Periodicity of epiphytes on Zostera marina in two embayments of the southern Gulf of St. Lawrence

Growing and cast leaves of Zostera marina were sampled from May through December and in February in two embayments of the southern Gulf of St. Lawrence to determine the species composition and temporal pattern of macroalgal epiphytes. Thirty-eight species were identified. Some occurred sporadically on Zostera while being present on other substrata throughout all or most of the growing season; other species were ephemeral, being discernible for only 1-3 months. A number of species overwintered on cast leaves. Four epiphtes, Eudesme, Desmotrichum undulatum, Leathesia difformis (all Phaeophyta), and Rhodophysema georgii (Rhodophyta) were studied in culture. The phenological patterns of these four species appeared to be governed by water temperature rather than day length.