PIs: Harvey Bootsma, John Janssen
What is Cladophora?
Cladophora is a branching, green filamentous alga found naturally along the coastline of most of the Great Lakes. Research in the 1960’s and 70’s linked Cladophora blooms to high phosphorus levels in the water, mainly as a result of human activities such as fertilizing lawns, poorly maintained septic systems, inadequate sewage treatment, agricultural runoff and detergents containing phosphorus. Due to tighter restrictions, phosphorus levels declined during the 1970’s and Cladophora blooms were largely absent in the 1980’s and 90’s.
What is the status of Cladophora in Lake Michigan today?
Cladophora washed up on a Wisconsin beach in 2004. |
There has been a recent resurgence of macroalgae, predominantly Cladophora, along the coast of Lake Michigan and other Great Lakes. These algae blooms lead to unsightly and foul-smelling beaches and have negative economic consequences as a result of the lowered beach use. In addition, Cladophora blooms result in reduced quality of drinking water and decreased property values.
Cladophora growing on zebra mussels. |
Reasons for the current resurgence are unknown. Possible causes include increased nutrient inputs, increased water clarity, increased water temperature and changing lake level. While there have been some efforts to remove Cladophora from beaches, ultimately the solution to the Cladophora problem requires the identification of the factors promoting growth in the lake, and if possible the mitigation of those factors.
It is unknown if there are increased nutrient concentrations entering the lake via streams and rivers or if zebra mussels redistribute existing nutrients from the phytoplankton they consume to the Cladophora. Both may be happening. Work on the Milwaukee River indicates that input of the nutrient most likely to foster Cladophora growth, phosphorus, has increased in recent years.
How do zebra mussels contribute to the Cladophora problem?
Prior to the invasion of zebra mussels, Lake Michigan waters were quite turbid, and as a result light did not penetrate deep into the lake. (See the figure below left.) Cladophora, therefore, was limited to shallow water along the shoreline of Lake Michigan. Zebra mussels, now abundant where it is rocky, filter the water, thereby greatly increasing light penetration. This may allow for an increase in the abundance and depth distribution of Cladophora. (See figure below right.)
Rocks on lake bottom in 1986 before zebra mussels. Note absence of algae and the natural cloudiness of the water. |
Rocks on lake bottom in 2001 after zebra mussels. Note algae-covered rocks and increased clarity of the water. |
Waterfowl feeding in Cladophora
on a Wisconsin beach in 2004. |
Cladophora will attach to zebra mussels living on rocks in addition to the rocks themselves. Cladophora is released if something causes the mussels to detach. When large mats of Cladophora wash ashore they carry with them large numbers of zebra mussels and small crustaceans that shelter in the algae. The mussels and crustaceans may contribute to the odor as they decompose and/or become food for waterfowl. The higher concentration of birds results in considerably more fecal material, which contains high concentrations of the bacteria E. coli. In fact, gulls can be the primary cause of high E. coli counts in localized areas.
Crayfish in Cladophora on a Wisconsin beach in 2004. |
E. coli is the EPA recommended indicator for fecal pollution in freshwater. Fecal pollution from humans or animals, including shore birds and waterfowl, can contain disease-causing organisms and presents a potential threat to human health. The waters along the Wisconsin shoreline are monitored for E. coli regularly and any confounding factor, such as fecal pollution from wildlife, only serves to cloud the results and make it difficult to discern serious contamination events such as sewage overflows or agricultural runoff.
Research Areas >>
