Kay Dabler, North Webster, found a cluster of zebra mussels on lake equipment belonging to her and her husband, John. Although the mussels’ resurgence means the water in Webster Lake is clearer, that increased clarity is likely to encourage the overgrowth of aquatic plants next season.

Although the zebra mussel population in Webster Lake has greatly declined since 2009’s peak infestation, recent observations indicate the population is returning.

“Anecdotally, people are saying they’re sticking to their pier posts and sea walls again,” reported Lyn Crighton, executive director of the Tippecanoe Watershed Foundation. “They’re in Tippecanoe too, but right now they’re just babies. It’s not bad.”

Indiana Department of Natural Resources does not regularly survey the zebra mussel population in lakes around the state; however, DNR Aquatic Invasive Species Coordinator Eric Fischer said he’s heard about the latest observations.

“There are some biological reasons why they may be coming back somewhat … we’re just in a natural cycle,” he said. “Given the hard freeze we had last winter, and how long it lasted, what you’re seeing now is probably the result of an optimal conditions having happened a year, year and a half ago. But so far it’s nothing out of the ordinary. Just be diligent in transferring equipment.”

Zebra mussels are a non-native invasive species threatening the native species in lakes and streams. They’re named from the dark stripes found on the shell in a wide variety of colors and variations, even though some mussels may not have stripes at all. It’s about a fingernail-length long and has a lifespan of about four years, which may explain its decline in Webster and Tippecanoe lakes between 2009 and 2013.

Zebra mussels can severely affect native species and clams by interfering with their feeding, growth, movement, respiration and reproduction. They attach to native mussels, clams and slow-moving species such as crayfish and turtles and also to piers, boats, sea walls, rocks and any other solid object in the water.

Species of almost any type show natural fluctuations in populations due to reasons including predation and a buildup of their own waste. According to local biologists John and Kay Dabler, though, it’s most likely local zebra mussels cleared the water of desirable food sources and the population declined due to a lack of food.

It has been observed the often poisonous blue-green algae the mussels will not feed on increases as it has less competition from the desirable green algae. The poisons from the blue-green algae, Kay added, may also contribute to the decline of the zebra mussels. The mussels do create competition with the ecosystem, however, since larval fish and other native species also feed on zooplankton and the algae.

The filter feeding of the zebra mussel causes a related and dramatic increase in water clarity, which lake monitor Dawn Meyer and others have observed this year, according to Crighton. That clarity tends to help the population of aquatic vegetation, including exotic invasive plants like Eurasian milfoil, to increase.

To defend local lakes against unfettered zebra mussel growth without harming other species, lake residents should remove objects such as piers, posts, boat lifts, boats, etc., from the water, scrape the mussels from surfaces and allow them to dry out and die on land. According to Fischer, leaving the items outside and out of the water for the winter season will also kill the organisms, since they don’t tolerate extremely cold temperatures.