1117 GMT November 12, 2019
In a warmer Chesapeake Bay in the US, for instance, oysters, mussels and clams could struggle as a hike in acidity from carbon dioxide absorbed from the atmosphere causes their shells to grow more brittle, pilotonline.com wrote.
But there’s one keystone species that might actually thrive in the projected new environment: Blue crabs.
Researchers at the Virginia Institute of Marine Science in Gloucester Point and at the Chesapeake Biological Laboratory (CBL) in Maryland are finding that blue crabs not only could grow bigger in a warmer bay, they could become active year-round, rather than burrow into the bottom sediment to overwinter.
They’re also discovering that, unlike with bivalves, greater acidity doesn’t seem to weaken crab shells.
The findings caught some researchers off-guard.
“I was surprised,” said Thomas Miller, director of the CBL at the University of Maryland Center for Environmental Science.
“I think it’s one of those cases where, after the fact, you can sort of rationalize the results, but they certainly weren’t the results that you were expecting.”
At Virginia Institute of Marine Science (VIMS), biological scientist Rochelle Seitz said she wasn’t surprised by Miller’s results, “but we did think there would be some negative effects. And there still may be some negative effects of the acidity on things like behavioral responses of blue crabs.”
The CBL research, conducted over several years by then-doctoral candidate Hillary Lane Glandon, focused on the effects of increasing water temperatures and acidity.
At VIMS, graduate student Katherine Longmire is looking at the effects of increased acidity and lower salinity on blue crabs and hard clams. VIMS is affiliated with the College of William and Mary in Williamsburg.
Both laboratories placed a large number of crabs in individual tanks and exposed them to various conditions projected for the bay in coming decades because of climate change.
It’s long understood that the crab is responsive to temperature changes — that’s why it digs in for the winter when the bay turns cold.
Experienced bay watermen know that blue crabs don’t always bed down during a particularly mild winter, said Miller, but often can be spotted lumbering along the bottom.
And as you head farther south, crabs might not bed down at all, but keep on molting and growing all year, every year.
“It’s a gradient,” said Miller. “And I expect you’ll find the same thing with us — that, as the bay warms, you’ll find an increasing number of years in which crabs do not overwinter.”
It’s their ability to molt that likely protects crabs from the corrosive effects of acidity.
Bivalves build hard shells using the compound calcium carbonate, which is weakened by acidic waters.
A blue crab also builds its hard carapace of calcium carbonate, but it’s a much more complex structure that incorporates ‘islands’ of magnesium, enabling it to be more soluble and metabolically active for molting.
“A crab maintains a lot of energetic physiological control over the shell itself, and so it’s resistant to the acidification,” said Miller.
Some studies indicate that blue crab shells may actually strengthen under low pH or acidic conditions, said Seitz.
Longmire and other students at VIMS are using a ‘pinch-o-meter’ to try to gauge claw strength in crabs exposed to higher acidity and lower salinity.
While findings suggested blue crabs can adapt swimmingly to a changing bay, it’s also known that altering their environment can stress them out and affect their ability to feed.
So, as the bay changes, said Seitz, “we don’t know whether the predator-prey interaction is going to be stronger or weaker.”
Already, the ranges of various marine species are shifting. Some species that once were rather foreign to Virginia shores are starting to show up, said Miller, while others could begin to shift out.
Soft-shell clams, for instance, are at the southern limit of their range in the bay and might shift farther north as temperatures warm.
That would deprive blue crabs of one of their main food sources.
But blue crabs are resilient and opportunistic in their eating habits and, as they slowly shift to become year-round predators, could adapt.
“There may be other warm-water species that invade the bay,” said Seitz.
“That are additional food sources for blue crabs, that actually enhance their prey base.
“Those are some of the things that we’ll just have to wait and see what the overall ecosystem changes are going to be.”
“I think climate change is the predominant issue facing our society,” said Miller. “And I think because of that we need to take it seriously.
“Our children will experience a different Chesapeake Bay than we have experienced.”