Most photosynthesis occurs in a biofilm of diatoms, cyanobacteria, and flagellates (e.g., euglena) that is visible at low tide. Coloring the tidal flats green or brown, these microorganisms migrate 1 or 2 millimeters down into the mud just before the tide returns. Green filamentous algae (Enteromorpha spp.) will grow if attachment sites are available.
Crabs and snails are common members of the epifauna, permanent residents of the surface. Fiddler crabs are active at low tide; Europe’s shore crabs are active when the mudflat is under water. These animals consume detritus and scavenge beached carcasses.
An infauna of copepods, nematodes, and flatworms (turbellarians) is abundant and lives with a macrofauna of bivalves, crustaceans, various types of worm, anemones, and brittlestars—the last two burrowing into the mud. In order to survive low oxygen levels, many have evolved ways to draw oxygenated water into their burrows during high water and store it for use during low water.
Shorebirds such as herons and egrets are common predators at low tide; fish such as flounders hunt when the flats are inundated.