The plankton organisms tell their story of the state of the water. They react faster to changes in their environment compared to the slower, larger organisms, such as water plants and fish.
Plankton species, various algae groups (blue-green algae, green algae, golden algae etc.) and zooplankton groups (rotifers, cladoceras and copepods indicate the state of the surrounding water. In biology – the science exploring the living nature – the phenomena aren’t as simple as 1 + 1 = 2, the information and its interpretation is much more complicated. But that’s how life is – at organism level too.
Phytoplankton is commonly used for monitoring and analyzing the surface water (lakes, rivers, and sea areas).
Zooplankton is used much less, although it also provides a lot of information that is otherwise difficult to detect.