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Fish on Acid

Fish on Acid Juvenile damselfishes were less able to detect predator odor than fishes from a control coral reef.
Photo Credit: Danielle Dixson

Fish in acidified waters exhibit strange and often reckless behaviors.


Transcript

Fish behaving strangely. I’m Bob Hirshon and this is Science Update.

Acidifying ocean waters, driven by climate change, may cause bizarre, self-destructive behavior in some fish. This according to a new report by Georgia Tech marine biologist Danielle Dixson. Her team collected fish from a naturally acidic reef in Papua New Guinea. She says most fish avoid waters that predators recently swam in. But these fish did the opposite.

Dixson:
They were attracted to the predator almost 100 percent of the time. So they chose to spend their time in the water that contained the predator odor, as opposed to the offshore water that had no predator odor in it.

Fish in acidic waters also venture further from safety, and re-emerge more quickly after they do hide. Dixson notes that climate models predict that by the year 2100, the entire ocean may become as acidic as this reef. That may make some fish a danger to themselves. I’m Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

As humans pump more and more carbon dioxide into the Earth's atmosphere, the atmosphere traps heat, causing a wide range of effects we know as global climate change. However, increased carbon dioxide (CO2) in the atmosphere doesn't just affect the climate.  It also causes a phenomenon called ocean acidification.

As carbon dioxide concentrations rise in the atmosphere, they also rise in the oceans, because about 25 percent of the atmosphere's CO2 dissolves in the oceans. When dissolved carbon dioxide mixes with water, several chemical reactions occur that make the water more acidic. According to the National Oceanic and Atmospheric Administration, the oceans are 30 percent more acidic today than they were around the start of the Industrial Revolution. That's a faster rate of acidification than the planet has seen in at least 20 million years, and far too fast for marine ecosystems to adapt. Furthermore, scientists project that if human CO2 emissions continue as they do now, the ocean's surface waters will be 150 percent more acidic by the end of this century.

Researchers are already seeing the consequences of today's ocean acidification, in the form of damage and corrosion to coral, and reproductive failures in shellfish like oysters. In this study, the researchers looked at an unusual part of the ocean that's already as acidic as the entire ocean may become by 2100. That's because of natural undersea CO2 vents that pump extra carbon dioxide into a relatively limited area.

As you heard, the fish the researchers studied behave very strangely in these waters. Rather than avoid waters that smell like predators, the fish actually preferred them! The fish also showed a decline in self-protective behaviors, like taking shelter and staying close to their home.

It's not clear why this happened, but the researchers believe that the fish's sense of smell may be seriously malfunctioning under the acidic conditions, resulting in an inability to avoid predators. Right now, there's no evidence that this is actually lowering the fish's populations, perhaps because these pockets of excess CO2 are surrounded by waters of more normal acidity (by today's standards), and fish are able to move freely from one area to another. But that won't be true if the entire ocean becomes much more acidic. And if just one species of fish has such a strange reaction to acidic water, it's possible that marine life may be profoundly affected by acidification in all sorts of unexpected ways.

Now try and answer these questions:

  1. What is ocean acidification?
  2. How is the acidification of the reef these researchers studied unusual?  Why is that useful?
  3. What behaviors were different in fish exposed to the acidic waters?
  4. What are some of the potential risks of these behaviors, especially as the entire ocean becomes more acidic?

You may want to check out these related resources:

The Science Update Changing Oceans describes some of the broader effects of climate change on the world's oceans.

The 12-minute video Communicating and Learning about Climate Change, produced by AAAS, features a number of experts on global climate change talking about its impacts to our planet.


Going Further


For Educators

The Science Update Changing Oceans describes some of the broader effects of climate change on the world's oceans.

The 12-minute video Communicating and Learning about Climate Change, produced by AAAS, features a number of experts on global climate change talking about its impacts to our planet.


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