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ABSTRACT1. Biological invasions have had severe impacts on ecosystems globally, particularly affecting freshwater habitats. In the aquatic realm, marine environments have received less attention from researchers than their freshwater counterparts, and comparisons of the relative susceptibility of coastal and inland waters to alien species and their consequential impacts are lacking.2. The main aim of this review is to assess the 'knowns and unknowns' for alien species in aquatic habitats, evaluating the possible differences and similarities in biological invasions between freshwater and marine (coastal) environments. Three study areas with different climates and histories of bioinvasion were selected for comparison: temperate Europe, tropical Asian Hong Kong, and Neotropical Brazil.3. Although there were differences in spatial scale and availability of data for the three areas, fresh waters seemed to be more susceptible to invasion -and experienced more impacts -than coastal habitats, at least in Hong Kong and partly in Europe. Despite information about alien species in aquatic environments having increased in recent years, regional inventories remain incomplete, especially in the tropics where rigorous studies of the impacts of invasive species are generally lacking.4. More systematic effort is needed to develop up-to-date national and regional inventories of invaders, especially in the seas and particularly in the more biodiverse tropics, where the conservation gains from preventing alien invasions could be substantially greater than in other regions. Greater efforts are also required to increase public awareness of the need to prevent the establishment of potentially invasive species.

Despite limited natural dispersal, some species of ascidians can be transported vast distances via oceanic petroleum platforms, ship hulls and ballast 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 degradation 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 opportunity 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 introduced 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 population growth of the already known species. Management to reduce the transfer of exotics to natural habitats must be implemented

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BackgroundBiological invasions are a major cause of global species change. Nevertheless, knowledge about the distribution and ecology of introduced species is regionally biased, and many gaps in knowledge exist for most developing countries.Methodology/Principal FindingsTo study the zoobenthos on the hard substratum of the Ilha Grande Bay, a survey was conducted on both natural and artificial substrata at three depths and seven sites. The species recorded were classified as native, cryptogenic or introduced. Multivariate analyses were conducted to assess the prevalence of introduced species in these communities and to compare the distribution of species on natural and artificial substrata of this bay to identify possible discrepancies in habitat use. Of the 61 species, 25 were cryptogenic, 10 were introduced and 26 were native. Similar numbers of introduced species were found on both natural and artificial substrata, though the community composition was significantly different between them. We also compared the species composition of the Ilha Grande Bay survey to other inventories taken around the world. The highest similarities were found between the Ilha Grande Bay inventory and the Atlantic coastal region (Tampa Bay, USA and the Gulf of Mexico), American Samoa and Pearl Harbor (USA) inventories.Conclusions/SignificanceThis study presents the first published comprehensive list of hard substratum sessile marine invertebrate species in a Brazilian bay. The high percentage of cryptogenic species reveals gaps in both zoological records and information on introduced species for the Brazilian coast. The introduced species successfully colonized different sites in the Ilha Grande Bay, including both natural and artificial substrata. In addition, we find that artificial structures may not be good surrogates for natural rocky shores and may represent an ecological threat. Comparisons with other inventories suggest a history of broad-scale invasion, though more evidence is needed to support this conclusion.