Distribuição e composição taxonômica da classe Ascidiacea em águas rasas em uma zona de transição do litoral brasileiro, Atlântico Sudoeste

Abstract

Ascidians are exclusively marine, benthic, and sessile organisms found along coastlines worldwide in solitary or colonial forms. These organisms are considered excellent models for biogeographical studies due to their naturally limited distribution caused by the short-lived nature of their lecithotrophic larvae. This study investigated 20 locations along the Brazilian coastline, from Baía da Ilha Grande, RJ, to Parque Marinho Recife de Fora, BA, characterized as a Transition Zone between the Tropical Atlantic and Warm Temperate Atlantic biogeographic provinces. Dividing this stretch into four areas, Baía da Ilha Grande, Baixada Litorânea, Espírito Santo, and Southern Bahia, five collections were conducted in different localities. We identified 72 taxa, comprising 16 native, 24 exotic, and 17 cryptogenic species, besides 15 that were only classified at the genus level. Additionally, public and university databases were used to expand the distribution area of the species found in this transition zone to the entire Western Atlantic. Analyses revealed that exotic species increase local diversity but make areas with higher maritime activity more similar. Native species exhibit greater similarity in species composition between contiguous areas. When extended to the Western Atlantic, exotic species homogenize regions, while native species highlight the difference between the Brazilian coastline and the eastern US. This study emphasizes the need for a better understanding of the ecology, physiology, and interactions of ascidian species to comprehend their distribution and zones of endemism, as well as to monitor introductions and their impacts on benthic communities. Moreover, the results underscore the absence of distinct groupings of ascidian species within the established bioregions for the Brazilian coastline.