COLUMBUS, Ohio -- While studying a recent increase in freshwater sponges in Lake Erie, researchers at Ohio State University found that the sponges were smothering zebra mussels in some areas, eventually killing them.
Researchers first noticed the increase in sponges in 1993 while studying an artificial reef built about 7 years ago near Lorain, Ohio by researchers from Ohio> Sea Grant. It's possible the increase is related to the zebra mussel invasion, which began in the late 1980s, said David Kelch, an associate professor with Ohio State's Extension Sea Grant program.
While the sponges probably will not pose a threat to the entire zebra mussel population, they appear to be lethal to mussels attached to some vertical surfaces, such as the walls in canals and locks, Kelch said.
"Freshwater sponges were here before the zebra mussel, but not in the abundance that we see them now," Kelch said. "While we can't definitively say there is a correlation between the
introduction of the zebra mussel and the increase in freshwater sponges, the timing suggests a relationship."
Changes in water chemistry due to waste by zebra mussels or increases in water clarity, which could also be caused by zebra mussels, may have made the water more hospitable, Kelch said.
The researchers studied the growth of freshwater sponges on the artificial reef in Lorain and on the surface of a shipwreck off Kelly's Island, in Lake Erie's western basin.
Their observations indicated the sponges were only an effective competitor with zebra mussels on the vertical sides of the reef and shipwreck. The sponges were very competitive on these surfaces, jockeying the mussels for the best position to gain access to food.
Researchers also examined 290 sponge-covered mussels attached to surfaces in the Great Lakes-St. Lawrence River system for the study. Of that number, 197 were found dead.
"We found that the effect of sponge overgrowth was only impressive on vertical surfaces, which could be important for control of zebra mussels in some areas, such as in canals or the lock systems," Kelch said. "It would be a long way off, but our research suggests this might be a way to control zebra mussels in those areas."
But, would the freshwater sponge pose as many problems on these surfaces as zebra mussels now cause? Kelch said more research is needed before an answer is known.
The research appeared in a recent issue of the Canadian Journal of Fisheries and Aquatic Sciences. Kelch was a co-author of the paper, along with Fred Snyder, also an associate professor with Ohio> Sea Grant, and Anthony Ricciardi and Henry Reiswig, with McGill University in Montreal.