Seasonal and depth-related distributions of epiphytic Bryozoa in a Mediterranean seagrass meadow

Although biofouling on Posidonia oceanica (L.) Delile is thought to be driven by the variability of environmental parameters and phenology of the plant, effect of these parameters on sessile animal colonization is still poorly understood. This study aims to document the seasonality and the bathymetric variability of epiphytic Bryozoa diversity and abundance on this seagrass Posidonia shoots were collected in the Revellata bay (Corsica, Mediterranean) in five seasons from 7 to 30 m depth. Colony densities may reach more than 87000 colonies. m-2 at 10 m depth in spring; this probably implies an important contribution of Bryozoa larvae to spring plankton where P. oceanica meadows are present. The Bryozoa specific distribution and abundance appeared to be determined by the seasonality of both the environmental parameters and the plant phenology. However, depth and associated environmental gradients played a structuring role. Based on our data and on the literature, we propose a classification of epiphytic Bryozoa in four categories from hyper-epiphytic specialist to accidental epiphytes and underline the necessity to protect seagrass systems on their full depth range to maximize biodiversity conservation.