[en] Highlights: • The benthic community was affected by the growth and decline of Bo. proboscidea populations. • The boom-bust of Bo. proboscidea invasion was mediated by sewage. • In the boom of Bo. proboscidea was observed the species loss. • Bo. proboscidea and Br. rodriguezii coexist when decreased Bo. proboscidea population. • Community parameters decrease during the boom phase of Bo. proboscidea invasion. Biological invasions produce an invader population boom but are often followed by an invader population bust. The decrease of the invader abundance ends with the coexistence of native species and the invader or with repeated boom and bust events. In the southwest Atlantic, the polychaete Boccardia proboscidea invaded the coasts influenced by sewage discharge. We studied the change in the intertidal benthic community during the boom-bust dynamic of the Bo. proboscidea invasion. During the boom, the invader polychaete was dominant forming monoculture reefs. Species richness, diversity, and evenness indices decrease in the boom phase. During the bust of the Bo.proboscidea invasion, the decrease of organic matter allowed Br. rodriguezii to coexist with Bo. proboscidea. Beta diversity comparing boom with the bust phase showed a greater nesting (nestedness component); reflecting a process of species loss. We found that both boom and bust phases of the polychaete Bo. proboscidea invasion were mediated by sewage.