River Epilithon: Toward a Structural-Functional Model

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Abstract
Data are presented to show that a vigorous epilithon develops both on the upper and lower surfaces of rock and plastic substrates anchored in boreal rivers. This epilithic community is usually much more extensive on the upper surface, but the epilithon on the lower surface is sometimes equally well developed and often contains large numbers of chlorophyll-containing microorganisms. Morphological evidence suggests grazing of the epilithon by invertebrates, and clearly shows that the cellular components of this sessile community grow in distinct microclonies within a continuous fibrous anionic matrix composed of bacterial and algal glycocalyces. The theoretical ramifications of this demonstration of a complex epilithon, in the context of bacterial digestive processes, N cycling, metal sorption, and the flux of organic matter in the stream ecosystem are discussed in terms of a structural-functional hypothetical model of the epilithon.