Mud sucks—literally. On land, it squishes underfoot and slimes your shoes. In seaside shallows, it clutches your feet and tugs with the ferocity of an angry alligator.
I know. Wading back to shore after fieldwork with Bodega Marine Lab scientists in Tomales Bay, I lost my balance and plunged into what felt like slow-hardening concrete. Every time I tried to pry my foot loose, I lurched back into the sludge. A graduate student reached out to help—only to skid into the ooze next to me.
“Get on all fours!” she commanded. “When you’re stuck this deep in mud, crawling is your only option.” And so we started creeping like derelict dogs toward shore.
“Wow!” she suddenly exclaimed. “Check out the infauna!”
My baptism by mud introduced me to the scientific term for animals that live in the soft silt of bays and estuaries. Lacking the majesty of cliffs or the allure of beaches, mudflats — the ugly stepsisters of shore habitats — shelter a rich array of unseen, under-appreciated marine creatures.
The ebb and flow of the tides and the mix of fresh and salt water create a Goldilocks environment—not too salty, not too fresh. Here, tiny residents—mostly invertebrates less than two inches long—tunnel through the muck, filtering food and oxygen while recycling nutrients. Without them, the entire oceanic food web, from mollusks to fish to birds, would collapse.
Mud is worm territory. Most common on the Northern California coast are segmented polychaetes (Greek for “many bristles”), relatives of earthworms named for the spikes that help them crawl, dig or swim. Some of these architects and engineers build tubes of sand or mucus that stabilize sediment. Others ventilate the mud as they burrow and feed. Lugworms, another polychaete, suck in sand and mud, extract organic nutrients and deposit slender coils of “castings” (a scientific term for poop) outside the burrow entrances.
A hidden workforce of burrowing bivalves, including native littleneck clams, pock the surface with holes and dimples. Buried several inches deep, they extend siphons upward to draw seawater across their gills and filter plankton and other morsels. By clarifying water and recycling nutrients, these quiet custodians keep the ecosystem humming—and feed hungry predators that range from shorebirds to Dungeness crabs to humans.
Ghost shrimp — pale, almost transparent crustaceans — are the phantoms of this underworld. Despite their seeming fragility, they wield an oversized claw (sometimes a quarter of their weight) to push mud and sand to the surface, creating miniature volcano-like mounds. Inside, a branching burrow shelters their otherwise defenseless bodies.
Oyster drills, small snails with elegant whorled shells, don’t look deadly—but they are. Unleashing their sandpaper-like tongues, they bore through the shells of oysters, mussels and barnacles, then suck out the juicy contents. When the snails die, hermit crabs scurry to claim their abandoned shells as temporary housing.
Platoons of miniature ninjas serve as clean-up crew. Shrimp-like amphipods shred detritus in Y-shaped burrows. Armored isopods—the “pill bugs of the sea”—munch decaying plants. Nematodes (better known as roundworms) gobble bacteria. Together, they break down organic matter, turning waste into worm food.
My unanticipated adventure in mud-raking left me with salt-laced hair, crusted waders and a renewed sense of wonder. Never again will I dismiss a mudscape as a drab dead zone between land and sea. Mud lives—and its creeping, crawling, scouring, scooting, hunting, harvesting minions help keep our oceans alive and healthy.
Photo credits: UCDavis Coastal and Marine Sciences Institute, Wikipedia Commons
