The role of Didemnum perlucidum F. Monniot, 1983 (Tunicata, Ascidiacea) in a marine fouling community

Didemnum perlucidum is a colonial ascidian that is cryptogenic in southern Brazil but introduced in many regions around the world. It is common in ports and marinas where it may form large colonies although its role in fouling communities is poorly understood. The goal of this study was to evaluate the role of D. perlucidum in a marine fouling community comprised mainly of non-indigenous species. Treatment pairs (D. perlucidum removal and unmanipulated controls) of experimental plates were exposed during 14 months at a mussel farm in southern Brazil. Taxonomic richness and percent cover of the species were compared between treatments (with and without D. perlucidum). D. perlucidum did not influence taxonomic richness or inhibit colonization by any species. Effects of this species on the abundance of others were sporadic, and suggest that it may be a weak competitor. The small effect of D. perlucidum in this community is explained by its low abundance and its occupation of secondary substrate without having detrimental effects on the species it grew over. Given that D. perlucidum is more abundant, and problematic, in other regions of southeastern and southern Brazil, continuous monitoring is desirable to better understand its