"Using stable isotopes to identify sustainable food fish in a coastal ecosystem on Gotland"
Adrianus Both finished his time as a Blue Food postdoc at Uppsala University in the fall of 2023. He now works at IVL Swedish Environmental Research Institute with a project on competition between bivalves for food: "Do invasive and native bivalves compete for food resources? The role of detritus in supporting sustainable aquaculture and invasive species management."
Since August 2021, Adrianus Both has been working as a Blue Food researcher at Uppsala University on Gotland. His project is about finding out what the marine food chains look like in the sea around the Isle of Roses. The goal is to find out which fish species can be used in a sustainable way.
Plants and animals that move through the food chain when eaten by other organisms are made up of elements such as carbon, nitrogen and sulphur. These elements can occur in different versions, called isotopes, which have different numbers of neutrons in the atomic nucleus. When a substance is consumed, different atoms change in different ways. For example, carbon is relatively stable while nitrogen atoms become heavier as they move up the food chain. This means that the composition of isotopes can reveal what different organisms eat.
'It's a bit like mixing paint colors,' says Adrianus Both. "If we imagine that the isotope composition of phytoplankton corresponds to yellow and seagrass corresponds to red, we can conclude that an 'orange' crayfish eats both."
Bugs tell us about fish that are spreading.
Since Adrianus Both started at Uppsala University in August, he just missed the summer sample collection. But a fellow PhD student had collected material in two bays on Gotland. He has helped her sort through the material and has also been able to use some of it in his own research. The samples include snails the size of a peppercorn, shrimps, mussels, cockles, small shellfish living on seaweed, filtering animals and plants. After the samples are sorted, they are dried and powdered, oil is added and then the preparations are sent to the UK where they are evaporated and the isotope values are analyzed. Depending on the substance being studied, different amounts of samples are needed, but either way a lot of organic material is collected.
In the project, Adrianus Both studies the fish species id and spigot, both of which are omnivores. In recent years, the spike has taken up more space and one theory is that competition has caused the id to switch to a more plant-based diet.
I would also like to investigate whether id and spike change their diet when they get bigger. If so, perhaps we should fish them harder to benefit the small perch and pike that we want to protect. With more knowledge about the food web, we will have a better basis for which fish we can fish and how we can counteract the problems of different species.
The ultimate goal of the project is to find out where our food fish get their food from in order to better know what kind of fishing and supporting measures are sustainable. However, the exact route and the research questions to be answered are not entirely clear, but will adapt to the results he gets along the way.
Big differences between the Atlantic and the Baltic Sea
Adrianus Both comes from the province of New Brunswick on the west coast of Canada, where he has studied mussel farming. He participated in a course on sustainable aquaculture in Sweden a few years ago, but much here is new to him, not least how the Baltic Sea differs from the Atlantic.
The mussels here are very small, because the salinity is so low, it's a challenge. Many species are new to me and there is much more vegetation on the coast than I am used to.
Unlike the other young researchers in Blue Food, Adrianus Both is a postdoc. This means that his project duration is two years and the project is expected to be completed already in the fall of 2023.
Supervisors
Gunilla Rosenqvist, Uppsala University
Lina Mtwana Nordlund, Uppsala University