Macrophyte and associated mollusc communities in a meteor crater lake on the Precambrian Shield in Manitoba

Abstract

Submerged macrophyte and associated mollusc communities were investigated in West Hawk Lake, a cold deep meteor crater lake on the Precambrian Shield. Despite good light penetration, macrophytes grew no deeper than 8.5 m, and temperature was probably a major limiting factor. The nine macrophyte taxa showed low biomass and marked vertical zonation, with Chara globularis dominating the communities in the lower half of the macrophyate zone. Macrophyte species richness decreased with increasing depth. Ten gastropod species were associated at low densities with the macrophytes. Valvata sincera was significantly more abundant at depths of more than 5 m. The species mentioned are Zosterella dubia, Eleocharis sp., Nitella sp., Potamogeton amplifolius, P. epihydrus, P. gramineus, P. ichardsonii, P. robbinsii, Valvata tricarinata, Amnicola limosa A. walkeri, Gyraulus deflectus, G. parvus, Promenetus exacuous, Helisoma anceps royalense, Fossaria exigua and Physa gyrina