By: Sarah Barker
You may have heard about algae – most likely in the context of its classification as an aquarium nuisance or as giant swaying ropes of kelp in the ocean. However, it is not an understatement to say that they may just be the single most important part of freshwater ecosystems. Algae encompass an incredibly diverse group of photosynthetic plants which may be found in any place where water is present; including but not limited to ponds, streams, marshes, cracks in building facades, storm water drainage, and even growing on animals! Algae can be large and obvious in a creek, branching out and forming great tufts of emerald green or it can be quite secretive and tiny, colonizing stones and silty stream banks with an inconspicuous yellow-brown film. The most impactful of these varied organisms are often the most overlooked (literally) – microalgae. Microalgae are species of algae which are only visible under magnification. They form communities either attached to a substrate like stones or plants (called benthic) or unattached and freely floating in the water column (called pelagic or planktonic).
Microalgae are powerhouses of energy production, nutrient cycling, and water filtration for the entire stream ecosystem. They generate energy through photosynthesis during the day which is transferred up the food chain as they are eaten by insects which are then eaten by birds or fish which may then be eaten by a person! They also capture and break down harmful pollutants both organic like nitrogen or phosphorus, and inorganic like heavy metals or pesticides. Microalgae are also fantastic carbon transformers; they take carbon dioxide from the water and convert it into less harmful carbon molecules which can then be stored inside their cells or used by other creatures. This process captures carbon that might otherwise be added to the atmosphere and instead stores it safely preventing that carbon from contributing to climate change.
There are a few major groups of microalgae that are especially critical in stream habitats: diatoms, green algae, euglenoids, and cyanobacteria. Each of these members have unique adaptations and each form associations with other kinds of microalgae, bacteria, aquatic fungi, and viruses within the water column causing robust communities of microbes to join chemical forces. These communities are called biofilms and almost always require several different kinds of microbes to function effectively. Biofilms are a mini city in their own right, but the microalgae are the energy grid. These remarkable microbes, diatoms in particular, form complex beneficial relationships with their bacterial neighbors to trade molecules and take advantage of every community member’s strengths. Just as a human community may trade eggs for lavender or tools for cloth, microalgae trade dissolved carbon that they are unable to further break down in return for nutrients and minerals that bacteria are able to process for them. This kind of equally beneficial relationship is called mutualism and is a strategy as widespread in nature as the microbes themselves!
Microalgae embody a very valuable lesson – that true strength comes from community and reciprocity. In order to survive they rely upon products supplied by other organisms: chemicals produced by their bacterial neighbors, and carbon dioxide exhaled by animals. However, in exchange they provide essential oxygen, lower the acidity of the water, break down dangerous contaminants, and act as food for countless grazing stream life. Microalgae are also quite resilient to disturbances and recover from floods quickly, often colonizing habitats where other organisms cannot survive and fixing them up into a once again livable home. All of these wonderful traits are possible through relationships, showing once more how real power lies in connection. Essential support can arrive from even the most unexpected and undervalued places, even scum covered streambeds. When times are rough and the number of trials outweighs the number of celebrations, remember the microalgae filtering polluted water; performing a difficult job that nobody else wants to do for the benefit of all other life downstream. None of us are truly alone – we stand on the shoulders of giants and microbes alike!
Funding for this project was awarded through the “Protect Your Drinking Water” grant program, administered by the Pennsylvania Environmental Council with funding from Aqua, an Essential Utilities company.
References:
Peterson, C. G., Daley, A. D., Pechauer, S. M., Kalscheur, K. N., Sullivan, M. J., Kufta, S. L., Rojas, M., Gray, K. A., & Kelly, J. J. (2011). Development of associations between microalgae and denitrifying bacteria in streams of contrasting anthropogenic influence.
FEMS Microbiology Ecology, 77(3), 477–492.
https://doi.org/10.1111/j.1574-6941.2011.01131.x
Stevenson, R. J., Bothwell, M. L., & Lowe, R. L. (2008). Algal ecology: Freshwater benthic ecosystems. Academic Press.
Yao, S., Lyu, S., An, Y., Lu, J., Gjermansen, C., & Schramm, A. (2018). Microalgae-bacteria symbiosis in microalgal growth and biofuel production: A Review. Journal of Applied Microbiology, 126(2), 359–368. https://doi.org/10.1111/jam.14095
