It’s just a flea, no bigger than a speck. But it eats like a hog.

That’s a problem because what the invasive spiny water flea from Europe and Asia likes to eat most is one of the coolest and most beneficial life forms in the food chain of Wisconsin’s Lake Mendota, the Daphnia flea. The victim grazes on algae, and the more it eats, the better the lake’s water quality and visibility, making recreational pastimes such as swimming and fishing more pleasurable.

Since their arrival in cargo ships that sucked up fresh water in Europe and the Far East and dumped it in the Great Lakes, spiny fleas have reduced the biomass of Daphina so much that algae growth has spiked, and Lake Mendota’s visibility has clouded, further impairing a resource on which humans and animals rely. Once people could see their toes in water that was chest high as opposed to about thigh high, said the author of a new study that shows how invasive species like the spiny water flea does a lot more damage than people know.

The author, Jake Walsh, a researcher at the Center for Limnology at the University of Wisconsin, said it’s hard to explain just how destructive the flea has been over the past 30 years unless you describe it in a way the average person would understand.

His team used models to estimate the cost of limiting the algae that Daphnia would eat. Algae relies on phosphorous to grow, and much of that runs off cities and farms in sewer waste water and animal excrement, to name just a few things. Reversing algae overgrowth in Lake Mendota would require a 71 percent reduction in its phosphorous pollution. “A phosphorous reduction of this magnitude is estimated to cost between $86.5 million and $163 million,” the study says.

Those estimates “may increase considerably if cases of secondary invasions into inland lakes, such as Lake Mendota, are included. That’s not even the half of it. At least 180 species of invasive animals have been introduced into the Great Lakes by ships that travel across the world. At the root of the problem are humans, who, some argue, are the most destructive invasive species of all in the Americas.

Like numerous other researchers, Walsh’s team blamed phosphorus pollution degrading the quality of lakes and reservoirs, cheapening their aesthetic value, not to mention property values. Algae blooms lead to fish kills that stymie sportsmen and beach closures that hurt swimmers. Blooms can release toxins harmful to humans and fish, and they can suck so much oxygen from water that fish and other animals can’t survive.

Dumping an animal that preys on algae grazers made a bad situation much worse, they said.

Using the spiny flea as an example, the authors emphasized that all invasive species wreak havoc in a way that few have considered. Walsh mentioned the emerald ash borer off the top of his head.

Its march across the Midwest since 2002 has left billions of nickel-sized holes in the ash trees they bore into, killing trees that provide durable wood for home flooring, bowling alleys, church pews, baseball bats and electric guitars. Moreover, they ruin trees adorning sidewalks and front yards, hurting the appeal of cities, not to mention the carbon the trees capture to help improve air quality.

The list goes on. Pythons are marauding across the Everglades. Nutria — a swamp rat — are proliferating in Louisiana and the on Delmarva Peninsula. The Northern snakehead fish is threatening the Chesapeake Bay and rivers in the Mid-Atlantic. Feral hogs are on the march in Texas, Florida and Georgia and are moving into Virginia. And the Asian citrus psyllid has caused “a yellow dragon disease” called huanglongbing that’s killing orange trees in Florida, the source of 80 percent of the nation’s orange juice. That is by no means the entire list; it’s only a few.

The spiny flea, which drags a skinny tail, is about as big as the width of a pinky finger, Walsh said. The paper called it a voracious eater that can consume more microscopic organisms called zooplankton than fish and any other life forms that prey on them combined. Its gluttony alters an entire lake food web, making eutrophication, an explosion of aquatic plant growth made worse by chemicals used by humans.

“Freshwater ecosystems are a cornerstone of human society,” the new study says, used for “drinking water, fisheries, pollution dilution, recreation,” among other things. Policymakers haven’t estimated their true value, “leaving them overlooked and poorly integrated” into the decisions they make on behalf of residents. Decisions, Walsh said, like attempting to eradicate harmful invasive species.

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