Shelled pteropods, commonly known as sea butterflies, are tiny, free-swimming sea snails, which are an important part of the marine ecosystem. They are also vulnerable to climate change as their shells are sensitive to ocean acidification. Now, a team of researchers from the UK has examined life cycles of two sea snail species. They found that one is less vulnerable to changes in the Southern Ocean than the other. This can affect pteropods on a population level and in turn impact the marine ecosystem.