In Chesapeake Bay’s changing ecosystem, blue crab is king

WYDaily.com is your source for free news and information in Williamsburg, James City & York Counties.

Buckroe Beach in Hampton, Va, Jan. 25, 2017.
As water temperatures get warmer in the Chesapeake Bay, scientists say some native species will thrive while other struggle to survive. (Sarah Fearing/WYDaily)

Dozens of feet below the surface of the Chesapeake Bay, the world is changing as we know it.

From the silty ocean floor, to the waves on the Bay’s surface, the marine ecosystem is starting to look different. Acres of the Bay’s brilliant green eelgrass are disappearing, causing blue crab to move into red algae. Habitable waters for native striped bass are shrinking, and populations of southern species, such as spotted seatrout and red drum fish, are growing larger.

In the face of an evolving ecosystem, experts agree many of the differences in Chesapeake Bay marine life can – at least in part – be attributed to a worldwide warming trend.

Over the last three decades, water temperatures in the Chesapeake Bay have increased about 1.5 degrees Celsius, or about 2.7 degrees Fahrenheit, said Rom Lipcius, professor of marine science at the Virginia Institute of Marine Science.

The change means populations of many native sea creatures in the Chesapeake have moved or expanded north in search of cooler water temperatures, and other non-native creatures have moved in.

As the warming trend continues, experts say some marine species will thrive as others struggle to survive in the face of temperature, environment and predator and prey changes.

“It’s not all bad news, and it’s not all good news,” said Jon Hare, science and research director for the National Oceanic and Atmospheric Administration’s Northeast Fisheries Science Center. “There are both winners and losers in this situation.”

Although many Chesapeake Bay creatures could be negatively affected, there’s at least one creature that experts believe could adapt: Virginia’s trademark blue crab. The species is well-equipped to deal with warming water temperatures and changes in its habitat, experts say.

“We are cautiously optimistic that the crab population will do well,” Lipcius said.

The blue crab Callinectes sapidus. (Courtesy VIMS, © S. Salpukas/W&M.)
The blue crab Callinectes sapidus. (Courtesy VIMS, S. Salpukas/W&M)

Fisheries management

In a region where commercial fishing dominates both culture and industry, changes in the Bay’s marine life in the Chesapeake Bay is also likely to be felt by watermen.

Virginia’s fishermen landed $168 million in 2014 from fishing and catching shellfish in the Bay, according to 2014 commercial fisheries industry data from the NOAA, the most recent data available.

As populations of shellfish and finned fish increase or decrease, catch limits will also likely need to be changed from their current regulations, Hare said, who researches fisheries along the Northeast Continental Shelf for the NOAA, extending from Cape Hatteras, N.C. to the Gulf of Maine, outside of the Chesapeake Bay.

According to Hare, each state has a fixed percentage of certain sea creature populations they can harvest each year, which is governed along the East Coast by the Atlantic States Marine Fisheries Commission, the Mid-Atlantic Fishery Management Council and the New England Fishery Management Council.

Species gravitating north has sparked some conflicts as populations increase, but fishing limits remain the same.

“For example, management of black sea bass along the Atlantic Coast is still based upon the [species’] distribution of the late 80s and 90s,” he said.

The three fishery management agencies have turned their attention to the changing populations along the East Coast, and are now working to adjust regulations. The Atlantic States Marine Fisheries Commission will have a four-hour “climate change working group” Jan. 30 in Alexandria, Va., according to the organization’s website.

“It’s very much a present-moment conversation that’s happening,” Hare said. “These agencies recognize things are changing and are working on how to address them.”

Science behind the changes

Data from the NOAA shows the average temperature of the earth has been gradually warming since the early 1970’s, after a rapid temperature drop through the 1960’s.

A warming trend in the air, evidenced by NOAA data over the years, translates to warmer ocean waters as well, according to VIMS News & Media Director David Malmquist.

Sea surface temperatures were the warmest on record in 2012, followed by slightly lower temperatures in 2013-2014, but temperatures still remain well above average, according to the NOAA. 2016 was hottest year recorded in the past 137 years, and was also the third consecutive year a new global annual temperature record has been set, according to the NOAA.

global_land_and_ocean_temps,_NOAA
(Courtesy NOAA)

A study by the University of Maryland Center for Environmental Science also shows warming water temperatures recorded in more than 92 percent of the Bay’s waters. Another study by the U.S. Geological Survey found an overall increase of 1.98 degrees Fahrenheit in air temperatures and 2.52 degrees in stream temperatures in the Chesapeake Bay region from 1960 to 2010.

Although scientists expect 2017 might be cooler, because 2016 was an El Niño year — meaning sea surface temperatures rose across the central and east-central Equatorial Pacific — Malmquist said the general warming trend is still an issue.

Heat from the ocean transfers into the air, Malmquist explained, meaning the air temperature can change from year to year, while the entire earth, both land and sea, is still getting warmer.

“A really important thing to think about is that NOAA is typically talking about air temperature,” Malmquist said. “Their system thermometers recorded the highest year ever in 2016, but the vast majority of the heat in the Earth’s system is in the ocean, not the air. 2017 might be cooler in the air, but if you were to look at the entire Earth system, including both the air and the water, it almost certainly would be warmer.”

Less than a three degree Fahrenheit increase over 30 years might not feel much different for humans, it has a strong impact on marine creatures, Lipcius said.

Keeping the blue crab

There is good news for Virginia’s crab enthusiasts: Blue crab, known for their adaptability, may endure the Chesapeake’s warming temperatures.

Winter blue crab dredge survey results show the blue crab population has ebbed and flowed since the early 1990’s, but Lipcius believes the crab population will likely endure habitat changes due to warming water temperatures.

Buckroe Beach in Hampton, Va., Jan. 25, 2017. (Sarah Fearing/WYDaily)
In a region where commercial fishing dominates both culture and industry, changes in the Bay’s marine life in the Chesapeake Bay is also likely to be felt by watermen. (Sarah Fearing/WYDaily)

“I think ultimately my opinion would be that the blue crab is going to continue to do well as long as it’s not over-fished,” he said. “It may even increase some. It’s probably one of the more stable species in the Bay because they’re so adaptable.”

The blue crab physiology is fundamentally tropical, meaning the crabs have adapted to warm waters. Blue crabs are also found in the Gulf of Mexico, Lipcius said.

“These crabs are very well adapted to the warming conditions,” he added. “In the Chesapeake, females are not having two to three broods per year. In the near future, they might produce three or four broods.”

Diminishing amounts of seagrass in the Chesapeake may also be a non-issue for blue crab populations, as the crabs are “supremely adapted” to variation and changing conditions, Lipcius said. New blooms of red algae, scientifically known as gracilaria, in the Bay have begun to provide a habitat alternative for blue crabs.

Red algae is an exotic species that colonized the bay 10 to 15 years ago, and has expanded into some areas where eelgrass has disappeared, Lipcius said.

“We probably are going to lose eelgrass at some point, at least in the lower Bay,” he said. “But now they will have gracilaria instead. … On the habitat side, blue crabs will probably do well.”

Moving north

One of the biggest concerns with warming waters is declining habitat suitability for organisms that live in the Chesapeake Bay, forcing them to move north.

“Some things are leaving and moving north to cooler waters, and other things are coming in from the south,” said Carl Hershner, director of the Center for Coastal Resources Management at VIMS.

(Courtesy NOAA)
Change in temperature within the Tidewater Region from 1950 to 2016. (Courtesy NOAA)

There have been a number of species, including blue crab, scup and black sea bass, that have shifted or extended northward along the Atlantic coast, said Hare.

“The list of species is quite long,” Hare said.

Blue crab have been found as far north as the Gulf of Maine in recent years. Although the blue crab are simply expanding north, and not actually shifting from their location from the Chesapeake Bay, warming waters in the north are allowing them to survive further up the East Coast. Due to their adaptability as a tropical species, and their ability to survive on many different food sources — including feasting on their own species — the crabs are likely to remain in the Chesapeake, Lipcius said.

“There are actually new fisheries for blue crab popping up on Long Island, New York, and some blue crab have been spotted in Maine,” Lipcius said.

Hare, who co-authored a research publication on the changing spatial distribution of fish due to changes in climate and population size, said some species on the East Coast have moved between 40 and 200 kilometers north over the past 40 years.

There are always exceptions to the trends scientists see, however.

“The other interesting piece about this is that, yes, in general species are moving northward, but that’s a generality, and there are exceptions,” Hare said. “Some species [such as little skate] are moving south, and it’s not clear why. It’s something scientists are working to understand”

Losing habitats

Eelgrass, the preferred habitat for blue crabs and other species, is one plant species that has, at least in part, been affected by warming waters in the Bay, Hershner said.

The eelgrass losses have been particularly dramatic in Virginia, he said. Since the 1950s, there has been a large decline in seagrass due to degraded water quality, according to VIMS.

Eelgrass meadow with numerous reproductive shoots. (Courtesy VIMS, © E. Shields/VIMS)
Eelgrass meadow with numerous reproductive shoots. (Courtesy VIMS, © E. Shields/VIMS)

At its peak, the Bay may have supported more than 600,000 acres of submerged aquatic vegetation, including close to 200,000 acres of seagrass in the 1930s, according to VIMS. In 2015, only 92,315 acres of submerged aquatic vegetation, or seagrass, were mapped in the Chesapeake Bay and its tributaries, a 53.8% loss over about 80 years.

Changes in climate and rising water temperatures create a stratification in the ocean waters, meaning the water closer to the surface mixes less with the colder, denser waters closer to the ocean floor. When the water doesn’t mix, the deeper, cooler water becomes less oxygenated, Hershner explained.

The stratification means the habitat for marine life, including fish such as striped bass and other plants, shrinks.

“What we know is that the habitat preference for striped bass is cooler, more oxygenated water,” he said. “The result of warming temperatures, among the results, is habitat squeeze, particularly during the summer.”

Mobile organisms will simply move to a more suitable environment, but immobile ones, such as plants, may simply disappear, Hershner said.

“Eelgrass is really valued as habitat for juvenile blue crabs and bay scallops,” he said. “They love eelgrass because of its protection from predators. That’s where you could find lots of baby crabs, but as we lost the eelgrass, we lost the bay scallops. The crabs just moved elsewhere.”

Prey and predators

While blue crab are well-equipped to deal with temperature and habitat changes in the Chesapeake, Lipcius believes incoming predators from warmer waters may pose a threat.

“Some species are extending northwards and changing the predator and prey interactions in any given system,” Hare said. “There are predators in a new area where they didn’t occur previously.”

Changing water temperatures can affect the dynamics of an ecosystem: As some species move away from their native waters, other species – both predators and prey – move in.

Some native species, such as blue crab, may successfully cope with warmer water temperatures, but new creatures in the waters are likely to alter the predator-prey balance interactions, Hare said.

Blue crabs may be adaptable to warmer temperatures, but one concern is the changing food web, the interconnected chains of what-eats-what, as new predators and prey move into the region.

Red drum fish, sea turtles and diamondback terrapins are known predators of blue crab, and may be more active in the Chesapeake Bay as water temperatures increase, Lipcius said.

“The dicey situation is with the food web, and what kind of changes we will see there,” he said. “What’s going to happen with the crabs’ main predators? Are they going to become more prevalent, or not?”

Fearing can be reached at 207-975-5459.