Factors Affecting the Distribution of a Freshwater Sponge

The distribution of Ephydatia fluviaatilis was considered at three habitat levels: lakewide distribution, littoral vertical distribution and rock surface preference. Lake-wide distribution was correlated with substrate type and the size and consistency of matrix particle composition. Exposure, ice scouring, silt accumulation and possible negative interactions with algae apparently affected the upper limits of the littoral vertical distribution. The lower limits were correlated with the adverse impact of silt abundance on sponge colony filtering capacity and larval settlement. Rock substrate found in water deeper than approximately 1.5 m maintained a relatively nonfluctuating, stable portion of the sponge population. At the third habitat level, rock surface preference, silt accumulation and possible harmful biotic interactions apparently caused the sponge to colonize the vertical and bottom surfaces of rubble.