Underwater grasses rebounded last year in the Chesapeake Bay and its rivers, partially reversing a three-year decline in a key indicator of the bay's health, scientists said Monday.
Aerial surveys detected a 24 percent increase in aquatic vegetation baywide, from 48,195 acres in 2012 to 59,927 acres last year. That's only about third of the goal federal and state officials have set for restoring grasses to levels approaching what they were 50 or 60 years ago.
Robert J. Orth, a biologist with the Virginia Institute of Marine Science who coordinates the two-state survey, called last year's growth "a good recovery from what we've been seeing in the previous three years, but it still is far off from our high point" of nearly 90,000 acres in 2002.
Scientists track bay grasses annually because they are vital habitat for crabs, fish and waterfowl. They're also sensitive to changes in water quality, which Orth said makes them useful for monitoring the bay's condition.
Before last year, the bay's grasses had declined to a level not seen since 1986, a retreat that scientists attributed to a spate of extremely hot summers and severe storms, as well as a troubling decline in overall water clarity. Like land-based plants, underwater grasses need sunlight to grow.
Orth and Lee Karrh, a biologist with the Maryland Department of Natural Resources, said last year's improvement likely stemmed from more favorable weather conditions. The healthiest growth occurred in the upper and middle portions, with the Susquehanna Flats regaining some of the lushness they lost after Tropical Storms Irene and Lee in late summer 2012.
Widgeon grass accounted for nearly all the rebound seen in the midbay, from just south of Cambridge down to the Pocomoke River, which Orth described as a mixed blessing. It's prone to rapid proliferation followed by steep declines, he said, so it may be vulnerable to storms. In years past, he noted, the bay supported a greater variety of grasses, capable of coping with varying conditions.
Despite gains virtually everywhere else, Orth said grasses dwindled in the Severn, South and Patuxent, and virtually disappeared from the Magothy in northern Anne Arundel County. He attributed most of those losses to lack of water clarity but said he was unsure of the cause in the upper Patuxent.