Colonisation, competitive ability and influence of Stragulum bicolor van Ofwegen and Haddad, 2011 (Cnidaria, Anthozoa) on the fouling community in Paranaguá Bay, Southern Brazil

The octocoral Stragulum bicolor exhibits fast growth and frequently overgrows other invertebrates. This species has probably been introduced on the Brazilian coast. This study aims to evaluate the ability of S. bicolor to colonise previously occupied substrates and its influence on the fouling community throughout the successional process and to verify whether the community limits its growth. Experimental plates (15 × 15 cm) subjected to various treatments (cumulative control, cumulative with removal of S. bicolor, cumulative with removal of other species and non-cumulative) were submerged at 1-m depth for a period of 26 months in Paranaguá Bay in southern Brazil. The cumulative plates were photographed monthly, and the non-cumulative plates were recovered every two months and replaced with new ones. Species richness, diversity and evenness were compared between the control and experimental treatment without S. bicolor. The number of colonies, area and growth of S. bicolor were compared between the control and treatment without other species. Recruitment was compared among non-cumulative and without S. bicolor treatments. The effects of S. bicolor on species richness, diversity and evenness were sporadic. The community did not limit the area and growth of S. bicolor, and the number of colonies was higher on the control plates. Although the number of recruits was higher on non-cumulative plates in certain periods, the presence of an already developed community did not prevent recruitment. S. bicolor had no adverse effect on community development. However, this species was efficient in occupying both pre-colonised and clean substrates. It is important to monitor the population of S. bicolor in Paranaguá Bay because this species has probably been introduced in this region and has the potential to become invasive.