A Review of the Intertidal Rocky Shore Community at Mar del Plata (Argentina) Characterized by the Mussel Brachidontes rodriguezii (d’ Orbigny, 1846)

In the rocky shores of Mar del Plata (38°W 04’S), intertidal mussels monopolize the macrofauna communities developing beds dominated by the small mytilid Brachidontes rodriguezii. This species covers 45% to 65% of the mid and upper mid intertidal substrate forming stratified beds. Vertical protected substrates of the midlittoral show the highest densities of B. rodriguezii, up to 175,000 indiv. m-2 representing a dry biomass of 1,670 g. m-2; upper horizontal substrates at the same level show lower densities (80,000 indiv. m-2; 592 g. m-2). The horizontal bed matrix accumulates more sand than vertical beds (19.1kg. m-2 and 5.1kg. m-2, respectively). Twenty-six taxa and 14 animal species were recorded within the B. rodriguezii intertidal matrix while a total of 9 algae species were found living on the mussel bed. The pulmonate limpet Siphonaria lessoni is the main intertidal herbivore. The invasive barnacle species, Balanus glandula, was first detected in Mar del Plata in 1974 and today creates an upper midlittoral fringe at densities up to 5,000 indiv.m-2. This review of the Mar del Plata rocky shore community summarizes the existing information as we prepare to sample this area with the NaGISA protocols. The uniqueness of the rocky intertidal of Mar del Plata is the absolute dominance of a single mussel species Brachidontes rodriguezii in the midlittoral, the presence of a sole species of Gastropoda, the grazer pulmonate Siphonaria lessoni and the absence, until the mid sixties, of a barnacle belt.