El agua que los navíos embarcan como lastre cuando deben atravesar el océano sin carga suele contener organismos vivos. Al ser descargada aquella, estos ingresan en un medio al que son ajenos y pueden convertirse en plagas y en muchos casos originan serios trastornos ambientales. Los organismos descargados son especies exóticas. Se muestra un estudio en 5 puertos argentinos (océano Atlántico sudoccidental), formas de mitigar los trastornos y el estado de la situación actual de la problemática, con lecturas sugeridas. | Reprinted as: pp.161-166 in, Ciencia del Mar. Volumen temático 1, 12/2014; Asociación Ciencia Hoy. ISBN: 978-987-45584-0-4 (Special issue dedicated to 'Marine Sciences: 1988-2014')

Uruguay has a dense hydrographic network, nevertheless the knowledge of the aquatic macroinvertebrate community is still lacking. In recent decades afforestation with exotic species has increased which has produced changes in riparian vegetation of some rivers. The aim of this research was to determine the composition and trophic structure of macroinvertebrate community and its relationship to some physicochemical parameters in eight streams where the native forest is still well preserved and provide the basis for future studies. Samples were collected from December 2006 to December 2007. Temperature, dissolved oxygen, pH and conductivity were measured in situ. Taxonomic composition and abundance were determined, a principal component analysis and a canonical correspondence analysis were carried out with the physico-chemical and biological parameters. The alpha diversity was calculated using the Shannon-Weaver (H'), dominance of Simpson (D) and Pielou evenness indexes (J'). Beta diversity was determined employing similarity index of Bray-Curtis. A total of 1 291 specimens belonging 92 taxa were recorded. The most abundant taxa were Ephemeroptera (36%), Amphipoda (17%) and Coleoptera (12%). The streams show high diversity and low dominance. Conductivity, pH, and temperature were the main factors in determining the macroinvertebrate distribution and composition.

Information is presented about the prey consumed by the two-stripped garter snake Thamnophis hammondii in a mountain oasis in Baja California Sur, Mexico. The diet of this threatened snake includes the Baja California treefrog Pseudacris hypochondriaca curta (native species), as well as an exotic fish: the red bellied tilapia Tilapia sp. cf. zilli. This exotic species has become invasive in Baja California Sur oases, displacing native fishes and becoming an important dietary resource to T. hammondii.