The effect of the invader Boccardia proboscidea (Polychaete: Spionidae) on the richness, diversity, and structure of the SW Atlantic rocky intertidal community

JAUBET MARÍA LOURDES; SÁNCHEZ MARÍA DE LOS ANGELES; LLANOS ELIZABETH NOEMÍ; VALLARINO EDUARDO ALBERTO; SANDRINI-NETO LEANDRO; ELÍAS RODOLFO

Punta del Este

Congreso; XV COLACMAR. Congreso Latinoamericano de Ciencias del Mar; 2013

In Mar del Plata (38º S, 57º W), a large resort by the sea, the intertidal untreated sewage discharges affect littoral ecosystem. Around the abrasion platforms of stony rocks affected by the sewage discharge a large, massive reef develops from spring of 2008. The reef is produced by an invader species Boccardia proboscidea, a not forming reef polychaete. The effect of this species on benthic macrofauna was assessed through an MBACI design in two sampling years, three times before and seven times after the arrival of the introduced polychaete, both in sewage-impacted and references sites. The ecosystem engineer bivalve, Brachidontes rodriguezii, declined due to both their inability to support high levels of organic sewage-induced contamination and B. proboscidea competition. Richness and diversity drops to almost zero in sewage impacted sites, because mussel beds were reduced. Despite these general patterns, analysis of variance and planned comparisons did not show a strong and consistent effect of B. proboscidea on associated benthic macrofaunal species. Patterns were strongly dominated by small-scale variability, due to occasional large peaks in abundance on a single sampling time and large variation among replicates. The ocurrence in high densities of the invasive polychaete acted differently at the smallest scales analyzed, so that variations from time to time were distinct within control and impacted sites. Formerly rich and diverse associate fauna, enriched in impacted sites due to the presence of opportunistic and tolerant species, were excluded because the monoculture of B. proboscidea.