In the undersea world, coral reefs and tidepools get all the press. The intertidal zone is like Manhattan—crowded, stressful, loud. Coral reefs are like Paris—famous, cultured, and showy. Bays are more like the suburbs.
But the sheltered parts of the coast are lively in their own right, and filled with some funky and unique creatures. Like the suburbs, there’s a lot going on beneath the placid exterior.
The Ocean’s Suburbs
Bays and Estuaries form calm bays, sheltered from the worst of ocean waves, and where infusions of freshwater meet the sea. Like northern New Jersey or San Francisco’s East Bay, it’s a refuge for creatures that want to be able to access the salty part of the sea, but can’t afford the competition for expense real estate of the tidepool or reef. Or maybe they want a quieter lifestyle and room to spread out, the aquatic equivalent of a backyard and garage. Chesapeake Bay, San Francisco Bay and similar bays around the globe are protected from big ocean swell, and offer a vast soft sandy bottom for aspiring suburbanites to burrow in.
A Social Mixer
Bays offer more than just protection from the pounding surf. Most (but not all) bays contain river mouths. They combine the protection from the sea with the mixing of fresh and salt water. For example San Francisco collects most of the fresh water from the Sierra Nevada and the Central Valley. The water composition of bays is constantly in flux, changing with the amount of river flow, rain, and snowmelt, and the height of the tide.
A Good Place to Raise the Larvae
In this mixing zone, food is plentiful. Ocean tides wash nutrients into the still water of the bay, where they’re easy pickings. Rivers carry food-rich sediment, logs and branches, leaf material, and other sources of food into the bay, where they hit still water and settle out. This makes the Bay a great place to feed kids, whatever the species. Kids eat a lot, and in the Bay there’s plenty of food.
And in addition to the pounding, many predators don’t make the journey from the sea. Bays are mostly free of the big bad boys of the ocean—large sharks, killer whales, and such. (Australia’s Estuarine Crocodiles are the notable exception.) There certainly are plenty of predators, like Great Blue Herons that line the banks of bays looking for unsuspecting fish on the edges—but it’s easier living than the mean streets of the reef.
The Nice Green Eelgrass Lawns
The main element of bays around the world is a plant called Eelgrass. Eelgrass, is a land plant that, like whales, returned to the sea. In the mild environment of the bay, it set its roots in sandy and muddy bottoms, and eelgrass beds provide a source of food and a hiding place for a variety of creatures, as well as a handy substrate for attaching eggs to.
The Suburbs Have Good “Schools”
Given this sheltered environment, it’s not surprising that many fish love estuaries. In fact, they’re essential to the life cycles of most commercially caught species of fish and clams around the world. Salmon, crabs, flounder, and a variety of other commercial species—totaling 70% of the US’s commercial fishery in terms of commercial value.
Like any desirable suburb, bays provide easy access to where you can make a living: in this case, easy access to the reefs and the continental shelf. A lot species make the commute, breeding in estuaries before heading into the wider world to make a living. Then, when it comes time to raise kids of their own, it’s back to the suburbs to raise a family.
What Hides Beneath
But that doesn’t mean life in the ocean’s suburbs is obvious. Just like idyllic suburbs can conceal all kinds of wackiness, from nasty school board politics to the occasional Russian spy, a lot goes on in bays that we don’t see. In bays, a lot of it’s in the mud. Wait for the tide to go out, and you’ll usually see a repeating pattern of holes as identical as the tract houses in a new subdivision. These are made by creatures like Ghost Shrimp and blue mud shrimp, which dig a series of burrows that house other creatures that take advantage of the free housing—no HOA rules here. Clams burrow into the mud, crabs run around cleaning up any detritus, and the Bay Pipefish blends in with the eelgrass so closely they’re hard to see, even in an aquarium tank. It’s not like you can’t find a party in the suburbs. You just need to look a little harder.