There's Life in the Mud

June-July 2005

This is an article from WaveLength Magazine, available in print in North America and globally on the web.
To download a pdf copy of the magazine click here: > DOWNLOAD

by Neil Schulman

Willapa Bay oysters.

"There’s not enough water to paddle,” says Tina. “So I guess we should just walk out there and see what’s for dinner.”

We put on our big rubber boots and walk out onto the mudflats of Willapa Bay. The mud sucks at our boots with strange slurping sounds and we move quickly to avoid sinking in. Half an hour later, we’re walking back with heavy bags of oysters and clams.

Stuffing yourself with shellfish is just one reminder that estuaries are one of the richest ecosystems on earth. But how many of us know what really happens down there in the mud?

WHAT IS AN ESTUARY ANYWAY?

Estuaries are where freshwater rivers meet the sea. When two ecosystems meet, high biological diversity is usually the result, and estuaries are no exception. On the west coast of North America, most estuaries are shallow bays with slow-moving rivers winding their way into the sea behind the shelter of a protective sandbar—the legacy of rising sea levels flooding the land at the end of the last ice age. Add protection from the surf, mixing of saltwater and fresh, and the slowed movement of the river. Now put it along the Pacific Flyway, and you’ve got the recipe for a rich ecological stew.

GET DOWN WITH DETRITUS

If you’re not a naturalist, estuaries at low tide can look pretty barren: sand, mud, brackish water and some tree trunks. But you’ll see shorebirds probing in the soft mud at the very edge of the tide. Take a clue from these birds—they’re crashing one of the biggest ecological parties on the earth: a food chain based on detritus.

When rivers flow into estuaries, they slow down because of the flat coastal landscape and the wedge of saltwater pushing in from the ocean at every rising tide. As the rivers slow, they drop whatever they’re carrying— sediment and bits of decaying wood, leaves and other organic matter. Such detritus drives almost the whole estuarine food chain. In fact, estuarine productivity can be estimated quickly by the speed of the river entering the sea—the slower the better, because more debris is dropped out of the water column to fertilize the estuary. Estuaries with slow-moving rivers like Willapa Bay are far more productive than some of those which have a much higher flow.

LIFE ON THE MUDFLATS

The master chef of the mudflat detrital salad bar is an unassuming critter most humans call ‘bait’: ghost shrimp. Walk across a mudflat, and you’ll see small volcano-like holes in the mud. These are the ends of the shrimp’s U-shaped tunnels. Water flows into the tunnels and out the other end at high tide, which brings roomservice nutrients to the shrimp, who never have to venture into the dangerous world above. A host of critters take advantage of this conveyer belt of food, like the cryptomaya clam, pea crab, and a fish called goby. The shrimp keep water, oxygen and nutrients circulating through this giant, muddy world. Mudflats may not be sexy, but if you want biomass, they’re the place to be.

THE EELGRASS ZONE—A QUIET PLACE TO RAISE LARVAE

In the 10,000 years since the ice age, spits have built up on the outside of most West Coast estuaries, providing shelter from the pounding surf. Behind this protective spit, out past the mudflats, you’ll find the eelgrass beds: an estuarine city below the low-tide line.

Like whales, eelgrass is a former land dweller that returned to the sea. Eelgrass beds host more species-diversity per square foot than anywhere other than a coral reef, with their own networks of producers, predators, and decomposers. The eelgrass roots—their legacy from living on land— allow them to take advantage of the rich underwater soils like no aquatic plant can. Eelgrass forms underwater forests like kelp beds at sea. To sea life, eelgrass is like the suburbs are for humans—a protected environment and a good place to raise young, outside the hustle and bustle of the open sea or the rushing river. And the eelgrass even has lots of good ‘schools’— salmon, flounder, sole, crab larvae, herring, and other keystone species of the river and sea grow up in the protection of the eelgrass beds. Nine of every ten species of fish caught commercially spend part of their lives in an estuary. Migrating loons, ducks and geese, especially brant and diving ducks like scaup and redhead, hop from eelgrass bed to eelgrass bed on their way up and down the Pacific Coast.

One of the strangest-looking eelgrass residents is the bay pipefish, which sports some of the best camouflage around. The sight of a bay pipefish is well worth the price of a mask and snorkel (or aquarium admission) alone. It looks just like a piece of eelgrass, but if you watch for long enough, you’ll spot the eyes.

GROWING HUMAN IMPACT

From San Francisco to Anchorage, most coastal cities and towns are on estuaries. Like ghost shrimp, humans were attracted to the natural richness, flat land, and access to both rivers and sea. Our cities are growing, and also growing is the amount of pavement, water pollution, sediment runoff, sewage, dredging of eelgrass beds and habitat loss. The Pew Charitable Trust’s Report on Coastal Sprawl found that estuaries become biologically degraded when just 10% of the entire watershed is paved.

Invasive Spartina at Willapa Bay.

GRASS GONE BAD

Another threat to estuaries is more sneaky—an invasive grass known as Spartina, which is invading bays from California to BC. Also known as cordgrass, three species of Spartina hail from North America’s East Coast and from Britain. Their nasty habit is colonizing the open mudflats and turning the giant detrital salad bar into a far less productive monoculture meadow. Spartina is also threatening to take human enterprise—like the oyster industry in Willapa Bay—down the ecological tubes with it.

STAND UP FOR YOUR FAVORITE MUDFLAT

Paddlers, along with commercial and recreational fishermen, are one of only a few natural constituencies for estuaries. Mudflats and eelgrass beds don’t have the charismatic appeal of high mountains, coral reefs, or rain forests. Find a way to put your paddle down for a few days and do what you can to protect estuaries. One example is the WAKE club in Bellingham, Washington (Whatcom Association of Kayak Enthusiasts) that has helped in mapping Spartina’s spread in Puget Sound. It’s critical to become active out of your boat—to advocate for protecting estuaries, better treatment of wastewater and runoff and better land use by us pesky humans. It’s the right thing to do. And somewhere, silently, a lowly ghost shrimp will thank you.

© Text and photos by Neil Schulman, a paddler, writer and photographer in Portland, Oregon. A former coastal ecology instructor, he keeps a pair of rubber boots in his car at all times.