STRUCTURE, SEASONAL DYNAMICS AND REPRODUCTIVE PHENOLOGY OF A FILAMENTOUS TURF ASSEMBLAGE ON A SEDIMENT INFLUENCED, ROCKY SUBTIDAL SHORE

Seasonality and reproductive phenology of marine macroalgae were investigated from June 1992 to June 1993 on a subtidal rocky shore south of Livorno (Western Mediterranean Sea) that was characterized by high rates of sediment deposition and movement. The assemblage was strongly dominated by a persistent filamentous turf of Polysiphonia setacea that covered the rocks and encrusting algae, while Halimeda tuna was the only abundant erect species. During the year the thickness of the turf fluctuated in response to changes in weather conditions and in the intensity of depositional environment. Conversely, the composition and the structure of the assemblage remained rather constant, and its diversity was quite low. It is suggested that both sediment stress and competitive interactions among P. setacea and erect species might play an important role in maintaining and structuring the algal turf in the study area.