As a continuation of our previous blog post all about the wonderful world of microalgae, this piece will provide a more in-depth profile on the most important member of freshwater algal communities, diatoms. If you have not had a chance to read the first part of this series, it may be helpful in providing background information and context for this post.
It takes a whole lot of energy to satisfy all the wildlife in aquatic and marine ecosystems. While the most well known photosynthesizers may be terrestrial plants like trees and shrubs, some of the most significant and unusual primary producers on the planet are thriving in local creeks! These underrepresented microbes are called diatoms, a kind of photosynthetic microscopic algae.
When it comes to photosynthesis diatoms are the heavy-weight aquatic champions! Whether they are floating blissfully through the Pacific Ocean, stuck to the leaf of a cattail within a wetland or covering large rocks on the bottom of a riverbed, diatoms are the most proficient primary producers in our waters. They provide between 20-40% of the oxygen available on earth and are the most important member of the base of the freshwater food chain, making up the vast majority of plant matter for grazing animals to feed on from zooplankton to large fish.
Diatoms occupy a very unique position among microalgae, they are the most recently evolved group of algae and therefore, benefit from specialized traits that are not present in other taxa. Diatoms, like all microalgae, are incredibly sensitive to shifts in water chemistry or weather events. However, they have evolved tough cell walls made out of silica (the same material used to make glass) called frustules. This adaptation makes diatoms much more physically resilient than their neighbors and allows them to literally “weather the storm” while other algal cells comprised of cellulose and pectin may be destroyed; this also makes them better armored against infection and predation.
In addition, diatoms employ several different strategies for movement and reproduction depending on the species – as a rule of thumb more diversity within a group provides a greater likelihood of someone succeeding even if it isn’t the whole community. If one strategy fails, another may be more environmentally advantageous; in nature it often pays off to hedge your bets.
Depending on just how recently a species of diatom has evolved, there are several different life paths they can take. The most ancient or ancestral species are planktonic, meaning they cannot move independently of the water’s current. The most newly evolved species (called novel or derived species) can permanently attach themselves to a surface using an excreted glue-like mucus and/or use one or two specialized openings in their frustule called raphes to propel themselves through the water.
Another strange superpower of diatoms is their ability to “hibernate” for prolonged periods of time while buried in sediment. If environmental conditions become unbearable, or high flow blasts diatoms off of their substrate they can simply settle into the stream bed where they become inactive until another forceful current comes along to disturb them from their slumber or conditions become more favorable. This ability is moreso an adaptation as a consequence of their silica cell walls, as they are quite heavy and can cause the entire cell to sink.
In a very vampiric twist, some diatoms can remain inactive in this dormant state for as long as 7,000 years while still being able to resume function according to one 2025 study (Bolius et al., 2025). Diatom reproductive strategy only adds to the immortality rumors – they almost exclusively reproduce asexually, but because of the rigid silica of their cell walls each daughter cell is smaller than the parent. Therefore, the older the diatom, the smaller the cell. Each daughter receives one half of their frustule from the parent and grows one half itself, leaving the parent to grow another half as well, with each resulting cell being both genetically and physically identical.
These tiny plants are generous and full of fascinating mysteries, the depths of which we are only now starting to unearth. Thanks to all their eclectic adaptations diatoms have certainly earned MVP status for habitats worldwide!
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:
Behrenfeld, M. J., Halsey, K. H., Boss, E., Karp‐Boss, L., Milligan, A. J., & Peers, G. (2021).
Thoughts on the evolution and ecological niche of diatoms. Ecological Monographs,
91(3). https://doi.org/10.1002/ecm.1457
Bolius, S., Schmidt, A., Kaiser, J., Arz, H. W., Dellwig, O., Karsten, U., Epp, L. S., & Kremp, A.
(2025). Resurrection of a diatom after 7000 years from anoxic Baltic Sea Sediment. The
ISME Journal, 19(1). https://doi.org/10.1093/ismejo/wrae252
Stevenson, R. J., Bothwell, M. L., & Lowe, R. L. (2008). Algal ecology: Freshwater benthic
ecosystems. Academic Press.
