ORGANIC AGGREGATES IN SEAWATER AND THE DYNAMICS OF THEIR FORMATION AND UTILIZATION

Abstract

Much of the nonliving particulate organic matter in seawater consists of delicate, plate‐like aggregates ranging in size from about 5 µ to several mm in diameter. The aggregates are amorphous matrices containing both organic and inorganic materials, with inclusions of bacteria and phytoplankton. Descriptive information herein deals primarily with a two‐year series of observations in Long Island Sound. A consistent bimodal seasonal cycle has been found, with peaks in winter and early summer. These aggregates appear to be formed mainly by adsorption of dissolved organic matter on bubbles and other naturally occurring surfaces in the sea, a process readily duplicated under experimental conditions. Naturally occurring aggregates provide a substrate for bacterial growth and probably food for animals. They are present during certain seasons when phytoplankton is scarce and probably serve an important function as supplementary food for zooplankton under such circumstances. The presence of aggregates is an oceanic as well as a coastal phenomenon and is believed to have general ecological significance. A concept is developed that the reversible reaction between dissolved and particulate matter tends to stabilize the marine association, and there are suggestions of community adaptation in the development of this system.