Some organisms arrive on the snow through their association with animal excrement. Microbes from the guts of marine animals are excreted in feces, becoming part of the snow community when the fecal matter sticks to growing snow particles. The communities of microorganisms change the chemistry of the snow from that of the surrounding water. Alldredge says the microhabitats on the particles can become anaerobic, meaning without oxygen. Species of bacteria that grow under those conditions find the snow suits them much better than the water.
Marine snow can also be a reservoir for other important elements, like nitrogen.
The particles are also concentrated sources of carbon, and play an important role in carbon cycling, says Alldredge. Microorganisms aren't alone on the snow. The larval worms and crabs survive by eating the organisms on the particle as the snow falls to the seafloor. The phytoplankton that capture the sun's energy by photosynthesis can only do so where the sun can penetrate the ocean depth. In the clearest of waters, that is only a couple hundred meters down.