Bottom fauna in Bothnian Sea adapts to new diet

A recently published doctoral thesis shows Monoporeia affinis, a small, benthic amphipod and key marine species in the Baltic Sea, benefit from eating cyanobacteria. This is good news as cyanobacteria will both increase and spread northwards with the ongoing climate change. But the thesis also showed that amphipods living in the Bothnian Sea seem to be particularly sensitive to environmental toxins.

As well as being important prey for fish, amphipods also perform other important functions in the ecosystem by feeding on algal blooms and oxygenating the sediment through their burrowing activities. Photo: Matias Ledesma

"We already knew that amphipods from the Baltic Sea proper, where cyanobacterial blooms have occurred for thousands of years, can eat cyanobacteria. The new finding is that amphipods in the Bothnian Sea, where the toxic cyanobacteria were not present up until now, also can live well on this diet," says Matias Ledesma, who wrote the thesis at the Department of Ecology, Environment and Plant Sciences.

The Baltic Sea has undergone major changes in recent decades and benthic animals are particularly exposed, both to environmental toxins that accumulate in bottom sediments and to changes in food availability due to climate change. In his doctoral thesis, marine ecologist Matias Ledesma investigated how amphipods, key species in the Baltic Sea ecosystem, react to these changes.

Biomarkers show what they have eaten

Using chemical diet biomarkers, in the form of carbon and nitrogen isotope analyses, Matias Ledesma has been able to see what the amphipods have been eating and whether individuals within a group are eating similar things. If all individuals eat very similarly, there is little variation in isotope composition within the population.

Research shows that amphipods grow best when they are fed a combination of cyanobacteria and diatoms. This means that the small animals will be able to adapt to the new diet: an increasing amount of cyanobacteria.

Sampling in winter weather conditions

Environmental monitoring in winter. Photo: Matias Ledesma

Matias Ledesma's research has been part of a unique environmental monitoring programme, funded by the Swedish Environmental Protection Agency and carried out annually since 1994. In late winter, when females carry their young in a brood pouch, he has been able to monitor embryo development and malformations in the amphipods. Sampling in winter weather may not be convenient, but it allows for visual inspection of the embryos carried by pregnant females.

"It's exciting to have had the opportunity to be part of the monitoring program and at the same time research the environmental effects on amphipods," says Matias.

As expected, amphipods exposed to pollution had reduced reproductive success, but the thesis also shows that other factors such as diet and temperature have an impact. The greatest negative effects of environmental toxins can be seen in amphipods from the Bothnian Sea.

Better environmental permit assessments

The Monoporeia affinis. Photo: Matias Ledesma

Matias Ledesma hopes that his thesis will be of practical use and benefit to the environment and fauna of the Baltic Sea.

The results of the thesis can be used for ecosystem-based management of populations and to improve integrated environmental assessment.

The thesis has just been printed and the defense will be held on 31 of March

The thesis is accessible here: Coping with environmental change: Lessons from isotope studies in a sentinel species

Text: Jenny Rosen