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Microbial Foam (Biotic Subclass)

Component: Biotic

Unique Identifier: 418

Biotic Setting Planktonic Biota
Biotic Class Floating/Suspended Microbes
Biotic Subclass Microbial Foam

Definition Aggregations of microbes within the foam matrix that forms on the water's surface. Sea foam is the foam the lies on the sea surface, in the surf zone and at times on intertidal areas, created from dissolved organic compounds when air is forcefully injected into the water column (Harden and Williams 1989). Foam formation is aided by properties of lignans, proteins and carbohydrates that act as surfactants or foaming agents. The large area presented by the micro-bubbles composing seafoam is an ideal surface for concentration and adherence of microbial communities including bacteria, viruses and microscopic plankton. The characteristics of the air-water interface, and particularly of sea foam are unique compared to the bulk water column (Lion and Leckie 1981) and possess unique physical and chemical properties. The foams are well-oxygenated, sites of photolytic processes and tend to support high levels of aerobic metabolism with high organic processing rates. Surface foam is the site of intense trophic activity at the microbial level because of the concentration of microbial biomass, sugars, lipids and other growth compounds and thus represents an important part of the marine microbial food web. Concentration and transformation of trace metals, nutrient compounds, contaminants and pollutants also occurs in sea foam and can enter the food web via microbial pathways. The properties of the foam have also been identified as delivering growth-promoting nutrients and organic material to seagrass and kelp communities.