Fall 2021 eNewsletter

Featured Research: Microcystis Buoyancy in Western Lake Erie and Saginaw Bay of Lake Huron

Harmful Algal Bloom churning in the boat wake. Photo Credit: Paul Den Uyl.

Harmful algal blooms (HABs) are an annual nuisance in western Lake Erie and Saginaw Bay, Lake Huron. In these systems, HABs are often composed of cyanobacteria of the genus Microcystis. Microcystis is known to produce the toxin microcystin, which impacts drinking water quality and can result in recreational contact advisories. In addition to toxin production, another unique feature of Microcystis is that it exhibits particularly flexible buoyant vertical migration in the lake water column. This ability allows the genus to exploit gradients in nutrients, light, and consumer abundance that occur with depth in lakes. The ability to move vertically in the water column has important implications for distribution of the potentially toxic bloom, as well as our ability to monitor total HAB biomass from satellites and remote sensing methods.

“In this study, we measured buoyant velocities of Microcystis colonies collected from Lake Erie and Saginaw Bay as a function of light intensity, time of day, and colony size,” says Paul Den Uyl, lead author of this study and CIGLR Aquatic Ecology Research Technician. “We used micro-cinematography, basically a very precise camera setup, to observe colony movement of Microcystis that have been incubated under different light conditions. We then compared and contrasted the results between the two sample locations, which have different nutrient loading concentrations and stoichiometry.”

The main findings from this study include:

    • Microcystis colonies in western Lake Erie were mostly buoyant.
    • Microcystis colonies in Saginaw Bay were mostly sinking.
    • Buoyant and sinking velocities were weakly correlated with colony size.
    • Apparent colony density of small colonies was more variable and responsive to light.

“Understanding the factors that control buoyancy is critical for interpretation of satellite remote sensing data, as well as modeling and forecasting harmful algal blooms within these two systems,” says Den Uyl. “Remote sensing data can only detect surface concentrations of HABs, therefore it is important to understand when Microcystis is on the surface and when it may be distributed to depths that would not be observed through these methods. Ultimately, we aim to better inform current lake models that forecast bloom trajectory, providing better forecasting of HABs distribution. These data will also be used to help develop a model for Saginaw Bay HABs.” 

In addition to the direct implementation into HABs models and forecasting, this study has shed light on the ecology of Microcystis. Previous studies have shown that colony size is a particularly influential determinant of buoyant velocity in natural populations of Microcystis. “An unexpected finding from these experiments is that buoyant velocities were weakly correlated with colony size resulting from a greater plasticity of colony density in small colonies despite the same environmental conditions,” says Den Uyl. “This pattern is likely explained by the observation that smaller colonies tend to be more geometrically compact whereas larger colonies develop more complex shapes that include intercellular spaces.”

Upper left: Sample locations in Saginaw Bay, Lake Huron and western Lake Erie; Upper right: Bottle incubations with lake water at different light intensities (filters are on the bottles); Bottom left: Micro-cinematography setup (a very fancy camera system); Bottom right: A still image produced from the camera (Microcystis colonies are circled in red).

“Studies like this rely on an expert team of scientists to achieve all of the project goals,” says Den Uyl. “The great support provided by Drs. Casey Godwin (CIGLR), Mark Rowe (NOAA GLERL), and Hank Vanderploeg (NOAA GLERL) ensured that this project generated the datasets needed for implementation into HABs forecasting models and within the context of current scientific literature. Dr. Godwin employed the statistical approaches to robustly compare and contrast observations between study site and experimental treatments. Seamus Harrison, a master’s student from the University of Michigan School for Environment and Sustainability, provided significant support in performing sample incubations and collecting observations. We also received support from outside of CIGLR from Dr. Rudi Strickler of the University of Wisconsin – Milwaukee. Dr. Strickler was instrumental in helping setup the micro-cinematography system used for our Microcystis observations.” 

“Much of the research on HABs in the Great Lakes has focused on growth and toxicity in response to nutrients and trophic interactions; it’s nice to expand our focus to an underserved subject that can result in real-world improvements in forecasts,” says Den Uyl.




About the Authors

Paul Den Uyl is a CIGLR Aquatic Ecology Research Technician and much of his work focuses on contemporary microbiological methods, particularly collection, processing, and sequencing of genomic activity of microbial life in the Great Lakes, specifically harmful algal blooms (HABs). He has also spent considerable time investigating the movement and buoyancy of Microcystis sp., a primary member of HABs. Paul received his B.S. in Geological Science with a concentration in Oceanography from the University of Michigan in 2013 where he also continued research on harmful algal blooms (HABs) and the coral disease known as black band disease (BBD). From 2015-2018, Paul worked as a research associate in the DeLong Lab at the University of Hawaii.

Related Articles & Resources

Den Uyl. P.A., S.B. Harrison, C.M. Godwin, M.D. Rowe, J.R. Strickler and H.A.Vanderploeg. 2021. Comparative Analysis of Microcystis Buoyancy in Western Lake Erie and Saginaw Bay of Lake Huron. Harmful Algae. 108. (DOI:1016/j.hal.2021.102102)