Epífitos de las hojas de Posidonia oceanica: variaciones estacionales y batimétricas de biomasa en la pradera de las islas Medes (Girona)

Biomass seasonal variation of leaf epiphytcs of Posidonia oceanica along a depth gradient in Medes Islands (NE Spain). Biomass seasonal variation of the epiphytes of the mediterranean seagrass Posidonia oceanica was studied by means of a bi-weekly sampling program. Maxima, up to 0.5 gdw/shoot (270 gdw/m² of sea bottom) are evident in summer all along the depth gradient. A second maximum, in spring, is detected in the shallower stations. The former corresponds lo the encrusting Rhodophyta-dominated community, while the latter corresponds to another assemblage dominated by Phaeophyta. The relation between epiphyte biomass and sorne biological features of Posidonia was statistical1y investigaled. From a multiple linear regression model, it is concluded that the summer community is the endpoint of a succesion interrupted by leaf fall in early autumn, while the spring one is rather photophilic and represents a seasonal aspect of the community.