In biology, detritus is dead particulate organic material,
as distinguished from dissolved organic material.
Detritus typically includes the bodies or fragments
of bodies of dead organisms, and fecal material.
Detritus typically hosts communities of microorganisms
that colonize and decompose it.

Marine snow is a shower of organic material falling from
upper waters to the deep ocean. ... Some flakes fall for
weeks before finally reaching the ocean floor. As plants
and animals near the surface of the ocean die and decay,
they fall toward the seafloor, just like leaves and decaying
material fall onto a forest floor.