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New Study: Carbon Dioxide Pollution Fuels Fish Kills

Scientists have long known that burning fossil fuels increases global temperatures by wrapping the world in an insulating blanket of greenhouse gases.

Carbon dioxide melts polar ice and also expands the volume of the oceans, driving up sea levels and causing coastal flooding.

But there is a second – invisible -- impact of fossil fuels on oceans: Carbon dioxide reacts with water to form carbonic acid.  Since the Industrial Revolution, the acidity of the oceans has jumped by a third – weakening the shells of clams, oysters, coral and plankton.

A new study, published yesterday by scientists at the Smithsonian Environmental Research Center in Edgewater, Maryland, suggests this acidification may also be having an unexpected impact on the Chesapeake Bay and other waterways: More frequent fish kills. 

Fish kills often stink up Baltimore’s Inner Harbor and the Bay in the summer when high nitrogen and phosphorus pollution levels feed algal blooms that suck oxygen out of the water at night, making the fish suffocate.

The new research, by Seth Miller, Denise Breitburg and colleagues at the Smithsonian, found that a common species of small fish – the silverside – gasps for oxygen and then dies more quickly in water with oxygen at levels that might normally sustain it when the fish are also subjected to slightly more acidic water.

“We caught the fish right here in the Rhode River, and then we lowered oxygen and increased the acidity, and just watched the fishes’ response,” said Breitburg, senior scientist at the Smithsonian Environmental Research Center.

In case you’re wondering what exactly that response was the laboratory with the tanks of water used for the experiment is called the DOOM lab – the Dissolved Oxygen Oyster Mortality lab.  Or, more commonly, the “Room of Doom.” And it certainly was for the poor silversides.

“So when acidity is high, and oxygen is low, fish were much more sensitive to low oxygen,” Breitburg said. “So they actually headed up to the surface to try to gulp that water right at the very surface layer in contact with air when oxygen in the water was not quite as low as what would normally take to drive them to the surface.  That really exposes them to bird predation, for one thing.  But then, for the ones we just kept lowering the oxygen on, they also died at higher oxygen concentrations than would otherwise affect the fish.”

Alright, so, who cares about silversides, anyway?  It’s not like it’s a Chesapeake tradition to invite your family and friends over to eat a big bucket of these minnows. For one thing, what is happening to the silversides could well be happening to many other species of fish.  And although people don’t eat silversides, many other animals do.

“Well, one of the things with silversides – my postdoc, Seth Miller, who was the lead author on the paper – loves to describe them as the popcorn of the bay, because everything eats them,” Breitburg said. “Fish eat them, raccoons eat them, birds eat them, so if they’re affected, then the effects on them can really be translated throughout the food web.” 

One implication of the study, published in the journal Marine Ecology Progress Series, is that the oxygen water quality standards set the government throughout the Chesapeake Bay and other waterways may not be protective enough for fish survival because they don’t take into account the increasing acidification of our waters.

But a broader implication is that everything is linked. You may not think about it, but driving your SUV may be contributing to fish kills as well as floods.  There is an answer: Drive less, conserve energy at home, and vote for politicians who support solar and wind energy and strong regulation of pollution.  

Tom Pelton, a national award-winning environmental journalist, has hosted "The Environment in Focus" since 2007. He also works as director of communications for the Environmental Integrity Project, a non-profit organization dedicated to holding polluters and governments accountable to protect public health. From 1997 until 2008, he was a journalist for The Baltimore Sun, where he was twice named one of the best environmental reporters in America by the Society of Environmental Journalists.