The many creatures that dig into the sediments at the bottom of the ocean are ecosystem engineers. Their burrowing, foraging, and even pooping change the ocean landscape—not just close by, but miles away.

Sediments have been described as the oceans’ compost heaps. They contain bits of rock and dirt washed out to sea by rivers. They also contain bits of organic material—everything from dead skin cells to the wastes of all the fish and other animals in the water above. And they’re loaded with bacteria and algae.

Many organisms spend much or all of their lives near the bottom—from shallow coastal waters to the deepest ocean trenches. That includes worms, fish, crustaceans, and others.

These critters dig burrows to protect them from predators or provide a safe haven for mating. They sculpt patterns in the soft sand or mud to attract mates. They poke through the sediments to scare up food. Some even scoop up the sediments, filter out tasty morsels, then poop out everything that’s not edible.

All of that activity changes things. It moves sediments from one spot to another. It scatters bacteria. It lifts eggs into the water. It brings nutrients to microscopic organisms.

The immediate effects are on a small scale—over a few inches or feet. But they add up. Most of the sea floor is covered with sediments, and as long as there is oxygen, there are animals burrowing and moving the sediments around. So the effects of all these ecosystem engineers add up.