Seasonal changes in the epiphyte community of natural and artificial macrophytes in Lake Memphremagog (Que. & Vt.)

Abstract

Seasonal changes in the epiphyte biomass, measured both as chlorophyll a and as cell volume, and species composition were compared on Potamogeton richardsonii and on a similar plastic plant ‘grown’ together in a shallow bay of Lake Memphremagog (46°06'N, 72°16′W). Both substrates exhibited two periods of high biomass during the June to September growing season; one in June, when the community was dominated by loosely attached species with a strong planktonic component (up to 37%), and one in September, when the epiphytes were characterized by species tightly attached to the leaves. Although this seasonal trend was similar, the loosely and tightly attached communities were best developed on the natural and artificial plants, respectively. The diversity of the epiphytes was significantly higher on the natural than on the artificial leaves from July on. Both the diversity differences and differences in community structure appear to be the result of the summer accumulation of CaCO3 observed only on the upper leaf surfaces of the natural plants. Consequently, P. richardsonii appears to affect epiphyte development largely by its precipitation of CaCO3, with no evidence for either direct inhibition or stimulation of the epiphytes by the natural plants. The reduced epiphyte biomass on growing tips was no different from that on artificial plants of the same age and exposure and is attributable to an insufficient time for colonization rather than to inhibition by the macrophyte.