Non indigenous ascidians in port and natural environments in a tropical Brazilian bay

Abstract

Despite limited natural dispersal, some species of ascidians can be transported vast distances via oceanic petroleum platforms, ship hulls and allast water and therefore may be good indicators of bioinvasion. Usually non indigenous species (NIS) are abundant in harbors. This is caused in part because of the higher propagule delivery rate in these areas. An alternative explanation of why invasion is enhanced in harbor and marinas is that environmental degra-dation commonly found in these habitats favors the establishment of NIS. Most surveys for introduced species were not comprehensive and targeted mainly ports and marinas. Angra dos Reis is an excellent system that provides an opportu-nity to compare the potential distribution of introduced and native species of Ascidiacea between port and natural environments. Here, we compared the colonization of experimental subtidal plates placed in harbors and marinas with the colonization of plates placed in nearby natural areas. With 27 taxa (15 identified to species), species richness was greater in port environments (25 versus 8). Six taxa were common to both environments while 19 taxa were exclusively found in ports. Among the identified species in ports, three were introduced, five were cryptogenic and only one was native. Only three species were found exclusively in the natural sites and all were cryptogenic. The presence of intro-duced species only in the port areas of Angra dos Reis reinforces the need for continued, periodic monitoring in the region for early detection of new, potentially invasive, species as well as for better understanding of abnormal popula-tion growth of the already known species. Management to reduce the transfer of exotics to natural habitats must be implemented. © 2010 Sociedade Brasileira de Zoologia.