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As climate change warms the air, the same is happening underwater – sometimes even faster.

Temperatures in the Chesapeake Bay have been going up for three decades, driven by several factors linked to climate change, researchers say. That’s expected to continue even while humans work to curb carbon emissions.

Resulting effects on the delicate ecosystems that comprise the bay could impact everything from what ends up on your dinner plate to when you can go swimming.

Scientists and officials around the bay’s watershed are now calling for those in power to pay close attention to the impacts of the ongoing changes — and invest in solutions that mitigate them.

Warmer waters have “many, many cascading potential effects,” said Pam Mason, senior research scientist at the Virginia Institute of Marine Science.

Mason was among dozens of environmental experts who convened recently over a series of workshops to discuss those effects for the Chesapeake Bay Program, a massive partnership of nonprofits, academics and governments that works to restore the bay.

“It was illuminating in many respects because a lot of people have had specific pieces of the picture, but they hadn't seen it all pulled together,” said Bill Dennison, a marine science professor with the University of Maryland Center for Environmental Science who co-chaired the workshop.

“The enormity of the issue became evident ... And the ramifications of this were far reaching.”

Life in and around the water

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Photo by Katherine Hafner 

A blue crab in the Lynnhaven River near the mouth of the Chesapeake Bay.

The way warming affects marine life is complex and interconnected, Mason said. 

For one, warmer water is more likely to be acidic. That leads to fewer of the carbonate ions and minerals needed for shelled creatures like oysters and crabs to build their skeleton homes.

If they end up with thinner shells, they could be more vulnerable to predators, and eventually not live long enough to reproduce, Mason said. 

“And then we don’t get baby oysters and clams to replace the ones that die or get harvested,” she said. “So ocean acidification is one piece of the puzzle.”

Higher temperatures also spur the growth of harmful bacteria and algae which take over the water’s surface and block out sun from reaching life that needs it below.

Areas of the bay already see these “red tides” or algal blooms periodically in warmer months. They cause “dead zones” with not enough dissolved oxygen in the water.

Less oxygen is one of warming’s most concerning impacts, Mason said. Warmer water doesn’t hold as much of it, and fish, shellfish and underwater plants need it to survive.

Experts call it the “habitat squeeze,” Dennison said. The surface water is too hot but the bottom doesn’t have enough oxygen.

“And so the zone at which you can survive in the middle is shrinking,” he said.

Eelgrass is already suffering, according to the new report. Numbers of the underwater grasses are declining, especially closer to Hampton Roads in the southern part of the bay.

Without “drastic improvements in water clarity or a reversal of warming trends,” the authors write, viable populations of eelgrass will likely be eliminated from the bay, along with the food and habitat they provide to many species.

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Photo by Katherine Hafner

Eelgrass on the Eastern Shore.

Dennison said it’s not just overall temperatures rising, but also the frequency and severity of heat waves.

“We saw up close and personal the heat wave effects in 2005 and 2010, when late summer we get these long periods of still weather and sweltering heat and the grass in the southern bay was dying back,” he said. “So we've known for some time that these event-driven things were causing widespread ecological implications.”

The new report says there are some potentially positive impacts of warming on certain species. Blue crabs could expand their habitat range northward. 

But Mason noted that warming can still interrupt other aspects of the species’ life, such as when food becomes available. It’s important to look at the larger picture, she said.

The toxic algal blooms fueled by warmth can also impact people’s ability to interact with the bay, Mason said.

Time and again, residents note in surveys that they value the Chesapeake.

“They either swim or they kayak or they boat or they fish,” Mason said. “And those kinds of activities are going to be adversely impacted by the increase in temperature.”

The “red tides” could block off certain areas from recreation or make fish dangerous to eat.

More warmth in the water also means more warmth in the air blowing off the water, compounding local humidity.

Pollution and moving forward

The bay’s leaders “need to take account of the fact that a critical, basic condition—water temperature—has been changing and will continue to do so,” authors of the report wrote.

The jurisdictions and environmental groups that make up the bay program have been working to meet pollution reduction targets set by the federal government by 2025 and acknowledge they won’t reach them on time.

To improve water quality, officials use what are known as best management practices, or BMPs.

The conservation measures are mainly used in wastewater management and agriculture to reduce nutrient runoff, including planting cover crops and limiting how much a farm’s soil is churned up by mechanical digging.

Photo via Chesapeake Bay Program 

A graphic shows long-term temperature changes around the Chesapeake Bay watershed.

One of the new report’s most surprising findings: some of those measures put in place to reduce pollution could be contributing to warming.

Mason said many of the best practices are aimed at storing water.

“Let's say we're in an urban place, (the water) hits the street and it flows through a pipe into a stormwater pond and then sits there for a while till it's slowly released,” she said. “As it sits in that shallow pond, the water temperature goes up.”

She hopes decision-makers can learn from the report and focus on nature-based solutions that help with several issues at once.

Planting trees and greenery along waterways, for example, helps ease pollution while also having a cooling effect.

Dennison said it’s time to rethink our priorities to better prioritize climate resilience.

“The bay of the future is not going to be the bay of yesterday,” he said. “Let’s create a vision of a future bay that is one that encompasses the fact it will be warmer. … We’ve got to be much more aggressive.”