Aggregation, in oceanography, is a process that significantly alters the sizes, characteristics and abundances of suspended particles in the ocean. There are two major mechanisms for aggregation:

• biologically mediated aggregation, which occurs when small particles are aggregated into fecal pellets through the feeding activities of animals; and,

• aggregation via the largely physical processes of collision and sticking, i.e. coagulation.

The impacts of aggregation on marine ecosystems include:

• much of the particulate matter reaching the ocean interior and sea floor sinks as large, rapidly settling aggregates of detritus, mucous, algae and microorganisms in the visible size range, i.e. marine snow, so the export of carbon and nutrients from the surface ocean is directly linked to the mechanisms responsible for combining small particles into larger units capable of rapid settlement, i.e. aggregation;

• aggregation of small organisms and other organic particles affects the abilities of grazers to isolate their food from the aquatic environment and makes more food available to large–particle feeders;

• aggregation produces particles large enough to maintain unique internal chemical environments that can support unusual, microbial communities and potentially provide island–like refuges for protozoa and micorozooplankton; and

• aggregation affects the optical properties of seawater by altering the size distribution and abundance of particles available to absorb and scatter sunlight.

Further Reading

• Peter Saundry. 2011. Seas of the world. Topic ed. C.Michael Hogan. Ed.-in-chief Cutler J.Cleveland. Encyclopedia of Earth

• A. L. Alldredge and G. A. Jackson. Aggregation in marine systems: preface. DSR II, 42:1–7, 1995.