Plankton – just drifting along

When you are an aquatic organism, you can live on the surface or at the bottom – or somewhere in between like plankton. Plankton is found in all surface waters. It consists of minute algae and microscopic animals that feed on them.

Planktonic organisms are so small that you cannot see their details with the naked eye. Under a microscope, the world of plankton opens out in front of you: beautiful, often symmetrical algae cells, or transparent and rather odd-looking animal shapes.

Drifting is a way of life for plankton. Phytoplankton floats with currents but does not sink, as algae cells have their ways of staying in the light-filled layer near the surface. While zooplankton also floats, some of these organisms can also swim slowly forward as they look for food or shelter.

The quantity and species of plankton vary with the seasons. In spring the water provides a wealth of nutrients and light, and diatoms and dinoflagellates multiply, often forming mass occurrences. Other algae have their turn in early summer, whereas blue-green algae take over in the middle of the summer. Gas bubbles lift blue-green algae to the water surface in calm weather, which makes them more visible than other planktonic algae.

When a plankton researcher looks at a water sample under the microscope, they can deduce whether the sample was collected in the spring or summer – but also many other things about the water body and its status. Phytoplankton studies are an important part of assessing the ecological status of water bodies.