Underwater grass beds expanded by nearly 18 percent in the Chesapeake and its tidal tributaries last year, driven largely by a burst of widgeon grass in the middle and lower sections of the Bay.
But the annual Baywide aerial survey also showed a continued expansion of the Susquehanna Flats, the largest grass bed in the Chesapeake, which now covers more than 15,000 acres.
"The success story continues at the Susquehanna Flats," said Bob Orth, a scientist with the Virginia Institute of Marine Science who oversees the annual Baywide survey. "But you still have to look at the big picture. There are still areas of the Bay that are not doing very well."
Baywide, grasses covered 76,861 acres in 2008, up from 64,917 acres in 2007. That achieved 42 percent of the Bay Program's underwater grass restoration goal of 185,000 acres, up from 35 percent last year.
Widgeon grass accounted for about three-fifths of the Baywide increase of 11,944 acres. Widgeon grass, which dominates the middle section of the Chesapeake, is notorious for expanding rapidly when conditions are good, but disappearing just as rapidly when water quality is poor.
"In one year, it can be everywhere, and the next year be completely absent," Orth said.
The annual aerial survey is a closely watched indicator of the Bay's health. Grass beds require clear water to absorb the sunlight they need to survive, so they are very susceptible to nutrient pollution, which spurs algae blooms, and sediment runoff, which clouds the water.
They also provide some of the most important habitat in the Chesapeake, providing shelter for juvenile crabs and small fish, and food for waterfowl.
"They are the sentinels of the Bay," Orth said. "They tell us what is going on."
Last year, grasses increased in all three geographic regions, the Upper, Middle and Lower Bay, for the first time since 2001:
- The Upper Bay, which stretches from the Chester and Magothy rivers north, increased 21 percent, from 18,922 acres in 2007 to 22,954 acres in 2008. Most of that was in the Susquehanna Flats. The Bay Program goal for that region is 23,630 acres.
- The Middle Bay, which stretches from the Chester-Magothy line south to the Pocomoke and Rappahannock rivers, increased 15 percent, from 29,992 acres in 2007 to 34,521 acres in 2008. The Bay Program goal for that region is 115,229 acres.
- The Lower Bay, which stretches from the Pocomoke-Rappahannock line south to the mouth of the Chesapeake, increased 21 percent, from 16,004 acres in 2007 to 19,386 acres in 2008. The Bay program goal for the lower Bay is 46,030 acres.
The Baywide and regional goals were determined by examining historical aerial photos of the Bay and identifying the maximum amount of grass that was present in each segment of the Bay in any given year.
Orth said the beds on the Susquehanna Flats, which increased by about 2,500 acres in 2008, now slightly surpass the "best year" previously observed. "We could be approaching levels like the old timers actually saw," he said.
Biologists would like to see more beds like the Susquehanna Flats. The area, once important for waterfowl, was left barren after Hurricane Agnes hit in 1972, leaving the beds buried under sediment that was washed into the Bay.
About a decade ago, the grasses began coming back, and the bed has expanded ever since. "It's like the Energizer bunny," Orth said. "It keeps on going and going and going."
It serves as a seed source for other areas-many of the nearby rivers have surging grass beds, thanks to the Susquehanna Flats.
Today, the bed is so large it can withstand severe storms that leave other beds smothered in sediment or clouded by algae. Large grass beds modify their own environment by filtering the water, essentially maintaining their own water quality.
That gives scientists hope for other areas. "The Upper Bay continues to show that when you have a system coming back, and it can get enough of a toehold, it can really hang on when you get a couple of bad years," said Rich Batiuk, associate director for science with the EPA's Bay Program Office.
But not all areas of the Bay are faring so well. Despite the increase in acreage last year, the long-term trend is toward worsening water clarity in much of the Chesapeake.
"The eelgrass plants in the Bay are essentially telling us this," Orth said. "We have essentially lost all of the deep water eelgrass beds in the Bay in the last 10-15 years."
Two decades ago, he said, the average Secchi disk water clarity at 26 monitoring sites within the range of eelgrass in the Bay was 1.75 meters. Now, it is 1.25 meters. "In the last 20 years, we have lost half a meter of water clarity and we believe this may be the main reason we have lost almost all of the eelgrass beds in waters deeper than 1 meter," Orth said.
Eelgrass is a species of particular concern because it is the dominant species in the lower Bay, where it is especially important for juvenile blue crabs.
Over the past decade, the overall trend in the lower Bay, which is dominated by eelgrass, has been downward. That was exacerbated in 2005, when poor water clarity, combined with warm temperatures, caused a widespread eelgrass die-off.
Recent surveys have suggested that eelgrass appears to have grown back in many areas since 2005, but Orth said it was difficult to determine the extent of the eelgrass comeback last year because it was mixed with widgeon grass in many areas.
While scientists welcome the return of widgeon grass, bursts of growth in the past have often been followed by declines within a few years.
That instability is compounded because many of the beds in the Middle Bay consist only of widgeon grass today, whereas they had a broader mix of species in the past, which helped beds withstand adverse conditions.
"The Middle Bay doesn't have the diversity of plants that it used to have," Orth said. "There is a lot of widgeon grass, but that area used to have six or seven species. Now it has one."
The Honga River, Tangier and Smith island region, Eastern Lower Chesapeake Bay, and Mobjack Bay all had large expanses of widgeon grass last year.
Not all areas where widgeon grass is common improved. The Choptank and Little Choptank rivers continued to lose grass beds, a trend which has been going on for several years. Grass beds also declined in the lower Patuxent and lower Potomac rivers.
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.
For information about the aerial survey and survey results, go to www.vims.edu/bio/sav/.