Using invasive species to combat native pests might not be the best conservation tool after all. New research from the University of Guelph suggests that harnessing the round goby fish - an invader of Ontario waters - will not help reverse the destruction that zebra mussels have caused for endangered native mollusks in the Great Lakes. 

Native Great Lake mollusks were brought to the brink of extinction following an earlier invasion of the zebra mussel. In theory, introducing the round goby fish - native to the Black and Caspian Sea regions - would drive the intruder away and protect the lake's native mollusks. But in this case, it won't work.

Led by integrative biology professor Joe Ackerman, researchers found that the round goby fish only makes matters worse for native mollusks, which help to clean water used for everything from drinking to fishing and other recreation.

However, zebra mussels, introduced in the late 1980s, have wiped out nearly all of the lake's indigenous mussel species. The researchers say that this is largely due to increased predation, disruption caused to the normal movement and feeding of native species, and increased competition among native fish that are critical to the mussels' life cycle. 

Ackerman said that most native mussels stay in rivers and streams to feed in the Great Lakes. "Mussels need fish for successful reproduction. The larva has to attach to the gills or fins to develop into juveniles," he added.

However, Ackerman wondered whether the round goby fish might help ward off extinction by serving as a new host for mussel larvae. With the help of master's student Maude Tremblay and Todd Morris, a researcher at Fisheries and Oceans Canada, he put his theory to the test.

The researchers compared the development of mussel larvae on round gobies collected from the Grand and Sydenham rivers with larvae on the mollusks' traditional fish hosts. While larvae established themselves on round gobies, only a few successfully developed into juveniles. This suggests that endangered mussels are further threatened by hampered reproduction on round gobies that essentially "wastes" larvae.

"Most invaders prey on native species or out-compete them for food and other resources. Limiting reproduction is a novel strategy for an invasive species," Ackerman said, adding that their findings highlight the need to control invaders in the Great Lakes.

The study was published in the April 6 issue of the journal Royal Society Open Science.