Eelgrass

ARTICLE Intro Eelgrass 512x219

I believe a leaf of grass is no less than the journey work of the stars,
And the pismire is equally perfect, and a grain of sand, and the egg
of the wren,
And the tree-toad is a chef-d’oeuvre for the highest,
And the running blackberry would adorn the parlors of heaven,
And the narrowest hinge in my hand puts to scorn all machinery,
And the cow crunching with depress’d head surpasses any statue,
And a mouse is miracle enough to stagger sextillions of infidels.

-Walt Whitman, Leaves of Grass


As storms cross the Coast Range of western Oregon—ferried along by its not-so-pacific ocean—their clouds cool and condense with altitude, dumping ample precipitation as they’re pushed inland. Dozens of rivers carry this runoff (including snowmelt) down and seaward, flowing from mountain to delta eventually into the Pacific, whence the waters came. Wherever this abundant freshwater admixes with the salt of the sea, an estuary is formed—the confluence of two distinct milieux, an ecological mash-up of species and habitats literally teeming with life.

Brackish and intertidal, estuaries act as a sort of staging ground for many marine species, and Siletz Bay is a prime example. The Siletz River empties out here, and the resulting delta is a miles-wide expanse of mudflats and salt marsh riven with snaking tidal channels. What makes Siletz Bay special is not merely mud, though, but what lives in the mud: eelgrass, specifically native Zostera marina, or common eelgrass, and the exotic Zostera japonica, accidently introduced on the shells of non-native oysters. A combination of nutrient-rich substrate, pancake-flat shoreline, and mild winter weather allow the eelgrasses to flourish in the bay. 

The plants produce both sexually—with flowers and seeds—and by cloning, sprouting repeatedly from their root-like rhizomes to form dense colonies called genets. Because the two species have differing preferences for sunlight, temperature, and water turbidity, they seem to naturally divvy up the shoreline, occupying their respective niches with little overlap. Z. japonica, the invader, occurs close to shore in often sediment-clouded water, tolerant of long intertidal exposures.  Z. marina prefers slightly deeper, cooler, clearer water.

It is difficult to overestimate the importance of Z. marina, the common eelgrass. Fast-growing and adaptive, it is the most widespread flowering marine plant in the Northern Hemisphere. A single acre of eelgrass produces almost ten tons of leaves annually—a rate of productivity rivaling that of tropical rainforests—and every aspect of the plant’s lifecycle benefits the estuary.

Eelgrass and other similarly-adapted marsh plants capture as much as three times the solar energy of most agricultural crops. Ribbon-like leaves flutter freely in the surf, casting little shade on neighbors while exposing as much surface area as possible to sunlight. Like acres-wide swaths of solar panels, genets of eelgrass carpet sun-splashed mudflats and turn light into sugar into leaves into life.

As the grass grows, carbon dioxide is sequestered in the leaves and oxygen released, aerating the turbid shallows. Healthy beds of grass act dually as wavebreak and smokescreen, sheltering larvae of myriad species from surf and predation: Organisms as diverse as crabs and clams to nudibranchs and snails to stickleback and salmon find refuge in the tangle. The leaves themselves become habitat to epiphytes like sponges and bryozoans, and the rhizomes—the stems of the plant buried in mud—form a rootwork that is a haven for worms and other benthic invertebrates. When the leaves die off in winter, a whole suite of detritivores arise to capitalize on the windfall, recycling the nutrients back into the substrate with their waste.

Of course, all this fecundity in the eelgrass doesn’t escape the notice of other creatures, particularly those with a bird’s-eye view of the land. Ducks, gulls, herons, terns, osprey, eagles, and kingfishers flock to the flats at low tide to feast on the seafood buffet, while Brant geese—who migrate more than 3,000 miles in the fall from their northern nesting grounds—come solely for the grass, which they eat almost exclusively. Larger animals such as Mink and River Otters will sometimes forage in the mud, and Harbor Seals commonly haul out on the flats to sunbathe. This is a locus for trophic activity, a delicate food-web stretched out for miles. The mudflats and its denizens nourish life from the grassroots on up.