The National Aquarium and its Animal Care and Rescue Center will be closed through April 26 in response to COVID-19 (Coronavirus). CLICK HERE for more information.

A Blue View: Acidification and Animal Behavior

The carbon we burn each year doesn’t just end up in the atmosphere; about one-fourth of it dissolves in the oceans, increasing the acidity of our waterways. That includes the Chesapeake Bay, where waters are acidifying three times more quickly than the open ocean. Add pollution to the mix, and you have a recipe for disaster.

Published January 19, 2016


The Bay’s complex food web is facing threats from the changing conditions of its waters. Research shows acidification can have alarming effects on two of the estuary’s most iconic inhabitants: the blue crab and the oyster. One study tested growth of oyster larvae in water containing high levels of acidity—levels, it should be noted, that are expected to occur this century. The results? Shells grew at only one-quarter the speed they did in low-carbon conditions, and they contained less calcium.

This could present a real problem for an oyster population that’s already diminished to 2 percent of what it was in colonial times. On a bigger scale, this could lead to trouble for the Bay itself. Oysters keep the Chesapeake clean and serve as a home for crabs and fish.

Meanwhile, highly acidified waters could beef up one of the oyster’s biggest predators: the blue crab. A 2009 study found that Chesapeake blue crabs grow almost four times faster in high-carbon conditions. When these crustaceans absorb the Bay’s carbon pollution, they molt more quickly and emerge bigger and possibly stronger, making them more challenging prey and fiercer predators.

In other words, while oysters are struggling to survive in the Bay’s altered state, its predators are thriving in it, establishing a dangerous ecosystem imbalance. And oysters aren’t the only ones. The population decline of several of the Bay’s fish species—including striped bass, American shad, alewife, menhaden and herring—has been linked with acidification.


So, what's the good news?

Oysters might be facing major challenges, but they also have a secret weapon to combat acidification: their shells. When their shells break down and dissolve, they release calcium carbonate—a base and the active ingredient in the antacid Tums—into the water, helping to balance out the acidic environment. This is just one of the reasons oyster reef restoration is so critical to protecting the Chesapeake Bay.

Your daily actions can help create a brighter future for the Chesapeake Bay and its inhabitants. By reducing your carbon footprint, you can contribute to the fight against acidification. Your commute is a great place to start making changes. Burning fossil fuels sends carbon dioxide into the air and ultimately into waterways, compounding the harmful effects of climate change and acidifying waters.

Reduce your impact by purchasing local products and taking mass transit, walking or biking whenever possible. You can also decrease your household energy consumption by lowering your thermostat, turning off the lights when they’re not in use and replacing incandescent lamps with fluorescent bulbs. The Bay—and your wallet—will thank you.

Episode Transcript

Imagine if the air you breathed changed your behavior. You might become reckless or disoriented, even experience loss of sight or sound. Yet, what if you had to breathe that bad air anyway, just to survive? This is a scenario that many fish and other aquatic animals could actually face in the near future, with the very seawater that they rely on to exist.

The ocean’s acidity is 30 percent higher today than it was before the Industrial Revolution began a mere 200 years ago. That transformative era of intensive agriculture, manufacturing and transportation has caused the amount of carbon dioxide emitted into the air to skyrocket. And, since our life-giving ocean is known to absorb more than a quarter of the atmosphere’s CO2, the impact of all that greenhouse gas is being felt in our planet’s underwater habitats.

Worse, when CO2 dissolves in water, it forms carbonic acid, causing the pH value of the oceans to drop. This rapid increase in the ocean’s acidity, called acidification, is not without consequence. Researchers have discovered it hinders the development of everything from corals and shellfish to sea urchins and fish eggs. Scientists are now finding it can even alter brain function in marine creatures, causing unusual shifts in behavior.

For example, consider the clownfish—Nemo’s namesake. Scientists found that as the water’s acidity rose, clownfish began to act in an odd manner. Instead of remaining close to their anemone home as they usually do, they began throwing caution to the water and swimming farther from safety. This, in turn, increases the risk of becoming someone’s meal. Even their own sense of smell couldn’t be trusted, and rather than flee from the scent of predators, clownfish in highly acidic waters were attracted to it.

Acidification has also been shown to impair the vision of spiny damselfish, inhibit the ability of snails to reattach themselves when dislodged, make rockfish more anxious, and cause hermit crabs to retract into their shells more slowly when encountering potential predators.

So, how is acidification getting into their heads? A popular theory revolves around GABA, a neurotransmitter that modulates activity in the brain and nervous system of nearly all animals, including humans.

Scientists hypothesize that the increase in CO2 prevents the GABA receptor from working properly, resulting in changes to an animal’s cognitive capacity. If this theory checks out, it could spell trouble for whole classes of organisms, since this particular receptor exists in the brains of both vertebrates and invertebrates.

Acidification has continued to escalate over the centuries, though only in the relatively recent past have we begun to understand the complex and significant changes now underway. Some projections show surface oceans waters becoming nearly 150 percent more acidic by the year 2100, a pH level that hasn’t been experienced for more than 20 million years.

Although acidification is not going away, the good news is that there is still time to address its effects. A study by scientists at Stanford University recently noted that it’s neither too late, too costly nor too complicated to counter the impact of ocean acidification—not yet. The researchers outlined numerous commonsense strategies, both local and regional, to mitigate and adapt to the changing environment.

Scientists and policy-makers are joined in this fight through NOAA’s Ocean Acidification Program, part of a broader U.S. research effort to increase our understanding of this shift in our ocean’s chemistry. Here in Maryland, a forward-looking law was just passed to empower a task force to study this critical issue and its effects on our state’s waterways, and to propose solutions. All are a good start.

Previous Post

Featured Stories

Calypso header Remembering Calypso

We’re looking back at Calypso’s incredible life and reflecting on the many ways she impacted the lives of those who knew her best.

Read the full story

octo header No Hands? No Problem: Tool Use Among Aquatic Animals

Aquatic animals are resourceful—just like humans, when they can’t solve a problem, they can look to the world around them ... and fashion tools!  

Read the full story

Related Stories

A Blue View: Shark Navigation is All in the Nose

Published June 28, 2016

A Blue View: Oyster Gardens

Published June 21, 2016