Four of the largest bodies of water in North America, the Great Lakes, have been impacted far more by invasive species than was previously estimated, says a new study.
In fact, much of the damage is from a single invasive species, an ever-hungry zooplankton known as the spiny water flea. This flea has loaded up $80 million to $163 million in damage within one inland lake.
The researchers, from University of Wisconsin Madison, say that their findings suggest it is time to recalculate the financial and ecological cost of invasive species. "Our study indicates that previous attempts to put a price tag on invasive species impacts haven't come close to the true cost," noted Jake Walsh, lead author and a Ph.D. candidate at UW.
These new learnings might also provide background for talking about benefits and costs of the shipping industry that goes to the Great Lakes. Tens of millions of dollars enter the Great Lakes economy each year and have done so for decades via ocean-going ships that bring cargo. At the same time, the link between the Atlantic Ocean and these massive inland lakes has brought in upward of 180 non-native species.
This study looked at secondary invasions, or areas to which invasive species moved after being introduced to the Great Lakes. Researchers also calculated benefits derived by humans from natural resources in the lakes.
The researchers looked in particular at Lake Mendota, an inland lake of 15.21 square miles located in Madison, Wis., alongside the UW campus. It supports swimming, fishing, boating and recreation. However, since 2009 the spiny water flea has been invading its waters. The flea is a native of Russian lakes and arrived in cargo ships' ballast water. Via bait buckets and other conveyances, the microscopic creatures moved to other lakes and now consume a native zooplankton, Daphnia pulicaria.
There's at least one problem with this: Daphnia usually eat algae and make clear water in the lake. But now the native microscopic creatures are being eaten by the water flea before they are able to consume the algae.
Agricultural fertilizer containing phosphorus also runs into the lake, bringing about more algae growth. Without daphnia and with the fertilizer, algal blooms spike and water clarity drops.
Now that the invasive zooplankton are in the lake, they cannot be cleared out. But phosphorus can be reduced. The team determined through statistical modeling that a 71 percent drop in phosphorus would allow the water quality to reach the clearer condition it had before either the fleas or the phosphorus invaded. Doing so could cost from $80 million to $163 million dollars.
This "gives us a clearer understanding of the 'true cost' of invasive species," Walsh said. That said, if we factor in the price of not fighting these invasives, he thinks "maybe we have a much bigger budget than we thought we did."
The findings were published in the Proceedings of the National Academy of Sciences.
Follow Catherine Arnold on Twitter at @TreesWhales.
