Hydrilla could threaten marine life in Cayuga Lake

Oct 13, 2011

There’s another invasive species that’s threatening to destroy the habitat of numerous other plants and animals. This one lives underwater. It’s called hydrilla and it’s spreading through the Cayuga Inlet near the south end of Cayuga Lake. Ithaca’s mayor has already declared an environmental emergency and ordered all boat traffic to stop through Cayuga Inlet to try and stop the plant from spreading. 

Cayuga Lake stretches 40 miles from Ithaca all the way north to Seneca Falls. In season, sport fishing for pike, bass and perch abound. The lake is extremely attractive to recreational boaters and hosts 12 marinas and a yacht club. Three lighthouses illuminate the coast. The lake brings in significant tourism dollars to tax revenue to an area mostly known for agriculture. 

But all this fun in the sun faces a new threat: the invasive hydrilla verticillata. The aquatic tapegrass has taken hold in waterbodies on both coasts, often killing native plants and fish. Dr. Holly Menninger is a Cornell professor and member of a task force working to prevent hydrilla from gaining a presence in the lake itself.

"We have found it growing in the inlet to Cayuga Lake," says Menninger. " So just south of Cayuga Lake. Hydrilla is growing pretty densely and in several locations."

Hydrilla is distinguished by five serrated, toothy leaves growing around a stem that easily severs when pulled. It spreads aggressively and officials are concerned that it could rifle through the canal system, into other Finger Lakes and eventually reaching the Great Lakes. Severed stem fragments can drift along the water and take root on new soils. In autumn, the plant produces tiny buds, called turions that detach and act like pine cones floating on the water. They form new hydrilla infestations wherever they land. 

Dave White, a program coordinator with New York Sea Grant says to wreak havoc, the plant first has to reach the water's surface.

"It's a very fast growing plant, and when it reaches the surface, which it can do very quickly, it grows horizontally and develops a mat on top the water. You then have it restricting light flow to the bottom and restricting other plant growth," says White.

Once that dense canopy has formed, Dr. Menninger says it spells disaster for the native species.

"Things like pond weed and wild celery and eel grass will probably disappear," says Menninger. "When you have a huge monoculture, that does not creative a very good habitat for fish or insects that rely on a complex environment under the water." 

Reductions in biodiversity leave migrating waterfowl with fewer food sources. Infestations have also been shown to reduce the weight and size of sport fish, such as salmon and bass. Uncontrolled hydrilla infestations can even reduce dissolved oxygen in the water column leading to fishkills.

The inlet's marina closed early this season to reduce the risk of moving hydrilla into the lake. Ithaca mayor Carolyn Peterson has declared the situation an environmental emergency. The inlet has been closed to prevent hydrilla from spreading any further into the lake and allow for the alppication of aquatic herbicide, which  management efforts in california have shown to be very effective at killing the plant. 

"If it gets into shallow bodies of water-like a canal-like a stream-like a river-it can begin to take--then you have to look at very aggressive management, like mechanical harvesting, or some control through herbicide or others," says New York Sea Grant's Dave White. 

Applying aquatic herbicide has cost upwards of $500 an acre in other lakes. What that number doesn't reflect is time spent getting the necessary permits for herbicide use and concerns about the adding toxic chemicals to the water. Mechanical harvesting can cost more: up to $1,000 an acre. 

"People have to remember that as unpalatable as some of the management options are now, I think we need to fast forward to a couple of years from now: what would happen if we left hydrilla unchecked. I think that would make the waterways unusable and the edges would just be choked with hydrilla," says Cornell's Holly Menninger.

Scientists agree that if hydrilla establishes itself in Cayuga Lake, it will hurt the both the fishers, farmers, boaters and other stakeholders-as well as the native ecology. The only question is by how much.