its spread, began. When Zebra mussels were discovered in 1999, Marelli was among those who participated in a successful hand-harvesting eradication effort.
Marelli, Janet Klemm and Steve Resler were on Lake George recently, surveying Zebra mussel populations but, for the most part, conducting research on three species of Lake George mussels. According to Marelli, the three species are not distributed evenly or randomly throughout the lake, but, rather, concentrated in separate sections of the lake, and frequently together.
The Darrin Fresh Water Institute Marelli spent several years in the 1990s identifying the locations of the colonies and mapping their contours. Every couple of years since then, Marelli has returned to the lake to check on them.
“We’re conducting a growth and mortality study,” said Marelli. “We tag the shells, return them to the lake and retrieve them when we come back. And then we repeat the process. Some of these mussells are at least sixty years old, if not older.” The research is a long-term project undertaken in collaboration with the Darrin Fresh Water Institute initially funded by the Helen V. Froehlich Foundation, said Dr. Sandra Nierzwicki-Bauer, the director of the Fresh Water Institute.
“When we were first aware of the potential threat of Zebra mussels, we considered the possibility of establishing reserves where the native mussels could be protected. But to do that, we had to know where they were. That’s when we began working with Dan, who’s a scientific diver,” said Nierzwicki-Bauer.
When we visited the lab at Darrin Fresh Water Institute last week, Marelli, Klemm and Ressler were measuring clams that had been tagged in the past. In some, small holes had appeared. They patched them.
“The lab is also the clam hospital,” said Marelli. “We seal the hole and the patch gives the clam a substrate to grow new shell upon, which is what happens. We’ve recovered clams with remains of the patch still on the shell, and still living.”
Marelli likens the clams to oak trees. “An acorn that falls from the oak has only an infintesimal chance of becoming a tree itself. Each larvae has an equally small chance of surviving, maturing and reproducing,” Marelli said .
Nevertheless, the populations have remained stable, and their locations fixed.
“They move around, but never very far. But to keep our samples in place, we placed bricks around the area, creating a pen. They move through the sand, reach the bricks and travel around the bricks,” said Marelli.
Occasionally, a new colony may be established when a feeding perch is lured to the clam’s brood pouch. As it tries to ingest it, the larvae become attached to its gills or fins, where they remain until they develop shells and drop to the lake bed,
Once their shells are formed, the mollusks bury themselves in the sand, where, according to Marelli, “they expend energy pumping water. That’s what they do for a living: pump water.”
But that’s among the ways they benefit the lake’s water quality, said Marelli.
“They recycle the water, remove phytoplankton and bacteria from the water column and sequester calcium,” he said. And as they release waste, they fertilize the plants rooted in the lake bed. “They create a community,” Marelli said.
“They’re biomonitors,” Marelli said . “Because they remain in one area, they can be used as a proxy for whatever pollutants the site has been exposed to. “
According to Nierzwicki-Bauer, the Darrin Fresh Water Institute has received a grant from the Froehlich Foundation to test the native mussels for mercury.
Mussels of varying sizes and ages were collected by Marelli, Resler and Klemm.
“They were shucked and frozen, and they’ll be tested by us this fall,” said Nierzwicki-Bauer.
Thus far, the Zebra mussel and the Asian clam have posed no threat to the survival of the three native species.
A potential threat is from development on land, which can release soils and sediments into the water, destroying the mollusks’ habitat.
Urban runoff can also stimulate the growth of algae, which also poses a threat.
A boat’s anchor being dragged across the lake bottom could also damage the mollusks’ habitat.
“In the best of all possible worlds, we would have moorings where the populations are concentrated, so that danger would be mitigated,” said Marelli.