Yes, humans can consume phytoplankton. It is consumed as a supplement. Phytoplankton is a good source of omega 3s, and omega 3s are known to have numerous health benefits to humans.
Phytoplanktons are similar to terrestrial plants in the sense that they can absorb sunlight and produce oxygen through photosynthesis.
For more relevant articles refer to the links given below:
- UPSC Environment and Ecology Questions
- International Union for Conservation of Nature (IUCN)
- UPSC Environment and Ecology