A cleaner bay, warmer temperatures and milder weather combined to fuel a surge in underwater grasses in the Chesapeake Bay to levels researchers haven’t seen in three decades.
Total bay grass abundance grew 21 percent from 2014 to 2015 — from 75,835 acres to 91,621, according to the Virginia Institute of Marine Science, which leads an aerial survey of grass beds every year.
That figure puts the bay just under half the restoration goal of 185,000 acres set by the Chesapeake Bay Program, a regional partnership for restoration.
Experts say it shows that efforts by Virginia and other bay states to clean up the polluted estuary are working.
“Clearly, we are on the right path,” CBP Director Nick DiPasquale said in a statement announcing the survey results. “And, just as clearly, we must continue our efforts if we are to succeed.”
The lion’s share of that increase is in widgeon grass, typically found in the moderately salty mid-bay, but increasingly showing up in new areas during the last three years, Robert “J.J.” Orth said in an interview Friday. Orth is head of the Seagrass Monitoring and Restoration Program at VIMS, an affiliate of the College of William and Mary in Williamsburg.
“We’re not sure if this is all tied to the climate-change issue, because the bay is getting warmer,” Orth said. Widgeon grass prefers hot, shallow areas, he said, “and it’s been growing in places that we’ve never seen in 30-plus years that we’ve been monitoring.”
In the freshwater areas of the upper bay and its tributaries, species such as wild celery also expanded their range.
In the salty lower bay, native eelgrass increased, but only by modest amounts. Eelgrass prefers cooler waters and is already on the southern edge of its range.
“So when we get these really hot summers as we had in (recent) years,” Orth said, “it dies back. And it dies back to where sometimes recovery takes a while.”
Climate change, then, helps some species, he said, but for the dominant grass species of the lower bay, “it doesn’t bode well.”
On the other hand, he said, for bay creatures that depend on underwater grasses for habitat or protection from predators — such as the iconic Chesapeake blue crab — there’s still reason for cautious optimism: Widgeon grass serves basically the same function as eelgrass for blue crab. So, if it continues to expand, it could make up for the loss.
“It could be a wash,” Orth said. “At least for blue crabs.”
One concern, though, is that widgeon grass is considered a “boom or bust” species that can change rapidly from year to year. Marine researchers aren’t sure what drives either extreme.
“There’s no rhyme or reason why we see some of these massive busts,” Orth said.
Still, said Brooke Landry, a biologist with the Maryland Department of Natural Resources, “I think we can take heart in the fact that it boomed last summer.”
“Be it freshwater wild celery or mid-bay widgeon grass,” Landry said, “submerged aquatic vegetation would not expand so rapidly and into areas where it hasn’t been mapped before if water quality wasn’t improving.”
In 2010, the U.S. Environmental Protection Agency directed bay states and the District of Columbia to begin installing pollution-control measures to reduce the amount of nitrogen, phosphorus and sediment dumped into the 64,000-square-mile watershed and, ultimately, the bay.
Farms and wastewater treatment plants are the biggest sources of nitrogen and phosphorus, which cause massive algal blooms, red tides and dead zones in the bay.
Agriculture and development are major contributors to erosion and the sediment that blankets important hard-bottom habitat and clouds the water column, keeping sunlight from reaching underwater grasses.
Severe storms early in the growing season also can dump large amounts of sediment in the bay, burying young plants.
VIMS conducts its aerial survey from mid-May to late September, Orth said, starting in the lower bay and working its way up to catch blooms at their peak.
The survey breaks the bay down into four salinity zones that reflect different grass species that respond differently to growing conditions.
From 2014-2015, the survey found:
*Fresh waters: Grass abundance up 1,959 acres to 17,454 acres, or 85 percent of the zone goal;
*Slightly salty waters: Up 2,681 acres to 9,881 acres, or 96 percent of the goal.
*Moderately salty waters: Up 10,680 acres to 47,728 acres, or 40 percent of the goal; and
*Very salty waters: Up 862 acres to 16,558 acres, or 49 percent of the goal.
The total restoration goal of 185,000 acres was set based on the “single best year” for underwater grasses, said Orth. Those years stretch back to the 1950s and 1960s.
“If we reached that, that would be phenomenal,” Orth said. “And I would like to think that maybe we would see that, in at least my lifetime.”
Dietrich can be reached by phone at 757-247-7892.
