A raft of sea otters floating together on their backs in calm shallow water, wrapped in kelp, with one in the foreground looking up

Coastal wetlands

Coastal wetlands are low-lying stretches of land saturated with water.

They can often be found inland from beaches and edged in muddy, soft ground. These shallow swamps, marshes and estuaries are home to an abundant mix of plants, fish and wildlife.

How species adapt

The water in coastal wetlands determines the kinds of plants and animals that live there. The water may be salty or fresh. Some wetlands are always wet, while others dry out for periods of time. Tides bring in seawater from the ocean, and with it, tiny particles of decaying plants and animals called detritus. Animals like fat innkeeper worms, bent-nose clams, and skeleton shrimp thrive on these nutrient-rich particles. In turn, these animals become food for thousands of different kinds of birds, fish, and wildlife.

Marine life in the mud

Receding tides expose rich, dark mud crowded with crabs, shrimps, worms, snails, clams, and other animals. The mud helps to hide these animals from birds and other hungry predators, and protects them from changes in air temperature and water conditions.

A wide-angle view of Elkhorn Slough under a clear blue sky, showing calm water, cracked mud flats, and wooded hills — The Elkhorn Slough National Estuarine Research Reserve

A row of six white terns perched on old wooden posts rising from blue water, with grassy wetlands and trees in the background — Terns in Elkhorn Slough

Salt-loving plants

Saltmarshes form when high tides flood the ground above the mud flats. Most plants would wither and die in these wet, salty conditions, but certain salt-tolerant plants thrive. Pickleweed concentrates salt in the tips of its stems and then drops its tips in the fall, discarding the salt. Salt grasses have special glands that secrete the salt absorbed from the water.

Underwater camouflage

Eelgrass is one of the few plants that grow under the water in coastal wetlands. Its matted roots trap sediments, helping to keep the mud in place. Pipefish and skeleton shrimp attach themselves to eelgrass blades to camouflage their long narrow bodies, swaying in the current along with the eelgrass.

Seasonal breeding grounds

Bat rays enter sloughs and bays in the summer to give birth to their young. They flap their wings to clear away mud and suck up their prey—clams, shrimp, worms and other invertebrates. Leopard sharks also enter coastal wetlands to give birth. Sea otters, too, raise their pups here and forage for food in the shallow wetland waters.

A refuge for endangered species

Nearly 75 percent of rare or endangered bird species rely on wetland habitats.

A bay pipefish swims among the eelgrass, blending in with its surroundings

A pair of sea otters interacting in the water at Elkhorn Slough, with a colony of brown pelicans gathered on the shore behind them

A skeleton shrimp sways its long, narrow body in the current while attached to seaweed.

A bay pipefish (Syngnathus leptorhynchus) swims among the eelgrass, blending in with its surroundings.

Bays and wetlands serve as important nursery and feeding grounds for bat rays (Myliobatis californica).

Southern sea otters (Enhydra lutris nereis) seek out coastal wetlands to shelter and raise their pups.

A skeleton shrimp (Caprella spp.) sways its long, narrow body in the current while attached to seaweed.

How this habitat changes

After winter rains, fresh water runs off the surrounding land and mixes with the wetland’s salty water, creating an ideal habitat for many juvenile species of fish. During storms, wetlands act as sponges, capturing and slowly releasing water that runs off from land. Wetlands also absorb wave surges and protect inland areas from flooding.

A rest stop for migrating birds

In spring and fall, thousands of migrating birds stop at coastal wetlands to rest, feed and breed. Curlews, godwits and willets probe the mud with their long bills, hunting for burrowing crabs, worms, and snails. Grebes and pelicans dive into adjacent waters to scoop up fish, while mallards and other ducks bob for algae.

A marbled godwit in the Sandy Shore gallery at Monterey Bay Aquarium.

An ecosystem powerhouse

Not only are coastal wetlands important habitat for a wide range of wildlife, they provide important benefits to people and the planet. Coastal wetlands improve water clarity by filtering polluted runoff and absorbing excess nutrients. And they support commercial fisheries that are vital to California’s coastal economy. Wetlands also sequester carbon in the underlying sediments; and protect our shoreline from erosion by absorbing wave energy and helping to mitigate sea level rise.

Several white great egrets spread their wings and step through shallow water while dark waterbirds swim in the foreground — Great egrets, a snowy egret, and other shorebirds spotted in Elkhorn Slough.

A disappearing resource

In the past, most people considered wetlands to be wastelands—places to be drained, plowed, filled, and developed. Since the 1850s, 90 percent of California’s coastal wetlands have been destroyed. Though this destruction has slowed, the country’s remaining wetlands are still threatened by a growing human population. The need for more homes and more food means continued pressure to drain and destroy this habitat.

Pesticides and pollution from urban runoff and invasive plant species also threaten this habitat.

Things to look for and notice

Great blue herons live year-round in coastal wetlands. Look for them standing still in shallow water, quietly waiting to snatch up small fish. In early spring, great blue herons build nests in the tops of nearby trees.

A great blue heron sitting on ice plant along the coast of Monterey Bay. — A great blue heron (*Ardea herodias*) seen off the coast of Monterey Bay.

How to enjoy and protect this habitat

Coastal wetlands are scenic, peaceful places to observe wildlife. Stay on designated trails when visiting, and be mindful of the animals and plants that depend on this fragile ecosystem.

What you can do

At home, you can help preserve this critical habitat by keeping sidewalks, lawns, and driveways clear of pet waste, trash, toxic chemicals, fertilizers and motor oil. All of these pollutants can wash into storm drains and end up in our wetlands. Use native species when planting trees, shrubs, and flowers to help preserve the ecological balance of local wetlands.