12 September 2023, by RTG2530
What role do fish play in the carbon cycle of the Elbe estuary? Doctoral researchers Jesse Theilen, Raphael Koll and Elena Hauten want to answer this question in their research projects of Research Training Group 2530. We accompanied them on their research work in the field.
The morning sun is shining through a few small clouds in the sky, while it is still quiet on the Elbe - only a few small sailing boats cross the path of the fishing vessel Ostetal, which is slowly sailing through the water. On board however, there is a lot of activity: While the crew of the fishing vessel takes care of the ship's equipment, Elena Hauten, Raphael Koll and Jesse Theilen sort, count and measure the current catch.
The research projects of the three doctoral students are part of the Research Training Group 2530. They want to explore the role fish play in the carbon cycle of the Elbe estuary.
"I am looking at the feeding ecology, growth and migration behaviour of the most important fish species in the Elbe," says Jesse Theilen. "By doing so, I want to find out what the most important prey of the fish species is and how size growth is influenced by prey." He examines the individuals and analyses their stomach contents and, among other things, their size.
The aim of Raphael Koll's project is to analyse the stress response of selected fish species in the Elbe estuary. "The basic mechanism of any organism to cope with environmental influences is the change in gene expression. I link these changes in gene expression to factors in the environment such as salinity, temperature or oxygen of the water. I also study the interaction between the fish and its microbiome, i.e. the composition of the microbes on the fish," he explains.
The smelt is the most common fish species in the Elbe estuary. It spends most of its time in marine waters and comes to the estuary in spring during spawning season. In her doctoral project, Elena Hauten is paying special attention to these migratory fish. "They transport a lot of carbon and are therefore biotic carbon vectors in the estuary," she says. "Among other things, I am analysing their food web and studying the muscle tissue from the fish species we catch most often."
At the end of the trip, the three Doctoral Researchers will have collected various samples at five different sites along the Elbe between Cuxhaven and Hamburg. It takes them several days to cover the distance and collect the samples.