City at the Water's Edge: A Natural History of New York

Chapter 6: Muddied Waters

6 M u d d i e d W a t e r s Looking across the salt marsh of Jamaica Bay, I see the skyscrapers of Manhattan shimmering in the distance, their hard geometry juxtaposed against the soft muddy lines of tidal flats and wavy grasses. The city seems a world away, and a time apart. Dwarfing the Manhattan skyline, a snowy egret stalks its prey at the edge of the marsh, its head cocked, motionless. Here, a bird in the marsh reenacts an ancient scene; there, manmade towers rise like upstarts— hives of concrete and glass that serve as a human habitat. Before cities were dreamed of, the New York archipelago was created when the last glacier receded, and a rising sea reclaimed the continental shelf. In the glacier’s wake, the land slowly rebounded from the weight of the ice, and islands rose from the sea. Over the millennia, the ocean continued to encroach on the land, drowning the mouths of rivers like the Hudson, Connecticut , and Hackensack. The commingling of fresh and salt waters created estuaries, which are tidal rivers—geologically rare ecosystems that form only when sea level reaches a certain point. At high tide, the sea pushes upriver, and at low tide, the sea withdraws—hence the Lenape name given to the Lower Hudson, Mahicanituk, which eighteenth-century Mahican scholar Hendrick Apaumaut translated as “the great waters or sea, which are constantly in motion, either ebbing or flowing.”1 The word “estuary” is derived from the Latin word aestus, meaning tide. In the shallow waters of the estuaries , sediments eroded by tidal action are deposited along the shores, building mudflats where cordgrasses take root and grow into salt marshes. The estuaries, bays, and salt marshes of the New York City region have supported a diversity of species, including our own: hunter-gatherers settled along the waterways here, thriving for thousands of years on the abundance of plants and animals that shared their habitat, and gave them the food, shelter, fuel, clothing, and tools they needed.2 Hudson River historian Robert Boyle describes the Lower Hudson estuary as “a nutrient trap, a protein plant, a self-perpetuating fertilizer factory” fed by an array of minerals eroded from the land, enriched by the recycled remains of dead plants and animals, and stirred by tidal action. The brackish waters are inhabited by both fresh- and saltwater species of fish, including striped bass, alewives, and shad that swim upriver every spring to spawn; weakfish (sea trout) that spawn in the estuaries; summer flounders (fluke), and bluefish larvae and juveniles that feed in the estuaries in the summer months. Some shellfish—oyster, crab, and clam—spend their whole life cycles in the estuarine ecosystem, while others such as shrimp feed in estuaries during their larval stage.3 The salt marshes fringing the shores harbor a diversity of species. Blue crabs molt in the protected waters of salt marsh creeks, and the larvae of crustaceans and mollusks drift on their surface. Along creek banks, fiddler crabs burrow, excavating pellets of sand or mud with their super-sized claws. Little white marsh periwinkles graze on the algae that coats the lower stems of cordgrass , while fish such as menhaden and mullet forage on the decaying stalks. Salt marsh amphipods, tiny shrimplike creatures, emerge at night during low tide, scavenging for decayed plant and animal food; before daylight, they excavate little underground chambers above the high tide line, where they rest by day safe from feeding shorebirds. A host of insect species inhabit the marsh, including dragonflies, beetles, and a number of biting flies, much to the misery of those mammals whose blood females feed on. Throughout the salt marsh in summer months, the ubiquitous golden saltmarsh mosquito abounds, spending its larval stages in the shallow waters. Minnows—mummichog, killifish , stickleback, and sheepshead—feed on the abundant mosquito larvae.4 Intertidal sand and mud flats are inhabited by numerous tube-building worms and other burrowers. The ice cream cone worm (once called the trumpet worm, so-named because the wide end of the tube is flared) is one of the most skilled builders. It uses its feeding tentacles to carefully select sand grains of the same size, secreting mucous to cement the grains into a delicate cone house. At low tide you might see the tip of the inverted cone protruding above the wet sand or mud. The worm’s pinkish body is splotched with blue and red, and its head sports...