Underwater grasses in the Chesapeake Bay declined more than 20 percent last year, hurt by summer heat and heavy rains and snow melt that sent tons of mud and debris into the bay, the Chesapeake Bay Program said Wednesday.
The losses mean levels of the grasses that provide food and homes for fish, birds and other species have dropped to their lowest point since 2006. Scientists said grasses are now at historically low levels, but the news was tempered by growth found in some parts of the bay.
The underwater grasses are important to the health of the Chesapeake because in addition to providing habitat for crabs and striped bass, they also improve water clarity by trapping sediment, add oxygen to bay water, provide food for waterfowl and help prevent shoreline erosion.
Heavy rains from back-to-back storms that caused widespread flooding throughout the Northeast last fall sent tons of garbage and sediment into the bay. That raised concerns about damage to underwater grasses in the upper bay, but the Chesapeake Bay Program said last year that aerial photos taken in November showed the damage was not as bad as feared.
The annual survey released by the program run by the federal Environmental Protection Agency showed grass beds throughout the bay declined from 79,664 acres in 2010 to an estimated 63,074 acres in 2011.
Bob Orth of the Virginia Institute of Marine Science, the coordinator of the annual survey, said summer heat also caused eelgrass beds in the lower bay to decline. The wet spring and fall, meanwhile, hurt the grass beds at the mouth of the Susquehanna River at the northern end of the bay. However, the main portion of that area, known as the Susquehanna Flats, which had tripled in size since 1991, remained intact. That shows how resilient grass beds can be, Orth said.
“The upper bay was essentially a total mud bank for almost two months,” Orth said.
That changed normal growth patterns. Lee Karrh, who chairs the program’s Submerged Aquatic Vegetation Workgroup, said brackish parts of the middle bay saw dramatic increases after years of losses. Lower salinity from the heavy rains is thought to have stimulated dormant seeds of grass species in the middle bay.
The survey, for example, found the first bed of freshwater grasses in the main portion of Virginia’s James River since the area was first surveyed 1998.
What will happen this year following an extremely warm winter with little rain or snow is not clear, the scientists said.
While pollution reductions have helped grasses rebound in the upper bay and withstand last year’s heavy rains, Orth said problems with water clarity in the lower bay have left the grasses in shallower water where they are more susceptible to warmer temperatures recorded in recent years.
“We are very, very concerned about the long-term survivability” of those grasses, Orth said.