Protozoa are microscopic single-celled organisms that can be found in water droplets in the compost heap.
They are larger than bacteria and more complex in their activities. Their size varies from 5 to 1000 micrometers.
There are thought to be many thousands of types of Protozoa, and only a few hundred have been identified. These include amoeba and vampire protozoa.
In the compost heap, they act as both primary (first level) and secondary (second level) consumers. That means they both consume organic material and eat bacteria and fungi. Larger protozoa also consume smaller ones.
Bacteria and fungi immobilize some carbon and nutrients. Protozoa can release nutrients such as nitrogen as part of the waste they produce.
They are also a major source of food for earthworms.
Although they play a role in composting, they are generally considered relatively unimportant in the process. They are common in soil, where they play an important part in keeping bacteria in check.
Header image via Wiki Commons.