Primer registro de Cloeon dipterum (L.) (Ephemeroptera: Baetidae) en Buenos Aires, Argentina RESUMEN. Cloeon dipterum (L.) (Ephemeroptera: Baetidae) está ampliamente distribuido en las zonas templadas de Eurasia, sin embargo, está restringido en América del Norte a tres estados de Estados Unidos y Canadá, y en América del Sur a Chile. Con el fin de confirmar nuestra hipótesis de que se introdujo recientemente en Argentina, el objetivo del presente estudio fue identificar la especie en base a análisis moleculares y caracteres morfológicos. Para ello se recolectaron ninfas de tres hábitats artificiales en diferentes localidades de la provincia de Buenos Aires y de dos arroyos afluentes del Río Luján, al noreste de Buenos Aires (Argentina). Todas las ninfas fueron identificadas como C. dipterum, lo que confirma la presencia de la especie en Argentina. La distribución de C. dipterum en Buenos Aires junto a su ausencia en los sitios previamente muestreados de manera regular, indicarían que los individuos registrados son introducidos y están bien establecidos en la zona de estudio. PALABRAS CLAVE. Cuerpos de agua neotropicales. Especie exótica. Insectos acuáticos. ABSTRACT. Cloeon dipterum (L.) (Ephemeroptera: Baetidae) is widely distributed in temperate areas of Eurasia, whereas, in North America, it is restricted to three states of the USA and Canada, and, in South America to Chile. To confirm our hypothesis that C. dipterum has been recently introduced in Argentina, the aim of the present study was to identify the species based on molecular analyses and morphological features. To this end, nymphs were collected from three artificial habitats located in different localities of Buenos Aires province and two tributary streams of the Luján River, northeast of Buenos Aires, Argentina. Nymphs were all identified as belonging to C. dipterum thus confirming the presence of the species in Argentina. The distribution of C. dipterum in Buenos Aires, together with its absence from previously sampled sites, would indicate that the individuals recorded are introduced and already well established in the study area.

The increase of urbanized areas produces disturbances in rivers and streams, and its widespread effects reduce water quality and threaten aquatic biota. The aim of this study was to analyze changes in the invertebrate communities of the Luján River basin (Buenos Aires Province, Argentina) in an urbanization gradient and to determine the specific indicator taxa of urbanized habitats. Nine sampling sites were selected in the Luján River basin, distributed along a land use gradient. At each sampling site physicochemical variables of water were recorded, and invertebrate samples were collected during four seasons. A Principal Component Analysis separated three groups of sites with different urbanization conditions: low (<15%), moderate (between 15% and 60%) and high urbanization (>60%). These groups showed differences in the concentration of dissolved oxygen, suspended particulate organic matter, and nitrates. The communities changed with urbanization conditions, with a simplification of the community composition and a decrease in richness towards the lower basin (moderate and high urbanization). The IndVal method found three indicator taxa for the low urbanization sites (Heleobia sp. (Cochliopidae), Uncancylus sp. (Ancylidae) and Callibaetis sp. (Baetidae)) and three for the moderate urbanization habitats (Nematoda, Hyalella curvispina (Hyalellidae) and Chironominae). These taxa were useful to identify different disturbance conditions due to urbanization, which makes them potential bioindicators in the diagnosis and monitoring of water quality in the Luján River basin.