Exploring How Oyster Blue Crab and Spotted Seatrout Populations Respond to Environmental Change

Blue crabs crawl inside a bushel on a boat off the coast of the Smith Island town of Tylerton, Maryland. © JIM LO SCALZO/epa/Corbis

For centuries, the Chesapeake Bay has been a natural seafood factory along the East Coast, and that wealth of marine resources has shaped the area's food culture and history—a 2011Garden & Gun article referred to Maryland crab cakes as "practically a religion." Seafood production also represents a critical portion of the Chesapeake Bay's economic backbone. According to the National Oceanic and Atmospheric Association (NOAA), the commercial seafood industry accounted for $3.39 billion in sales, $890 million in income and almost 34,000 jobs throughout Virginia and Maryland in 2009.

Three species in particular constitute the bulk of the Bay's economic foundation: oysters, blue crab and striped bass. But as temperatures warm and ocean waters become chemically altered, residents of the Chesapeake region might need to reconsider what makes their region so special—and be willing to trade their crab cakes for a new food icon.

"The identity has to change and adapt over time, just like the ecology of a system does," says Denise Breitburg, an ecologist at the Smithsonian Environmental Research Center. "Climate change is a fact, and I hope that we start taking the serious actions that we need to. But even if we start taking those actions, though, we're going to see changes, and there's really no option other than to adapt."

Since the 1930s, the Chesapeake Bay has seen a 2-degree Fahrenheit increase in average water temperature. But temperature increase alone won't necessarily spell disaster for the Chesapeake's marine life, according to scientists like Donald Boesch, professor of marine science and president of the University of Maryland Center for Environmental Science. Instead, it plays into a slew of other factors that could significantly hinder the Bay's historic production levels. "Some of the species, like oysters and blue crabs, do just fine south of us in warmer climates, and so we don't see any immediate threats to them from temperature," he says. "But it will change them in some ways that we don't know about fully."

The blue crab, for instance, is one of the Chesapeake's most recognizable exports. In 2009, the blue crab's dockside harvest contributed an estimated $78 million to the local economy. Blue crabs lie dormant in the winters, seeking refuge from colder water temperatures by burrowing into the Bay's bottom sediments. When water temperatures climb to about 54 degrees Fahrenheit, blue crabs become active enough to crawl into the pots or dip nets of Chesapeake fishermen. The season usually begins around April 1, though fluctuating temperatures in recent years have made the beginning of the season harder to pin down. As winter temperatures increase, the crab's movement patterns might change more significantly, impacting how fishermen track and capture the crabs.

In addition, warming temperatures can decrease the amount of oxygen that can dissolve in water, which could threaten the crabs' ability to survive in the Chesapeake, Breitburg says. This is especially problematic when the effects are combined with water pollution. Each summer, run-off containing excessive amounts of nitrogen from farm fertilizer or sewage encourages algae blooms in the Bay. These blooms create "dead zones" where little to no dissolved oxygen can be found in the water. Scientists have seen these dead zones cause a decline in marine diversity throughout the Bay—and with warming ocean temperatures, the dead zones can only be expected to grow.

While warmer waters lose their oxygen, they also have to contend with more CO2 in the air, which becomes dissolved in the ocean's waters, causing them to become more acidic. In such waters, organisms that produce calcium carbonate shells can't produce those shells as easily, resulting in higher mortality rates. "And more acidic conditions tend to erode the shells that they do build," says Boesch.

That means ocean acidification will be a major threat to the Bay's other quintessential food: oysters. In the late 1800s, when the Chesapeake Bay reached peak oyster harvest, the region was generating between 14 and 20 million bushels per year. Today, due to overfishing and disease, oyster populations are a mere one percent of what they once were. If ocean waters continue to become more acidic, that one percent looks to be in danger.

Warming temperatures might also mean a greater risk of disease for oysters.Perkinsus marinus, a protozoan parasite, has been especially virulent among Chesapeake oysters since the 1980s. The parasite enters their digestive gland tissues, and infected oysters exhibit low reproductive rates and significantly reduced growth rates. Eventually, a buildup of hundreds of thousands of parasites kills the oyster by breaking down its internal tissues and obstructing its hemolymph vessels (the oyster equivalent of blood vessels). The parasite can't infect humans, but it can kill more than half of infected oysters. Recent years have seen an expansion ofP. marinus, which can now be found north of the Chesapeake. "That's very clearly associated with the warming temperatures there," Boesch says.

In addition, some of the Chesapeake's fish will be directly impacted by warming waters. Nearly three-quarters of striped bass, or rockfish, found along the East Coast begin their lives in the Chesapeake Bay—the striped bass is the most popular fish for both recreational and commercial fishing within the Bay, generating $500 million in economic activity. But the striped bass is especially vulnerable to warm waters, and current summer temperatures are already reaching 30 degrees Celsius in very shallow areas. "Surface water temperatures during the summer are already pretty warm for them—warmer than ideal—and if the bottom [of the Bay] is low in oxygen, they wind up not having a lot of habitat that's really suitable for them," Breitburg says of the fish. "If oxygen gets worse and surface temperatures get warmer, that's the kind of species that's really going to have a hard time."

In a century's time, Breitburg says, the Chesapeake Bay will be a very different place from what residents and tourists know today. But as Boesch notes, it's difficult to pinpoint exactly when these changes will become apparent to the casual observer. "Climate change is a subtle thing. It moves in fits and starts," he says. "It sort of creeps up on you, if you will. We are probably already experiencing it."

Today, someone fishing in the Chesapeake might be able to catch a red drum or spotted sea trout, fish traditionally found in the Gulf of Mexico. "They have become more common in the Bay," Boesch explains, "and the commercial fisherman are quite happy with that." Other marine life, such as shrimp, which typically thrive in more southern waters, might become increasingly common in the Bay as well. But shrimp fishing would bring with it an entirely different set of concerns, as wild shrimp are often caught via bottom trawling, which can disturb the seabed and result in excessive bycatch—for every pound of shrimp caught via trawling, fishermen can catch up to 15 pounds of unintended marine life.

If in the coming decades the Chesapeake becomes known for shrimp instead of blue crab, the fishing communities and the policy makers that dictate fishing regulations need to be ready, Breitburg says. "In some ways, the most critical thing is to keep adapting our fishing regulations to the reality of what climate change is doing to the abundance of species in the Bay, and to be pretty nimble about making changes when they need to be changed," she says.

So appreciate those Chesapeake oysters and blue crabs while they last—soon, it might be nothing but shrimp and spotted sea trout on the menu.

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Denise Breitburg spoke about the vibrant culinary history of the Chesapeake on September 11 as part of the Food in the Garden series at the National Museum of American History. The four-part series, which continues with programs on September 18 and September 25, seeks to engage visitors in conversations about food, history and their relationship. This years' programming focuses on four maritime regions affected by the War of 1812: Long Island, the Chesapeake, the Great Lakes and New Orleans. Each event features a moderated discussion with a panel of experts, as well as a sampling of food inspired by the evening's topic. The September 18 event will focus on exotic and invasive species in the Great Lakes, while September 25's event will discuss the cultural significance of New Orleans' marketplaces. Tickets to the event are $30, and include two drinks (courtesy of Green Hat Gin and Distillery Lane Ciderworks) and a plate of historically inspired food. Weather permitting, the events take place outside of the museum within the Smithsonian Victory Garden.

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Source: https://www.smithsonianmag.com/science-nature/what-does-climate-change-mean-chesapeake-bay-180952690/

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