Seasonal and bathymetric variations of epiphytic macroflora on Posidonia oceanica (L.) Delile leaves in the National Marine Park of Zakynthos (Greece)

A survey on the epiphytic macroalgae growing on Posidonia oceanica leaves was conducted along a depth transect in Laganas Bay (National Marine Park of Zakynthos, Greece). Samples were collected using scuba diving at depths of 5, 10 and 15 m in July 2001 and January 2002. The meadow's density was measured at each depth and shoots were collected to examine and/or calculate: number of leaves per shoot, leaf surface per shoot, Leaf Area Index (m(2).m(-2)), number of epiphytic taxa and their coverage. Meadow density decreased at deeper sampling sites. Total leaf number was relatively constant at different depths in both summer and winter. Maximum leaf surface per shoot occurred at 15 m for both sampling periods. Leaf Area Index decreased from shallow to deep stations because of the decrease in the meadow's density. Concerning the epiphytic macroflora, a total of 30 taxa, at specific and infraspecific rank, were identified. Filamentous and crustose macroalgae were abundant in summer, and crustose forms dominant in winter. The number and coverage of identified macroalgae varied between seasons, with higher values being observed during summer. Macroalgae taxa and coverage decreased from the shallowest to the deepest station during both seasons. The present study shows that many parameters play an essential role in epiphytes settling, among them leaf features, depth, and light intensity.