Bags attached under the surface of the water are used to analyse the decomposition of leaves by invertebrates. © Gwendoline David/IGB
Zooplankton plays an important role in the development of algal blooms. This is because some of these tiny animals, which float freely in the water, filter large volumes of water and can therefore eliminate floating algae very efficiently. In sub-project 8 "Ecological functions", the algal filtration rates of zooplankton are being determined at five sampling sites in the Oder and the factors that contribute to limiting or completely preventing algal blooms in the lower reaches of the Oder due to zooplankton feeding are being investigated. One aim of the investigations is to determine the threshold concentration of the algae Prymnesium parvum, which is responsible for the 2022 environmental disaster, above which the filtration activity of the zooplankton is reduced.
In addition, the sub-project is dedicated to another central process that is important for the functionality of river ecosystems: the decomposition of fallen leaves by invertebrates living on the river bed, such as leaf-eating freshwater amphipods and some insect larvae as well as leaf-degrading river fungi. Initial investigations have shown that the colonisation densities of invertebrates on standardised leaf packs were very low. The reason for this could be that the animals were exposed to the algal toxin of Prymnesium parvum during the bloom in the summer of 2022.
