Much more than hors d'oeuvres

THE BALTIMORE EVENING SUN

The Chesapeake Bay Foundation yesterday released "Turning the Tide: Saving the Chesapeake Bay." Written by Tom Horton and William M. Eichbaum, underwritten by the Abell Foundation and published by Island Press, the book amounts to a status report on the bay, with recommendations for rescuing the estuary from the human onslaught. This is the second of three excerpts. IT IS on the shallow bay bottom, along with the grass beds, that we find yet another regulatory system on the order of the forests, marshes and grasses. You may know this elegant mechanism of homeostasis as the old, gray oyster (variously rendered as "aryster," "oistuh," "erster" and "arschture."

The oyster is a good example of how we sometimes underestimate the importance of bay creatures by considering them mainly as they relate to our bellies and our commerce. For more than a century, dating from the 1860s, our huge harvests of the tasty bivalve were synony mous with Chesapeake Bay's incredible bounty.

In retrospect, the towering peaks of oyster production during the late 19th century were not sustainable. Rather, they simply represented a short-term mining of the wealth accrued on the bay's bottom. The edible oyster meat harvested in Maryland waters alone during the peak of that exploitation was equivalent to the yield from 160,000 head of prime steers. A testament to the resilience of the estuary and the oyster is that harvests could remain at world-class levels (1 to 3 million bushels a year) almost until the last decade of the 20th century. Overfishing, combined with diseases, mismanagement and pollution, has now reduced the oysters in the bay to an estimated 1 percent of their numbers before heavy harvesting began after the Civil War.

One percent! Think of that. And think of what it would be like to live in your house if you had sold off 99 percent of the plumbing, or 99 percent of the heating and air conditioning system, or 99 percent of the roof. Because in taking too many of the bay's oysters, we have been losing much more than a plentiful supply of appetizers or a significant portion of our seafood economy. We have been destroying a vital filter, a recycler, a habitat for other creatures and a banker of food energy like the underwater grasses.

After their free-floating larvae attach to other oyster shells and become spat in the first weeks of life, oysters never move. They have traditionally been superabundant in the bay because its vigorous circulation brings them plenty of food, and because their food is phytoplankton, which grows so well in the sunlit shallows. (The bulk of oysters grow in water 30 feet deep or less.) They are superb filterers, feeding by gaping their shells slightly and pumping bay water through their gills at rates up to 2 gallons per hour.

In addition to growing fat oysters, this process has at least two other important consequences for the estuary as a system. By sucking in sediment that clouds the bay's waters, and depositing it on the bay bottom as compacted fecal matter, the oyster clears the water, thereby helping sunlight penetrate and grow more plankton and more underwater grasses. One estimate is that the pre-1870 stocks of oysters in the bay had the potential to filter a volume equal to that of the entire Chesapeake every few days -- compared with a "filtration time" of nearly a year for today's diminished stocks.

Moreover the oyster, like the grasses, seems to have been a "banker" and recycler of the huge pulses of nutrients that surged off the watershed in the wet springtime. It filters the lush, nutrient-fertilized spring plankton bloom through its gills, using some of it for growth but also depositing nutrient-rich feces on the bay's bottom. On the bottom, which is never far from the top, these nutrient packages can be recycled into production again. But just as the bay's oysters no longer vacuum much sediment from the water, so has their capacity to bank and package food for recycling declined drastically. Estimates are that the pre-1870 oyster population could have removed 23 to 41 percent of the plankton blooms. Now they are thought to remove about 0.4 percent -- a drop of fiftyfold or more. Where does the unfiltered plankton go nowadays? It appears that it goes to the bottom, where its decomposition can intensify problems with low oxygen.

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The damage humans have done to the bay and its watershed is nothing short of staggering. And with more millions of people moving into the region, the odds may seem long against a major turnaround. Indeed, this book details many alarming trends. But reading all the reports in the world cannot give one a full sense of this marvelous, 64,000-square-mile creature called Chesapeake. The best way to start saving the bay is through contact with parts of its system, whether it be made with a fishing rod or binoculars, from a duck hunting blind or the ooze of its bottom squishing up through the bare toes. Sometimes it is best to quit analyzing the bay and just listen to what its creatures have to tell us.

It may seem surprising, given the reputation of estuaries for producing and attracting huge quantities of species, that not many kinds of creatures live in the bay. To be sure, many visit at times of the year, either descending from their upstream, freshwater habitats or moving in from the oceans to feed or spawn. But in terms of full-time residents, both freshwater systems and the oceans, though far less productive than estuaries, support many, many times more varieties of life.

This seeming paradox simply reflects the estuary's basic nature -- lots of food production on the one hand, but also tremendous variability in environmental conditions: salinity that can swing from oceanic to lakelike and back; temperatures in the shallow that may freeze to the bottom mud in winter and soar above 90 degree in summer; water quality in the rivers that can change with an overnight rainfall. As a bay scientist once summed it up: "The chow's great if you can stand the hassle."

And that is just the point, and maybe the bay's best hope for survival into the next century -- much of what has survived there is able to stand a lot of hassle, is adaptable, tough, resilient to its core. So it is that blue crabs, while they find salinities highly suitable around the middle of the bay, near Tangier and Smith islands, also flourish in the freshwater reaches of the bay's tributaries and the near-ocean of its mouth -- and do better than one might expect in grossly polluted sections like Baltimore's harbor and Norfolk's Elizabeth River.

Oysters, though they can't move away from pollution, are able to survive days, even weeks, of depressed oxygen in the water by clamping their shells shut and switching their entire metabolic process. If overharvesting of big oysters, which are mostly females, creates problems for reproduction, male oysters are able to change their sex as needed to compensate. Even in their current, depleted state, they are still capable in some years of excellent reproduction.

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In sum, although the bay we are trying to restore is, on the one hand, a crippled version of the original, healthy system, its primary inhabitants are anything but fragile and nothing if not adaptable to change. They are the opportunists, the plants and animals that are best able to rush in and colonize new habitats during the intervals -- brief in evolutionary time -- when fertile estuaries like the Chesapeake occur during the short warming spells between the long ice ages. If you have ever hooked a rockfish or a shad on a line and felt it tug for its freedom, or tried to pry apart an oyster's shells, or attempted to pick up a big feisty jimmy (male) crab, then you know -- the bay vigorously, vitally, desperately wants to live.

Given half a chance to survive, its inhabitants will not be shy grabbing it.

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