Mud Flats
The expansive mud flats that are uncovered as the tide recedes are home to a variety of organisms. Tiny one-celled algae (photosynthetic protists) called diatoms live on the surface of the mud at low tide. On a sunny day they can be seen as a greenish, orange slick on the mud surface. The diatoms migrate up and down in the mud (1-2 mm) with the tides, below the surface at high tide and to the surface at low tide. Their vertical migration helps them avoid invertebrates that comb the surface of the mud for food (eg., snails) and also helps them avoid being swept away with the tide.
The mud also provides a habitat for a number of tube dwelling animals. One of the most numerous inhabitants of the mud are amphipods called Corophium. With as many as 50,000 per square metre, they are one of the primary food sources for shore birds. Corophium feed by beating their legs to draw current through their U-shaped tube and filter out small particles of food. If you listen carefully, you may be able to hear the “snap, crackle, pop” of the Corophium opening and closing their tubes.
There are other tube dwelling animals in the mud:
annelid worms that live in tubes emerge to catch prey as they pass by or leave their tubes at night to forage for food
and
little Macoma clams that create a star pattern around their burrows when they reach out .
Why are tube dwelling animals so common on mud flats?
One possible reason is to avoid being swept away with the tides.
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