John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Acidic oceans are stressing out fish, say researchers, and that's not good for global food security.
Seems like humans aren't the only ones anxious because of climate change. Beneath the briny waves could lie legions of stressed-out fish, whose bodies aren't up to coping with the ongoing acidification of the oceans.
Scientists have known for some time that the lowering of the oceanic pH level – the result of humans pumping gigatons of CO2 into the atmosphere – isn't great for marine life. The CO2 reduces the amount of calcium-based minerals in the water, creating difficulties for animals with shells like oysters, urchins, clams, and plankton. The impact to corals is particularly worrisome, as they lose the ability to rebuild themselves after being harmed by other sea creatures and increasingly warmer seas. The death of corals spells difficulty for the animals that live in them, thought to number up to 9 million species.
But now marine experts believe that acidic oceans are screwing with fish, too. California and Canadian researchers provided the evidence for this in a new study advancing the delightful field of fish behavioral neuroscience. Their investigation uncovered a "potential negative effect of ocean acidification on fish behavior," according to the press people at the Scripps Institution of Oceanography at UC San Diego, "that can possibly affect normal population dynamics and maybe even affect fisheries."
Their experiment involved a few steps: First, they wanted to see how stressed fish behave. So they doped a bunch of juvenile rockfish with an anxiety-provoking drug, and watched what happened. The medicated fish turned out to be skittish, seeking out and hiding in the dark places in their tank, whereas a group of non-drugged fish circulated widely in both light and dark areas.
Next, the scientists increased the acidity in one tank to match the oceans' expected pH level by the end of the century. They used tracking cameras to monitor what came next: While the fish in "normal" water swam all over the place, the ones in acidic water again sought out the dark corners. Here's the camera showing the movements of the control group:
And here's the erratic swimming of the acid-bath fish:
Fish left in the acidified water for an entire week were "significantly more anxious than their normal seawater counterparts," the researchers report. They continued to show signs of distress 12 days afterward (the fish, not the researchers) even after being transplanted to regular water.
The scientists attribute this weird behavior to a chemical imbalance in the fish's brains. Brain damage is not good for the animals, obviously, and it could also wind up hurting marine industries as addled fish would likely have trouble surviving and reproducing. That's not great for California's rockfish business, or any other place that relies on fishing to support its economy. Explains Scripps marine biologist Martín Tresguerres:
Tresguerres says anxious behavior is a concern for juvenile rockfish because they live in highly dynamic environments such as kelp forests and drifting kelp paddies that offer variable lighting and shading conditions.
"If the behavior that we observed in the lab applies to the wild during ocean acidification conditions, it could mean that juvenile rockfish may spend more time in the shaded areas instead of exploring around,” said Tresguerres. “This would have negative implications due to reduced time foraging for food, or alterations in dispersal behavior, among others.”
But it could be the days of stressed-out fish are nigh. Since the Industrial Revolution, the oceans' surface waters have fallen about 0.1 pH units, according to NOAA. That doesn't sound like a big deal until you realize the pH scale is logarithmic – that change in chemistry means the seas are 26 percent more acidic. And the rate that they're becoming that way is possibly faster than anything in the previous 300 million years, climate and marine researchers warned last month:
People who rely on the ocean’s ecosystem services are especially vulnerable and may need to adapt or cope with ocean acidification impacts within decades. Shellfish fisheries and aquaculture in some areas may be able to cope by adjusting their management practices to avoid ocean acidification impacts. Tropical coral reef loss will affect tourism, food security and shoreline protection for many of the world’s poorest people.