The Chesapeake lost a quarter of its underwater grasses last year, with the Baywide acreage falling to its lowest level since 1989, according to figures from the latest annual survey.
The survey turned up some good news—the Susquehanna Flats, the largest bed in the Bay, remained intact despite a late June deluge that smothered much of the Bay with sediment.
But many other areas suffered extensive losses. Among the hardest hit were areas in high-salinity regions dominated by eelgrass, which suffered a massive die-off, apparently triggered by warm temperatures. Bay grasses in other areas were whipsawed between dry conditions in the spring and near-record river flows from a long rainy stretch in June.
“The fact is, last year was a year in which a lot of plants just didn’t make it,” said Bob Orth, a seagrass expert at the Virginia Institute of Marine Science who conducts an annual aerial survey of the Bay’s grass beds.
Overall, the survey counted just 59,090 acres of grasses, down from 78,263 acres in 2005, That’s just a third of the Bay Program’s restoration goal of 185,000 acres.
Results by region show:
- The Upper Bay, from the Susquehanna River south to the Chester and Magothy rivers, decreased from 19,464 acres to 15,510 acres last year, a decline of 20 percent.
- The Middle Bay, from the Bay Bridge south to the Rappahannock River, decreased from 39,575 acres to 30,659, a decrease of 23 percent.
- The Lower Bay, from the Rappahannock River and Pocomoke Sound south to the Bay’s mouth, decreased from 19,220 to 12,922 acres, falling 33 percent.
“It was devastating. I couldn’t believe how bad it was,” said Bill Dennison, a scientist with the University of Maryland Center for Environmental Science. “It was the worst water clarity year ever measured. After that June rain, it was chocolate out there, and it never cleared up.”
The annual survey is a closely watched indicator of the Bay’s health. Grass beds require clear water in order to absorb the sunlight they need to survive, so they are very susceptible to nutrient pollution, which spurs algae blooms, and sediment in runoff.
Although losses were observed throughout the Bay, the eelgrass declines in the lower Bay were especially troublesome. Eelgrass is the only underwater grass that will survive in many high- salinity areas of the Chesapeake. If it fails to bounce back, huge areas would be left without a critical habitat for fish and shellfish. Eelgrass in the lower Bay is considered especially important for juvenile blue crabs, which use the dense beds as cover from predators.
Orth said small patches of eelgrass—less than a square foot—are too small to be seen by the aerial photography, but remain in many areas. Seeds from those plants could form the basis of a recovery, if they survive. “As long as the beds are not impacted by a really hot summer, as long as we don’t have a hurricane, then I think we will be OK in 2007,” he said.
In contrast to the Lower Bay, where grass acreage has been declining for a decade, the amount of grasses in the Upper Bay remains high, despite last year’s setback, compared with a decade ago. Unlike the Lower Bay, which is dependent on eelgrass, a number of freshwater species thrive in the Upper Bay; in recent years, seeds and plant fragments from those beds have shown a remarkable ability to rebound from adverse events.
“I’m still pretty encouraged about what we’re seeing in the Upper Bay, and expect we’re going to see something like a full recovery this summer, unless we have some type of terrible weather event,” said Mike Naylor, a biologist with the Maryland Department of Natural Resources.
He also said some grass beds, obscured by murky water during the aerial survey, appear to have survived. “In some of those areas, we didn’t notice any declines,” Naylor said.
Also, the huge grass bed on the Susquehanna Flats remained unscathed during last year’s poor conditions—confirming the long-held contention of scientists that large beds can influence their own environment and withstand severe events if they become large enough.
The small size of many other grass beds, scientists say, contribute to their instability.
Scientists say more than 200,000 acres of grass beds once covered the Chesapeake, providing huge amounts of habitat for an array of species. The amount began dropping in midcentury as sediment from the land and nutrient-spurred algae blooms began clouding the water.
Grasses bottomed out at an estimated 38,000 acres in 1984, and slowly increased until the 1990s. Their recent peak was 89,659 acres in 2002, after four years of drought sharply reduced the amount of nutrients and sediment in the water.
The annual Baywide grass estimate is derived from an analysis of more than 2,000 black-and-white aerial photographs taken between May and October.