In an environment like sand dunes, soil stabilization is a great priority for organisms that live there. While much of dune stabilization occurs through plants securing them with roots, there’s a lesser known and almost invisible helper as well.
This little helper goes by many names, such as cryptogamic crust, microbiotic crust, or biological soil crusts. These odd names are nice and all, but what do these actually do and why should we care?
Biological soil crusts are thin layers on top of soil that are a combination of cyanobacteria, mosses, and lichens. Cyanobacteria tend to come first and secrete a sticky substance that binds sand particles together. The cyanobacteria provides the lichen with food, and the lichen helps the small bacteria by regulating moisture and sunlight.
According to a study by Karoline Schulz, not only do soil crusts stabilize soils, they also “increase the content of soil organic matter and the nitrogen concentration through photosynthesis and nitrogen fixation, influence nutrient cycling, modulate hydrological processes, and consequently, influence the establishment and performance of vascular plants.” This makes soil crusts extremely valuable to desert and dune ecosystems where nutrients can be scarce.
Although soil crusts are commonly found as the glue that holds desert ecosystems together, they can be found in coastal California as well. Soil crusts can be seen in Los Osos’ Elfin forest, which is an extremely stabilized dune system with a multitude of native plants including the adorable pygmy oaks. Here, soil crusts are just off the side of the raised plank walkway.
Despite being so important, they are very difficult to see and easy to crush. This is why it is so important to stay on trail in parks that have fragile ecosystems. One wrong step and over a century of biological process can be destroyed. So next time you go out for a hike by the dunes, remember: don’t bust the crust or crush the crypto!
Schulz, K., Mikhailyuk, T., Dreßler, M. et al. Biological Soil Crusts from Coastal Dunes at the Baltic Sea: Cyanobacterial and Algal Biodiversity and Related Soil Properties. Microb Ecol 71, 178–193 (2016). https://doi-org.ezproxy.lib.calpoly.edu/10.1007/s00248-015-0691-7
