Aquatic mesocosms, or experimental water enclosures, are designed to provide a limited body of water with close to natural conditions, in which environmental factors can be realistically manipulated.

Such mesocosms provide a powerful tool to link between in situ but often only correlative field studies on the one side, and small-scale far from natural laboratory experiments including a single or a few species only, on the other side. Thus mesocosm studies have the advantage compared to laboratory approaches that it maintains a natural community under close to natural conditions, taking into account relevant aspects from ‘the real world’ such as indirect effects, biological compensation and recovery, and ecosystem resilience.

The mesocosm approach is therefore often considered to be the experimental ecosystem closest to the real world, without losing the advantage of reliable reference conditions and replication. By integrating over multiple direct and indirect species effects up or down the food web, the responses obtained from mesocosm studies can be used for parameterization in ecosystem and biogeochemical models.

See a short video about mesocosm experiments.