Each of the bright red cells in this image is part of a colony of Pseudendoclonium submarinum. The cells (about 3-5 µm across) appear red here, because this image was captured at an epifluorescence microscope, and the cells were being excited with blue light. The result of the blue-light excitement in algae is the return of bright-red fluorescence of chlorophyll. The algal cells are shown here growing on a naturally-decaying blade of smooth cordgrass (Spartina alterniflora), visible as faintly green fluorescence beneath the algal cells. This microalga is virtually always present as a thin veneer on decaying cordgrass blades, and is very likely to interact with ascomycetous decomposers such as Phaeosphaeria spartinicola. The alga may provide oxygen and organic photosynthate to the fungus; the fungus may provide carbon-dioxide (and other molecules?) to the alga. When alga and ascomycete are paired in culture, they readily intermingle, and each appears to promote growth of the other. See Newell, 1993, Adv Microb Ecol 13:301-326; Newell & Porter, 2000, pp. 159-185, in Weinstein & Kreeger, Concepts and Controversies in Tidal Marsh Ecology, Kluwer.