Marine Snow Definition

Marine snow refers to organic particulate matter that constantly falls from the upper waters into the deeper waters of the ocean. Marine snow serves to provide food and energy from the productive upper waters exposed to sunlight to the marine organisms that reside in the deeper regions of the water column. The content and abundance of marine snow varies seasonally and with variations in ocean currents. This is largely due to the seasonal changes in light and resources available to the organisms in the upper water column.

Marine Snow Characteristics

Marine snow is comprised of primarily organic particulate matter derived from the bodies of phytoplankton, feces, and decaying plant materials. These particulates typically join to form larger aggregates that are coated in mucus created by bacterial, zooplankton, and phytoplankton species. As these aggregates sink toward the ocean floor, they often accumulate additional particles, and can grow up to several centimeters in size. Since the abundance of marine snow changes with the seasons and nutrient abundance in the upper waters, the abundance of marine snow often increases during algae blooms (pictured below) as a result of increased phytoplankton growth. It is also hypothesized that marine snow is involved in nutrient recycling within marine environments. In this way, the particulates both provide food for the organisms that reside in the deep waters, but also help to decompose the organic matter residing at the ocean floor (e.g., fecal matter) via the bacterial species that comprise the particulates of marine snow.

Algae bloom


1. Which of the following is NOT a feature of marine snow?
A. Marine snow is comprised primarily of inorganic matter.
B. Marine snow is more abundant during the winter months.
C. Marine snow is toxic to organisms that reside in the deeper waters of the ocean.
D. None of the above are features of marine snow.

Answer to Question #1
D is correct. None of these responses are features of marine snow. Marine snow is comprised primarily of organic matter derived from organisms that reside at the surface waters, such as phytoplankton. Since these organisms depend on sunlight and nutrient availability, there is typically a greater abundance of marine snow during the summer months. Marine snow is a food source to many organisms that reside within the deeper waters, and thus is an effective means of moving energy through the water column. Thus, marine snow is not toxic to the animals inhabiting the deeper regions of the ocean.


  • “Marine snow falls heaviest at the Equator.” (2017). Nature. Oct 1e1;550(7675):158. doi: 10.1038/550158b.
  • Sun et al. (2017). Light-induced aggregation of microbial exopolymeric substances. Chemoshere. Aug;181:675-681.
  • Tansel, B. (2018). Morphology, composition and aggregation mechanisms of soft bioflocs in marine snow and activated sludge: A comparative review. J Environ Mange. 205:231-243.