Development of a freshwater periphyton community as influenced by diatom mucilages

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Abstract
The function of diatom mucilage in the formation of spatially complex periphyton communities was investigated in McConaughy reservoir (Nebraska, U.S.A.). Seasonal biofilms on natural and artificial substrates revealed high densities of periphytic diatoms (up to 3.5 × 104 cells mm-2). Growth habits of the dominant taxa (short stalk, Achnanthes minutissima; long stalk, Cymbella affinis and Gomphonema olivaceum; rosette, Fragilaria vaucheriae and Synedra radians) depend on the mucilage morphology. The volume of stalk mucilage in late stages of community development was estimated to be more than two times the volume of the cells producing it. When the periphytic biomass exceeded the carrying capacity of its substrate, portions of the community were sloughed, resulting in the loss of the upper story of cells and mucilage. Diatom mucilage affects community structure as follows: (i) it allows cell–surface adhesion; (ii) stalks of Cym. affinis provide increased surface area for attachment by Ach. minutissima; (iii) dense canopies of long-stalked Cym. affinis and Gomphonema olivaceum trap euplanktonic algae which have settled into the periphyton; (iv) mucilage binds detrital particulates; (v) stalked diatoms enable vertical stratification in the community, as spring collections revealed the development of an upper tier composed of Gomphonema olivaceum and Cym. affinis covering a lower tier dominated by F. vaucheriae and Stephanodiscus minutula.