Until the late 2010s, the spiny fan-mussel Pinna rudis shared its habitat in many Mediterranean sites with the Mediterranean endemic Pinna nobilis, which used to be dominant, but has recently become locally extinct in most of its distribution areas due to a widespread disease outbreak. In the Columbretes Islands Marine Reserve (NW Mediterranean), both species coexisted until 2017, when P. nobilis populations completely disappeared. In spring 2021, we revisited seven permanent plots covering 1,485 m2 that had been previously monitored from 2005 to 2009. We found that although previous studies have described P. rudis populations as stable with low recruitment rates, recruitment increased after 2017 in comparison to 2005-2009. At least two cohorts of recruits (~3 and ~1 year in age, respectively) were found in the plots as well as in other areas throughout the Columbretes archipelago, colonizing areas previously occupied by P. nobilis. We hypothesize that P. rudis has benefited from the local extinction of P. no bilis, most probably as a result of reduced interspecific competition. The ecological role once played mainly by P. nobilis as the dominant species might now be played by P. rudis, whose populations could grow in the coming years.