Temperatures are increasing more rapidly in the Baltic Sea compared to the global ocean. Projections are that temperatures will rise up to 3 °C to 5 °C during this century. To respond to these climate changes, species will either adapt, move or go extinct. In a new study, it looks like the copepod Eurytemora will cope well, from the Stockholm Archipelago in Askö at least:

- This is good news, since copepods are an important food source for some of the world’s most important fisheries, such as herring, sprat and anchovies, says Monika Winder, professor at Department of Ecology, Environment and Plant Sciences (DEEP).

The copepod Eurytemora. Photo: Konrad Karlsson.

In the new study scientists exposed copepod populations from different areas such as the Gulf of Riga and the north of the Baltic Sea to higher temperatures in the lab. The study showed that the sensitivity of populations to environmental stressors, such as temperature change, salt content of the water or quality of the food varies depending on their local origin and how they are adapted to the condition.

- It turns out that the sensitivity of the copepod varies depending on stress factors specific to their particular local environment. This means that the populations develop to cope with different environments, says Konrad Karlsson, who conducted the experiments during his PhD education at DEEP.

For example, the population from the northern Baltic Sea are more sensitive to climate warming and the population from the Gulf of Riga are more sensitive to changes in food if changes occur together with increased temperatures:

- We need to make sure that fish prey, such as copepods can feed on high quality algae that in turn makes them more resistant to an increase in temperature, says Monika Winder.

Algae cultures. Photo: Monika Winder.

For nature to provide high quality algae for the copepod to feed on, we need to reduce eutrophication, which causes greater blooms of cyanobacteria, a poor quality food source. There are thus other threats to healthy populations of copepods that need to be taken care of, since it is often the combination of different factors that affect them the most:

- We need to make sure that all different populations of copepods in the Baltic Sea are healthy when the temperature rises due to climate change. This is because if a locally adapted copepod population goes extinct, other populations would have to have to first evolve and develop specific adaptations to take their place, says Monika Winder.

The local adaptations for copepods include for example size or number of eggs and it could potentially take years for copepods to adapt. If a local population goes extinct and no copepods can take its place, firstly fish lose their prey and it provides opportunities for invasive species to establish.

- The good news is that central Baltic Sea populations look like they are going to cope and adapt to increasing temperatures, finishes Monika Winder.

The study “Adaptation potential of the copepod Eurytemora affinis to a future warmer Baltic Sea” is published in the scientific journal Ecology and Evolution DOI: https://doi.org/10.1002/ece3.6267