Not just the oceans, freshwater acidification is happening too
If ocean acidification is "climate change's equally evil twin" then freshwater acidification is the forgotten black sheep of the family.
Credit: Velvetfish/iStock
As CO2 levels increase in the atmosphere, dissolved CO2 in water bodies increases, reducing the pH. Ocean acidification has been well documented to cause all sorts of issues, from the collapse of zooplankton, a primary source of food for many marine systems, to damaging fish eyesight, or messing with the minds of everything from fish to snails, changing how they respond to predators.
The situation for freshwater ecosytems though, isn't well understood. In captivity, acidification can cause havoc with freshwater species. A 2015 study showed that captive grown salmon were smaller in size, less able to take up oxygen, and showed changes in behavior that made them more susceptible to predators. But the extent to which freshwater acidification is happening, and what effect it's having on ecosystems, is unknown. "Freshwater ecosystems have been largely overlooked," says Linda Weiss at Ruhr-University Bochum in Germany.
To investigate, Lina Weiss and her team analysed 35 years of monitoring data from four freshwater reservoirs in Germany. They showed a trend of increasing amount of dissolved CO2 and lower pH. The pH of the reservoirs dropped 0.3 over that period which is a much faster rate than seen for acidification of the ocean.
To look at impacts on the ecosystem they looked at water fleas, small crustaceans called Daphnia. They're a critical part of the ecosystem, as they're food for many larger animals. Water fleas may be tiny, but threaten them with being eaten and they'll whip up some neck-teeth to throw you off. Neck-teeth are these tiny helmet and spike like structures that the water fleas produce when they detect the chemical signatures of predators in the water. As dissolved CO2 concentrations increased in the reservoirs, the water fleas were less able to detect the chemical cues of their predators and less likely to form these neck-teeth defences, making them more vulnerable.
Daphnia produce defensive "neckteeth" in the presence of predators (right). In freshwater with high levels of dissolved CO2 they fail to produce the same structuers (left). Credit: Sina Becker
The broader effects this has on the freshwater communities is unclear at the moment. The next stage is to get data from more freshwater systems around the world.
"We now want to know the global degree of this phenomenon," Weiss says.
Paper in Current Biology: http://www.cell.com/current-biology/fulltext/S0960-9822(17)31655-X
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