As our climate changes and more CO2 enters the atmosphere, the oceans are becoming more acidic. Now, scientists have found that young sea stars from the Baltic Sea suffer more from the effects of ocean acidification than adults.

Young individuals of a species are often more sensitive when it comes to environmental stress. As our oceans acidify, it's important to see how these individuals might react. That's why the scientists took a look at the sea star Asterias rubens.

The researchers conducted a long-term laboratory experiment with the sea stars. They simulated three different levels of acidification that could be reached in the Baltic Sea within the coming decades. The scientists found that even with only a slight increase in acidification, young sea stars grew more slowly and ate less. Adult sea stars, in contrast, were only affected at significantly higher acidic conditions.

These sea stars are actually some of the most important benthic species in their ecosystem. They keep the mussel population under control as predators. This means that if the sea star population suffers from ocean acidification, it can impact the entire ecosystem.

Currently, the scientists aren't sure whether the majority of young sea stars develop poorly under elevated CO2. Yet the study did show that the sea stars didn't store less calcium carbonate in their skeletons under acidification. This hints at the theory that the sea stars may grow less because they need more energy to form sufficient calcium carbonate. In addition, the fact that they eat less may show that the acidic water affects their digestive enzymes.

There was, however, some good news. The scientists found that some individuals grew well even under highly acidic conditions.

"If these tolerant animals succeed, sea stars could possibly adjust to new environmental conditions," said Yasmin Appelhans, the first author of the new study, in a news release. "For some species, there are already indications that an adaptation by evolution is possible. Whether this also applies to the sea stars should be investigated in the future. At the same time, it is important to verify the observations from the lab under more natural conditions."

The findings are published in the journal Marine Ecology Progress Series.