Spiny Water Fleas Have Arrived – What Next?

Spiny Water Flea, Bythotrephes longimanus (Credit: Kate Feil via USGS.gov)

On August 25 four individual spiny water fleas were found during routine monitoring of Lake Champlain. The invasive exotic zooplankton species were discovered in the middle portion of the Main Lake between Burlington and Port Kent. Since then they have been confirmed from a total of three monitoring stations. They had previously colonized Lake George and their arrival in Lake Champlain, though disappointing, is not unexpected. Read on to learn more about their potential impacts, the Champlain Canal’s role in the spread of invasive species, and preventative actions needed by all boaters.

Spiny water fleas were first found in North America in 1982 in Lake Ontario. Since then they have spread throughout the Great Lakes and a number of inland water bodies. They reached the Great Sacandaga Lake on the western edge of the Adirondacks by 2008 and Lake George in the Lake Champlain watershed by 2012.

Zooplankton are small animals that live in the water column and drift with the currents. While most zooplankton are microscopic, the spiny waterflea can be seen with the naked eye. Still, a dozen or more would fit on a fingernail. Zooplankton play two very important roles in the ecosystem. First, they provide food for fish, especially rainbow smelt and alewives, the principal prey of lake trout and salmon. Second, they eat algae, potentially keeping some blooms in check.

Dr. Jason Stockwell of the University of Vermont has offered four predictions about how spiny waterfleas could change the ecology of Lake Champlain. Stockwell is the director of the Rubenstein Ecosystem Science Lab on Lake Champlain. Prior to that, he was station chief at the Lake Superior Biological Station in Ashland, Wisconsin. He based his predictions on his own experiences in the Great Lakes and a review of the literature, which mostly compares lakes in the Canadian Shield with spiny waterfleas to those without.

First, he felt that the spiny waterflea’s impacts would most widely be felt in the Main Lake and Mallets Bay. These areas of the lake have clear waters compared to the murkier waters of Missisquoi Bay and the South Lake. Spiny waterfleas use visual cues to find and catch prey, so they would have an easier time feeding in the clearer waters.

Second, spiny waterfleas would compete with rainbow smelt and mysids (a group of small, shrimp-like crustaceans) for food, leading to drops in those two populations. Both rainbow smelt and mysids provide important forage for lake trout and salmon, and both populations have already seen declines. Rainbow smelt were the dominant forage fish in the lake until the arrival and spread of alewives about 2003. While rainbow smelt can eat spiny waterfleas, the large spines provide little nutrition and have been found to fill up fish stomachs without being digested. Mysids, also known as opossum shrimp, play an important role in the energy and food dynamics of the lake. They migrate vertically in the water column each day providing a transfer of nutrients and energy from sediment and deeper water up into the water column.

Third, the prey of rainbow smelt, mysids, and spiny waterfleas are cladocera, another, medium-sized form of zooplankton. Stockwell predicts their population would go down as a result of the new predator. The presence of spiny waterflea affects them in two ways. Most obviously, the cladocera become food. However, the waterfleas also affect the cladocera’s behavior. In the presence of spiny waterflea the cladocera spend less time near the water surface where their food is more plentiful, but so are their predators. As a result, they grow more slowly when spiny waterfleas are present.

Cladocera are a group of medium-sized plankton. While the overall numbers for the group as a whole may go down, some of the species that have behaviors or defense mechanisms that help them avoid spiny waterfleas could actually increase in number.

Fourth, if the cladocera numbers go down, then the things that the cladocera eat may increase. Rotifers are tiny zooplankton. They are too small to attract the attention of spiny waterfleas but constitute the main food for cladocera. Rotifers may just thrive in the presence of the new invasive species.

A fifth possible outcome has been predicted in other systems but not actually measured. Models suggest that spiny waterfleas in a system could lead to a five to ten percent increase in mercury concentrations in fish. Mercury, a potent neurotoxin, accumulates with each step up the food chain, thus smaller organisms have lower concentrations than larger organisms. Spiny waterflea may add another step in a lake’s food chain, thus increasing opportunities for accumulating mercury.

In addition to the potential ecosystem effects that spiny waterflea may cause, they are also a nuisance for anglers. Two-thirds of the length of the animals’ bodies is a long spine that can become caught on fishing line. At very high densities the spiny waterfleas accumulate on the line and make it difficult to reel in.

The potential impacts of spiny waterflea and other invasives like them have led the Lake Champlain Committee and others to call for physical barriers in the Champlain Canal that would limit opportunities for species to spread. Of those exotic species whose origin of introduction to Lake Champlain is known, over 60% entered via canals with the majority of those coming through the Champlain Canal. There are still more waiting to get in. Round goby, a fish species, and Quagga mussels, a close relative of zebra mussels that live in deeper water, are in the Erie Canal system and making their way eastward. The highly invasive plant hydrilla can reach the canal from where it has been found in Seneca Lake. It is not clear how spiny water flea got to Lake Champlain, but it is clear that the Champlain Canal creates the greatest risk of other species getting here. How many more invasive species will Lake Champlain have to endure before the vital link of the Champlain Canal is finally addressed?

Now that spiny water fleas are in Lake Champlain it is ever more imperative for lake users to take steps that will slow their spread to other water bodies. The simple mantra for all gear that touches the lake is CLEAN, DRAIN, DRY. Clean – make sure there are no visible plant or animal parts on your boats or gear. Drain – remove all water from inside boats, coolers or anything else that might have lake water. Dry – don’t reenter water until gear has dried enough to kill anything that might still be living there. This last item is particularly difficult with spiny water flea, since their resting egg stage is resistant to drying. Additional disinfection with bleach or hot water may need to become part of the routine to prevent spiny water flea movement.