Spiny Water Fleas, a Cautionary Tale
By: Rebecca Power
My home watershed is Lake Wingra, Yahara Watershed, Dane County, Wisconsin. Sometime right around 2009, the spiny water flea was found in Lake Mendota, a part of the chain of rivers and lakes in the Yahara Watershed. While I am sad about the fact that there is now one more complicating factor in our efforts to maintain our local rivers and lakes for everyone to use and enjoy, I love the spiny water flea invasion story because it elegantly illustrates the importance of systems approach in water resource management and why we should err on the side of conservation.
So what’s the story, you ask?
The spiny water flea is native to the Ponto-Caspian region of Eastern Europe and Western Asia. It hitchhiked to the United States in the ballast water of a transatlantic shipping vessel, invading the Laurentian Great Lakes. It then hopscotched from the Great Lakes to inland lakes in the Midwest and Northeast U.S., including Wisconsin’s Lake Mendota.
For decades, conservationists have been working to reduce the amount of phosphorus entering Lake Mendota and the associated algae blooms. Phosphorus sources are both urban and rural, with the majority of phosphorus coming from agricultural lands. Recent efforts by a diversity of partners have developed a robust plan for meeting water quality standards and an estimate for how much it will cost.
While human efforts to clean up the Yahara Watershed get most of the attention, we have a tiny partner in our efforts – the algae-munching Daphnia. Daphnia eat enough algae to add 2 feet of water clarity (measured by the depth of secchi disk visibility) in Lake Mendota.
However, to hungry spiny water fleas, Daphnia are “like a nice, slow-moving piece of steak,” according to researcher Jake Walsh. Spiny water fleas have decimated Daphnia populations and led to subsequent increases in days where the water in Lake Mendota is green and murky. Walsh and others estimate that a 71% reduction in phosphorus would be required to return the lake to pre-invasion conditions, costing between $80 and $163 million. This is on top of – and substantially more than – the estimated $44 million to meet to water quality standards.
And this is just one lake, in one Midwestern U.S. state.
For me, this story is a reminder of how important a systems approach is to maintaining our soil and water resources. If I want to reduce algae blooms in my home watershed and across the North Central Region, I need to consider ballast water management as well as nutrient management planning. Projects like the STRIPS project led by Iowa State University, or projects that deepen our understanding of the microbiome and its impacts on soil and nutrient cycling remind us to think more broadly about how to be effective stewards of water resources.