We've known for a while that the ocean is rapidly becoming too acidic for some forms of marine life to survive. We know that this is caused by continued rising emissions of carbon dioxide, which dissolves from the atmosphere into the ocean to form carbonic acid, which in turn dissolves/corrodes calcium carbonate-based coral reefs and shellfish.
Now we also know that ocean acidification does more than break down marine skeletons -- it can actually cause behavioral changes in individual organisms. Simply stated, ocean acidification is making fish anxious -- or, at least, anxiety as we measure it in fish.
Scientists from UCSD's Scripps Institution of Oceanography and Canada's MacEwan University recently published this surprising finding in Proceedings of the Royal Society B: Biological Science. But what does it mean for fish to be anxious? According to this study, all it takes is observing how much time the fish choose to spend in dark versus light areas of their habitats. The test subjects were juvenile rockfish, whose natural environments -- kelp forests -- off the California coast offer varying levels of shade and sunlight. The researchers put a control group of rockfish in a tank with "normal," or unaltered, seawater and observed the fish moving continuously between the light and dark areas of the tank. They put a second group of rockfish in a tank with seawater of elevated acidity, meant to approximate the expected pH of the ocean 100 years from now, and observed something different.