Spatial and temporal variations of assemblages in a Mediterranean coralligenous reef and relationships with surface orientation

The structure, distribution, and temporal changes of epibenthic assemblages of a Mediterranean coralligenous reef were investigated using a multifactorial sampling design. The distribution of taxa on vertical walls and down-facing surfaces of overhangs and crevices was analysed at ten sites along 2 km of rocky reefs, south of Livorno (Ligurian Sea, Italy). The temporal variations were analysed between two periods (1995-1996 and 1997-1998) and among four sampling times within each period. Most of the space was dominated by prostrate seaweeds (including Peyssonnelia rubra, P. rosa-marina, and Mesophyllum lichenoides), turf-forming seaweeds, and the red coral Corallium rubrum. The cover of a variety of other invertebrates, mainly sponges and bryozoans, was less than 2%. All taxa were found on both vertical and down-facing surfaces. However, seaweeds dominated the vertical surfaces (mean cover > 97%), while C. rubrum and other invertebrates dominated down-facing surfaces (mean density of C. rubrum > 16 colonies dm(-2)). Although there was some fluctuation in the abundance of taxa, no obvious patterns were observed. These results support the model of limited temporal variability in Mediterranean coralligenous reefs, possibly related to the slow growth rates of the most abundant taxa and the reduced seasonality of physical conditions.