Mesocosm experiments can reveal how warming and animal communities affect greenhouse gas emissions
Creating controlled mini-ecosystems, called mesocosms, is one way for researchers to study factors that influence processes in the sea. This summer, a large experiment of this kind was conducted at the Askö Laboratory, to investigate how emissions of greenhouse gases from shallow coastal bays are affected by global warming and by animal communities in the water and sediment.
Moritz Nusser, Monica Silva Figueriedo and Maria Valio are collecting water samples during the experiment. Photo: Sara Westerström
In total 25 mesososm were placed in the large containers outside Askö Laboratory. Photo: Sara Westerström
Titouan Trancy and Sara Westerström collecting sediment samples of different depth layers at the end of the experiment to analyse important biogeochemical and microbial parameters along a vertical gradient. Photo: Moritz Nusser
Water from the Askö Bay was pumped through the mesocosms, either untreated or heated 3 degrees. Photo: Sara Westerström
Moritz Nusser is sealing the mesocosm airtight with a special lid. Measurements of greenhouse gases before and after this encubation enables analysis of the fluxes. Photo: Sara Westerström
Understanding the connection between coasts and climate is a key question for researchers in CoastClim. This summer, Sara Westerström and Moritz Nusser from the Research School Perspectives on Climate Change in Coastal Seas took a new approach to investigating how small animals in the water and in the seafloor can affect greenhouse gas emissions, both now and in a warmer future.
Sara Westerström and Moritz Nusser collected the material for the mesocosms around Askö island. Photo: Yvonne Yu Yan Yau
"We're particularly interested in the fluxes of carbon dioxide, methane, and nitrous oxide from shallow bays, and how these are affected by warming and different animal communities," explains Sara Westerström.
To examine this in a controlled way, Sara Westerström and her colleague Moritz Nusser set up an experiment containing a large number of mesocosms – miniature ecosystems in glass containers – created to resemble a typical shallow Baltic Sea bay.
“We collected sediment directly in the mesocosms using a box corer. Then, we planted shoots of Stuckenia pectinata, a common species in shallow bays, in each mesocosm, and added some Cladophora, a common filamentous green alga', explains Moritz Nusser.
Different treatments
Shoots of the plant Stuckenia pectinata and some filamentous green algae were added to mesocosm. Photo: Sara Westerström
In addition, the researchers collected grazing animals (Theodoxus, Gammarus and Idotea) and benthic animals (Macoma and Monoporeia). The grazers were added to one third of the mesocosms, the benthic animals to a further third, and the remaining third remained without animals.
All the 25 mesocosms (including one for control were then connected to a flow-through system that continuously pumped seawater from Askö Bay.
"Half of the mesocosms received water heated by three degrees to simulate future ocean warming, while the others received unheated bay water," says Sara Westerström.
Multiple measurements
The experiment ran for 21 days, dyring which the fluxes of carbon dioxide (CO₂) and methane (CH₄) were measured on several occasions using a Picarro gas concentration analyser, and water parameters, such as dissolved inorganic carbon, total alkalinity, nutrients and oxygen were also measured.
Moritz Nusser is removing sediment from the mesocosm to sieve out burrowing animals. After sieving, the sediment was re-added to the mesocosm, ensuring that only the animals intentionally added for the treatments remained during the experiment. Photo: Sara Westerström
At the end of the experiment, the researchers collected all the plants and animals for examination and took sediment samples from the mesocosms. Further laboratory work and data analysis are needed to examine the results in more detail. However, a few preliminary observations can already be made.
“The preliminary results suggest that the animals' burrowing in the sediment increased methane emissions,” says Moritz Nusser. ‘From our observations, it also appears that the different treatments affected the growth of Stuckenia.”
“Hopefully, these experiments will provide new insights into the impact of animals on greenhouse gas emissions and how this may change in a warming climate,” adds Sara Westerström.
Stockholm University's new graduate school in marine, climate and environmental issues is directed towards students from diverse disciplines, interested in understanding their own research in a broad and interdisciplinary context.
The Centre for Coastal Ecosystem and Climate Change Research (CoastClim) is a multidisciplinary strategic partnership and research infrastructure project between Stockholm University and the University of Helsinki. The research within CoastClim evaluates the links between coastal biodiversity, carbon cycling, and climate feedbacks.
