The direct chemical effect of our CO2 emissions on our planet’s oceans gets far less attention than the indirect effects caused by global warming. But CO2 lowers the seawater’s pH—known as “ocean acidification”—and this has been shown to be a serious problem for many species. Acidification makes it harder for critters with calcium carbonate shells to grow them, and it even changes the way fish behave.
The majority of studies that have looked at ocean acidification’s impact have fallen into two basic categories: laboratory experiments with carefully isolated conditions and species, and surveys of life at natural CO2 seeps on the seafloor. Each category has drawbacks and advantages. Lab experiments are carefully controlled and can provide unambiguous results. Surveys at natural CO2 seeps can integrate more processes, like species interactions or adaptation over generations. But it’s also true that seeps are surrounded by “normal” ecosystems that could be lending support.
A group of University of Adelaide researchers led by Silvan Goldenberg set out to help fill in the span between those two categories by designing controlled experiments that stepped up the ecological complexity. In 1,800 containers called “mesocosms,” the researchers combined species to form tiny ecosystems. The stars of the show were eight species of fish and shrimp, which swam among a rich supporting cast of over 90 other species—everything from algae and microbes to predators.