RESUMO
Bivalves are one of the most representative groups in the Phylum Mollusca, with over 1,100 freshwater species around the world except Antarctica. About 900 of these species belong to the Order Unionida Gray, 1854. In South America, the distributional range of the Unionida includes all countries in the region and extends as far south as the lakes and rivers of Argentinean-Chilean Patagonia. With the aim of generating distribution maps for the different genera of Unionida in Argentina, we consulted the databases of the nation's main official malacological collections. The data were analyzed and georeferenced using the point-radius method. Spatial analyses were performed with the software Q-GIS 2.16.3 Nødebo using vector layers under the 2007 Argentinean Geodesic Positions reference system. A total 1,833 lots were analyzed, of which it was possible to georeference 1,503. The distribution of Unionida in Argentinean territory was analyzed according to political provinces, Surface Drainage Basins and the Argentinean Protected Areas. Species richness was analyzed using the surface drainage basins of Argentina. We generate distribution maps for each genus and discuss the species threat status and conservation degree in the region. Only six (18%) of the Unionida present in Argentina have been classified by the IUCN, four are Least Concern and two are Data Deficient. This pattern is also valid for all of South America. More than 95% of the distributional range of the Unionida has no protected area. Conservation management is necessary for the preservation of Unionida diversity in southern South America.
Assuntos
Bivalves/classificação , Animais , Argentina , Biodiversidade , Conservação dos Recursos Naturais , Água DoceRESUMO
In 1981, Corbicula fluminea (Müller, 1774) and C. largillierti (Philippi, 1844) were recorded at the Río de la Plata River. During the 1980s, C. largillierti was found on a continuous fringe in the shore of that river, while C. fluminea was only found North of Buenos Aires harbor. Ten years later, C. fluminea spread to Punta Indio, while C. largillierti remained restricted to tributary streams. The density and size frequency distribution of both species were compared with previous data from samples performed in the same area in 1985-1989. The aim of this research was to determine whether the densities of both species decreased; whether C. fluminea is still more abundant than C. largillierti; and whether the size frequency distributions indicate different population structures from those observed in the end of the 1980s. Nine localities from the river shore were sampled, and each individual was identified and measured. The size of C. fluminea varied between 2 and 39 mm, showing the highest frequency of individuals between 20 and 25 mm; furthermore the density decreased 90% in 2015/2016. No specimens of C. largillierti were found. In conclusion, the populations of Corbicula inhabiting the Río de la Plata River are retracting.
Assuntos
Animais , Corbicula/anatomia & histologia , Espécies Introduzidas , Distribuição Animal , Distribuição TemporalRESUMO
In 1981, Corbicula fluminea (Müller, 1774) and C. largillierti (Philippi, 1844) were recorded at the Río de la Plata River. During the 1980s, C. largillierti was found on a continuous fringe in the shore of that river, while C. fluminea was only found North of Buenos Aires harbor. Ten years later, C. fluminea spread to Punta Indio, while C. largillierti remained restricted to tributary streams. The density and size frequency distribution of both species were compared with previous data from samples performed in the same area in 1985-1989. The aim of this research was to determine whether the densities of both species decreased; whether C. fluminea is still more abundant than C. largillierti; and whether the size frequency distributions indicate different population structures from those observed in the end of the 1980s. Nine localities from the river shore were sampled, and each individual was identified and measured. The size of C. fluminea varied between 2 and 39 mm, showing the highest frequency of individuals between 20 and 25 mm; furthermore the density decreased 90% in 2015/2016. No specimens of C. largillierti were found. In conclusion, the populations of Corbicula inhabiting the Río de la Plata River are retracting.(AU)