Marine snow & microbial exopolymers

Marine Snow – a constant shower of living and dead material that fall from the upper regions of the ocean, or the light-rich photic zone, to the aphotic (light-depleted) zone of the deep ocean.

Marine snow is made up mostly of organic matter, such as living and dead plankton, algae, and protists, as well as inorganic matter, such as sand, dust, microplastics, and even oil droplets. These particulates are all held together and aggregated by mucous (affectionately called exopolymeric substances by scientists) that is secreted by marine microbes like phytoplankton and bacteria.

As marine snow aggregates sink through the water column, they grow larger and accumulate other aggregates. They are also an important food source for filter-feeding creatures that exist in the water column. Those aggregates that are large enough to sink all the way to the ocean floor provide an important source of nutrients to an otherwise nutrient depleted environment.

The source and fate of marine snow in the oceans (source:

The source and fate of marine snow in the oceans (source:

In the diagram to the right you can see some of the ways that marine snow is important for marine food webs and nutrient cycling.

Notice that a majority of activity takes place within the upper 1,000 meters of the water column. The photic zone (also known as the epipelagic zone) is near the surface of the sea where there is enough light for photosynthesis to take place. This zone usually extends down to 200 meters.

From 200 to 1,000 meters is the mesopelagic (or twilight) zone. Many creatures, including swordfish, squid, wolf eels, and cuttlefish live in this zone. Since it is too dark for photosynthesis to take place in this zone, creatures who live here tend to be herbivores, carnivores, and detritivores (animals that feed on dead organisms or fecal pellets).


During the Deepwater Horizon oil spill, researchers noticed an explosion of large aggregates of marine snow near the surface of the water and in the water column. This indicated that perhaps the phytoplankton and bacteria in the water were secreting larger amounts of exopolymeric substances that normal.

This lead ADDOMEx researchers to begin investigating how the introduction oil and Corexit into the Gulf’s ecosystem caused a change in the natural marine snow formation processes of phytoplankton and bacteria. This  new marine snow was observed to collect a large amount of tiny oil droplets, hence it was termed “marine oil snow” or MOS. Researchers found that the MOS sank through the water column much faster, transporting large quantities of oil from the surface and sub-surface of the ocean to the seafloor.


October 2017
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Funded by: GoMRI