"Feller hasn't run ashore, he don't much know this Bay," a waterman once said to me after he pulled my ketch off a tenacious sandbar. It was the nicest thing anyone could possibly say under such embarrassing circumstances and it made me feel much better. What he meant, of course, is that the Chesapeake does not lack for the shallow water that is another prime estuarine requirement. The average depth of the Chesapeake, mother river and tributary channels included, is twenty-one feet. For most of the Bay, fifteen feet or less would be a better figure.
Shallower still are the vast areas along the Eastern Shore, the waters surrounding the great marsh islands of Tangier Sound, for example, which Captain John Smith called the Isles of Limbo, where vigorous sounding will fail to uncover anything deeper than five feet. Captain Smith was glad when he left, and today's less venturesome sailors shun the marshy islands like the plague. Yet these very shoal waters have their place, if not for yachtsmen. They provide an optimum habitat for such rooted aquatic plants as wild celery and widgeongrass, the choice of waterfowl, or eelgrass and sea lettuce, which although acceptable to ducks and geese, are only preferred by small fish, crabs and young seed oysters. Almost invariably the shoals supporting these water plants are bordered by marsh. The marshlands in turn support a much greater growth of plants, plants which want to have their roots covered by water some of the time, but which cannot tolerate it all of the time. Dominating these, heavily outweighing all other species in sheer tonnage and outdistancing them in distribution, are the the spiky Spartinas or cord-grasses. Spartina patens that is, which ripples in windrows or lies in natural cowlicks on the firmer ground, and Spartina alterniflora, taller and denser, which grows on the quaking mudbanks and along creek borders first invaded by tidewater.
The interaction between the two plant communities, one just below the water and the other barely above, is admirable. The marsh grasses are the storehouse or granary. The agents that mill them and their associated plant and animal life, principally algae and insects, are death and decay. We cannot readily see the crop so produced, since it ultimately takes the form of pinhead particles of detritus and bacteria-manufactured nutrients dissolved in the water, but it beggars anything that happens on dry land. Most of the Chesapeake's marshlands produce an annual average yield of five tons of vegetation per acre. Those in the southern reaches, along the lower Eastern Shore, go as high as ten. Down every tidal gut and through every big "thorofare" and little "swash" or "drain," as the breaks in the marsh islands are called, there comes an enormous and nourishing flow of silage made from this decomposing Spartina crop. Waiting to receive the flow, well protected by wavy forests of eelgrass, are many forms of life. First recipients are plankton and the larvae and young of larger forms, who need it most. In the later category are enormous infant populations of fish, clams, oysters, jellyfish and worms. Predominant among adult forms are the blue crabs, who have a fine time of it preying on the small fry, including, sometimes, some of their own.
The animals of the aquatic plant communities give something back to the marsh in return, although not as much as they receive. Since they consume great quantities of marsh-produced nutrients, they also therefore release considerable amounts of nitrogen and phosphorous after their rapid browse-feeding and digestion. The waters so fertilized return to the marshes twice every twenty-four hours, as sure as the moon and sun make tides. The same waters of course, also bring salt, which is what permits the cortdgrasses to reign as uncontested monarchs of the marshland. Alone in the plant kingdom, the Spartinas thrive on it. Or, more accurately, despite it. Thus interaction.