Mesocosm experiment

Climate change and biological invasions are leading drivers of biodiversity loss in freshwater ecosystems. Extreme climatic events, such as heat waves, are predicted to increase in frequency and intensity with climate change, and with this the success of potential biological invaders may increase. Therefore, we decided to conduct a mesocosm experiment to determine the effects of heat waves and invasions on lake biodiversity.

Around this time in April last year, we were just starting to set up the experiment here at Lund University in Sweden. Despite the rapid spread of covid at the time, we were able to organise water from the nearby lake Ringsjön to be collected and pumped into the mesocosm barrels providing the starting community to get the experiment up and running.

Running this experiment has been a pretty interesting adventure so far! The cold temperatures in January and February bought with them a lot of snow and ice, causing the non-heated mesocosms to freeze over, with the ice being an impressive 20 cm thick! Although this posed a challenge for sampling, this little winter wonderland brought up many more questions and will enable us to investigate freeze-over effects.

In March 2021, due to covid restrictions preventing travel, we enlisted the help of our collaborators at the IGB in Berlin, Germany in order to collect plankton to be added to the experiment as potential invaders. Rita, Ben and Thomas spent the morning collecting plankton from the Müggelsee in Berlin. The samples were then shipped, with the bottles arriving in Lund less than 24 hours later. Tons of healthy zooplankton were visible (a lot of copepods!) and were successfully added to the invasion treatment mesocosms (I and HI). Rita, Ben and Thomas – thank you so much for your heroic effort in enabling us to carry out this invasion event!

Plankton (to be added as invaders) collected from the Müggelsee by the team at IGB (Rita Adrien, Ben Kraemer and Thomas Hintze)

We plan to run the experiment for another few months in order to look at the effects of this invasion event, but we are already starting to see some very interesting results! Masters’ student Nischal Devkota will finish his thesis (focusing on the zooplankton community) next month and we also expect to see some eDNA metabarcoding results very soon! We will be back with exciting results!


Romana Salis and Lars-Anders Hansson