(truenature)

Even when eelgrass washes ashore, its leaves still enter the food chain as nourishment for a host of tiny marine organisms.

Photo by Jeff Foott/Bruce Coleman

An Underwater Ark

Largely unheralded but teeming with wildlife, eelgrass is the base of the food web in coastal waters. Now scientists are on a mission to unlock its secrets and protect this vital habitat before it's too late.

By Christopher Solomon

As the moon draws back the waters of Washington's Puget Sound, Charles Simenstad lowers a car battery into a garbage can, wedges the can into a duct-taped inner tube, and attaches a motor and hose. He wades into Hood Canal with this homemade vacuum cleaner, plants the nozzle atop a small patch of green, and begins to suction up a tiny piece of one of the most productive yet imperiled aquatic ecosystems on the planet.

Seawater spits into a sifting pan. Carl Young hunches over it like some misplaced prospector squinting for gold. "It's just crawling with critters," says Young, a graduate student in aquatic and fishery sciences at the University of Washington in Seattle. At first I see only drifting motes of sand.

Then I notice that the motes are ricocheting about; the "sand" is alive—and apparently not enjoying the rude marine census. "There's gonna be harpacticoid copepods in here," predicts Young,"“and amphipods, isopods"—naming several of the more than 190 invertebrates that live in the Pacific Northwest's unsung eelgrass meadows.

Amid the beach's exposed eelgrass, a red rock crab hunkers, and clams spout miniature geysers. A starfish clings to the leaves at the surf's edge and waves its arms, Shivalike. "I consider eelgrass the [shallow-water] equivalent of the tropical rainforest in terms of biodiversity," says Simenstad, an estuary ecologist and coastal-wetlands expert at the University of Washington, before he wades into the water to help Young capture the tiny organisms living on the blades of eelgrass. Today's Hood Canal outing is part of a larger research project that aims to determine how the canal's juvenile salmon interact with the eelgrass and how changes in the eelgrass meadows affect the salmon's food supply.

In addition to Hood Cana'ls federally threatened summer-run chum salmon, more than 70 different fish in the Northwest's waters—from herring to buffalo sculpin—rely on eelgrass for habitat or nourishment. Its leaves calm waves and create a still place for animals to feed, hide, and lay their eggs. Its roots anchor sediments, which helps prevent near-shore erosion. An eelgrass sward is an apartment complex, a nursery for threatened species, a cafeteria, and a grand mulch-making machine that supports an entire web of marine life in shallow waters off the coast. It is, say scientists, the ecological linchpin of these areas.

It's no wonder, then, that many worry about the impacts of the plant's decline worldwide. Eelgrass is just one of 50 to 60 species of seagrasses found around the world. In a 1995 survey, researchers at the University of Washington and the University of New Hampshire estimated that 222,000 acres of seagrass had been lost in the previous decade. Estimates in the recently published World Atlas of Seagrasses put the worldwide extent of seagrass at about 44 million acres. But since much of the world’s supply hasn't been mapped, the true total, as well as how much has been lost, could be double that, says Fred Short, an oceanographer at the University of New Hampshire and one of the atlas's editors. Sandy Wyllie-Echeverria, a seagrass expert at the University of Washington's School of Marine Affairs and a coauthor of the 1995 survey, believes that sewage, dredging, and on-land development that flushes silt into the water are prime culprits. "The actual area lost is certainly greater," she says.

Eelgrass, officially zostera marina, grows in the shallows from Spain to Iceland, off Japan, and along the eastern and western coasts of North America. In Washington, where eelgrass's role as critical salmon habitat has linked it to the high-profile debate over how to save the region's iconic fish, the plant appears along more than one-third of the state's Pacific coastlines and along 43 percent of Puget Sound's 2,469-mile shore. Depending on how clear the water is, eelgrass can grow in depths of a few feet to a hundred feet.

When pasted against a forehead of beach at low tide, the slimy emerald-and-brown eelgrass leaves are underwhelming and are often mistaken for seaweed. But underwater, the plant acquires new grace. The plant's strap-shaped leaves (zoster is Greek for "belt") reach upward, toward the sun. The name, researchers suspect, derives from the plant's slinky waving motion when submerged. Divers who have drifted through eelgrass prairies liken the experience to wading through a green Iowa wheatfield stroked gently by a breeze.

Despite its appearance, eelgrass isn't actually a seaweed—seaweeds are algae, with no roots or flowers—but one of just 50 or so flowering plants that crept back to salt water when Tyrannosaurus rex still reigned on land. Life underwater poses new challenges for a plant. Consider sex: When it forsook the land, eelgrass waved goodbye to the wind, birds, and bees that deliver pollen. Today eelgrass spreads when the current carries the pollen to a flower. The resulting seed is borne away on a tiny air bubble, to colonize new ground. A perennial flowering plant—eelgrass can also "clone"itself by growing from its own rootstock—some eelgrass communities have been found to be a thousand years old. "Biologically, they're an evolutionary marvel," says Wyllie-Echeverria.

The mature eelgrass plant is also a veritable underwater ark. A forest of single-cell diatoms, algae, and bacteria live on the leaves, forming a distinctive brown felt that's rich in nutrients. In Northwest waters, some 18 additional organisms can pig-pile on top, joining an eat-and-be-eaten drama worthy of Wild Kingdom. Flagellates gorge on algae; crustaceanlike harpacticoid copepods feast on the flagellates. Puget Sound's juvenile chum salmon find the harpacticoid copepods as irresistible as beer nuts, says Simenstad. Though saddled at times with twice their mass in hangers-on, the eelgrass leaves keep reaching toward the light. The key to eelgrass keeping upright in the water column is the plant's built-in air channels and the bubbles of oxygen it produces during photosynthesis.

Pipefish, the pencil-like cousins of the seahorse, nose around eelgrass meadows, sucking up food through their soda-straw mouths. In spring vulnerable young Dungeness crabs enter the meadows to molt. Below the water, a mat of rhizomes from the plants hold in place a sandy, nutrient-rich soil that's home for all sorts of clams—from bent-nosed to soft-shells.

Two years ago, one 3,500-acre swath of Puget Sound was designated an Important Bird Area (IBA) by Audubon Washington, largely because of the vital role the rich eelgrass ecosystem plays for dozens of wintering birds, including the western grebe and the federally threatened marbled murrelet. The birds rely on the Pacific herring (and their eggs) as a major food source; the fish, in turn, rely on eelgrass for spawning habitat.

Few creatures actually eat the cellulose-heavy eelgrass, but each year the plant does fuel one amazing bird migration: After spending the summer breeding in the Arctic, nearly the entire Pacific Flyway population of brant geese—mostly Pacific brant but also a few western high Arctic brant—settles in Alaska's Izembek Lagoon and devours an estimated 2,000 tons, or about 2 percent, of the Pacific Coast's largest eelgrass stand. Fortified, the geese then fly more than 3,000 miles nonstop to Mexico.

Ecologists say that when eelgrass dies and decays, it becomes a lifesaver for other living things. As its leaves rot and fall away, various organisms munch the eelgrass into pieces. What the animals don't actually eat is coated by microbes, which extract nutrition from the ever-shrinking pieces. The process is repeated, and the dinner plate passes on to the next customer along the food chain. In this way eelgrass detritus supports a staggering amount of life. Ron Thom, a scientist at the Pacific Northwest National Laboratory and an expert in eelgrass restoration, does a back-of-the-envelope estimate: If the plant sheds and replaces its leaves seven times a year, Puget Sound's 27,200 acres of eelgrass may produce 3 billion pounds of detritus annually. That's a lot of dinner plates. "They're a major part the base of the food web," he says. Nobody can say for sure where all this detritus goes, but eelgrass has been found in the belly of an abyssal rattail fish 30,000 feet deep and well off the Oregon coast, leading scientists to wonder how far from shore this unassuming plant's influence extends.

No one knows how much seagrass may have vanished after Europeans arrived in the United States, though early dredging and pollution surely reduced or erased it in several places, including along Seattle's waterfront, says Tom Mumford, a marine biologist with Washington's Department of Natural Resources.

Time hasn't ended the insults: Logging and home development pour sediments into the shallow bays, estuaries, and tidelands eelgrass prefers. Tens of thousands of docks and boat slips block out the sunlight the plant needs to grow. One-third of Puget Sound's shorelines now have modifications such as bulkheads, many of which erode the seafloor of the sandy soils the plant requires.

Later in the day, in the tide shallows off another Hood Canal beach, Simenstad vacuums a final pan full of pinpoint-size bugs. Young sifts and pours them into a specimen bottle, to count later under a microscope. Juvenile chum salmon will travel up to 10 miles a day in spring as they graze the fringes of eelgrass beds for these harpacticoid copepods, which account for 80 percent of their diet. As we walk to shore, the bottom is blank, almost barren, and we startle a school of juvenile chum salmon. They rocket away briefly and then pause, seeming nervous and lost without a good patch of green.

"If we shift this corridor from a continuous buffet for the fish to fragmented habitat," says Simenstad, "then the question is, does that inhibit the fish’s fitness or ability to migrate?"

In the early 1990s, recognizing the importance of eelgrass, Washington State established a "no net loss" policy. As a result, projects that can affect eelgrass, such as a recent expansion of ferry terminals, must now be redesigned or else replace the eelgrass that's lost. But scientists haven't had much success re-creating large eelgrass meadows on the West Coast, says Thom of the Pacific Northwest National Laboratory.

"There was a time when we thought we could solve this problem relatively easily," says the University of Washington's Wyllie-Echeverria. "That time may be over. We're realizing that to save eelgrass will require an interdisciplinary effort of natural scientists, social scientists, legal experts, and ethicists. In a way, we're going to have to translate Aldo Leopold's land ethic to the ocean."

Christopher Solomon writes from Seattle for The New York Times, Outside, and Skiing. This is his first story for Audubon.