Limnoperna fortunei, an Asiatic rivers bivalve has become a worldwide problematic invasive species causing several water quality and macrofouling problems. In the Neotropical region it was first recorded in 1991 in the Río de la Plata coast, Buenos Aires province. Since this, it showed a quick upstream invasion into the principals aquatic systems of the Plata Basin. Nevertheless, there is not a study about its invasion and distribution process in aquatic systems of Uruguay. We describe the new records of Limnoperna fortunei in Uruguayan coast of Río de la Plata, Santa Lucía, Negro and Uruguay Rivers. With these results we aim to estimate its distributional limits for Uruguay main hydrographical basins. We also deal with the role of salinity as the main abiotic factor in limiting the east distribution of this mussel in Uruguayan coast of Río de la Plata and as a potential determinant of the "new" colonization on the Atlantic and the Merín Lagoon Basins. Its presence in the ecosystems not only can cause changes at the ecosystem level but also endanger the associated community, favoring the displacement and the disappearance of endemic species.

A study on sediment surface diatom composition in relation to both protein/carbohydrate content and salinity was carried out in Montevideo Bay and the adjacent coastal zone. Samples were seasonally taken during one year along a human impact gradient, and the trophic conditions were assessed from the biochemical composition of the surface sediment organic matter. The co-occurrence of the marine-brackish (Actinocyclus curvatulus, Actinocyclus gallicus, Coscinodiscus excentricus, Coscinodiscus radiatus, Hyalodiscus subtilis, Paralia sulcata) and freshwater diatom flora (Aulacoseira granulata, Aulacoseira italica, Aulacoseira muzzanensis, Actinocyclus normanii, Amphora copulata, Cyclotella meneghiniana, Nitzschia linearis), suggests myxohaline estuarine conditions in the study area. The sampling stations located within the bay, close to several contamination sources, exhibited hypertrophic conditions as indicated by the highest levels of protein content, but also by the high relative abundances of Actinocyclus normanii and Cyclotella meneghiniana, as both diatom species are very well established cosmopolitan proxies of aquatic degradation. The levels of both protein and carbohydrate content, but also photosynthetic pigments, recorded in the adjacent coastal zone suggest meso-eutrophic conditions as contamination levels from the inner bay might become diluted off shore. Multivariate diatom species-environmental data relationships, indicate that the trophic gradient is hierarchically more important than salinity in explaining the diatom distribution. The present data imply an improvement in our ability of assessing organic contamination in the study area, since both biological and biopolymer variables were introduced for the first time as a tool for assessing the benthic health/degradation in one of the most populated regions of the Río de la Plata.

In Uruguay, as well as in other regions of the world, IAS cause negative impacts on natural and managed ecosystems. The use of databases is a helpful tool to elaborate different strategies for prevention and control, and to develop policies and scientific analyses related to IAS. The database of IAS in Uruguay (InBUy) was developed during two time periods (2006-2007 and 2009-2010). It currently contains information on 33 specialists of different taxonomic groups, 14 research projects, 185 references, 351 species and 4,715 records, with vascular plants having both the highest number of species and records. Among vascular plants, herbaceous life forms are the most strongly represented, followed by trees and shrubs. Within animals, the fishes and mollusks are the most important groups. Analysis of the native distribution areas of IAS showed that most are indigenous from Europe, followed by Asia and Oceania. Data showed that introductions of IAS into Uruguay are mainly intentional (67%), so efforts should be focused on policies and rules in order to control the entrance of exotic organisms and prevent new invasions. The geography of the compiled dataset shows the main impact is along the coastline, where the highest exotic species richness and records occurs, and also the most biological invasions. The InBUy database is up-to-date and has successfully contributed to the creation of an official IAS list for Uruguay and both a National and a Coastal Geographic Information System. It has also been used for developing consciousness about this important threat to biodiversity, at both national and regional scales.