Spring weather brings welcome conditions for flowers and plant life to bloom across the land. The right mixture of temperature, moisture, and light helps keep the green world vibrant. Underwater plant life generally responds to similar environmental encouragements, but a curious discovery in Lake Erie circa 2012 led microbiologists to study an unseasonal display of winter abundance.

The Winter Blooms of Diatoms

Blooms of diatoms—microscopic, photosynthetic algae—were alive and well beneath (and within) the lake’s ice cover. Some of the main winter-spring diatom bloom formers, like Aulacoseira islandica, have a symbiotic relationship with heterotrophic bacteria capable of forming tiny ice crystals, which over time causes the diatom filaments to become buoyant—just as ice cubes float in your favorite beverage. These “diatom ice cubes” float to the Lake Erie ice cover and embed within it, putting them in position to absorb the light needed to perform photosynthesis throughout the winter months.

Environmental Threats

This curious adaptation is threatened by warming global temperatures that have led to widespread ice decline across the Great Lakes, leaving Lake Erie in a nearly ice-free state in several recent winters. This change has left diatoms stuck in murky, light-deprived waters, with their adaptations that benefitted them during winter months suddenly becoming ineffective.

Researchers turned to the shores of Lake Erie to investigate the evolving situation. They sampled the ice-covered (in 2019) and ice-free (in 2020) winter waters of Lake Erie to learn how diatoms were responding to changing environmental conditions. Two main diatom genera dominate the winter blooms: Aulacoseira islandica and Stephanodiscus spp. The abundance of Stephanodiscus spp. was approximately 70 percent lower in the ice-free water column of 2020 compared to the ice-covered water column of 2019. Likewise, the abundance of Aulacoseira islandica was around 50 percent lower in the ice-free water column compared to the ice-covered water column.

With ice cover across the Great Lakes at record lows, researchers expect this trend to continue in future winters. This trend has significant implications for Lake Erie and other lakes across the globe, as diatoms are critically important to regional lake ecosystems and global climate. Changes to the winter-spring diatom communities in Lake Erie and other lakes could result in large-scale biological and biogeochemical change.

In the face of changing environmental conditions, diatoms may be able to adapt by forming clusters with adhesive proteins called fasciclins to “raft” to the surface of muddy waters via “underwater waves” produced by wind, convection, and underwater currents. Additionally, diatoms could increase their use of proton-pumping rhodopins (PPRs)—light harvesting, retinal-containing proteins that could serve as an alternative to classical photosynthesis. Further research is needed to understand how these mechanisms apply to freshwater systems and taxa.

As ecosystems continue to change due to factors such as climate change, understanding the adaptations of key species like diatoms is crucial. By studying how diatoms respond to changing environments, researchers can gain insights into the potential impacts on global biogeochemical cycles and aquatic ecosystems. The findings from studies like those conducted in Lake Erie could provide valuable information for conservation efforts and resource management in the face of a rapidly changing climate.

Earth

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