Mytilopsis leucophaeata naturally occurs in oligo- to mesohaline estuaries along the Atlantic coast of the USA and Mexico. In Brazil, M. leucophaeata was first recorded in 2004 in estuaries adjacent to the Port of Recife (Pernambuco State, north-eastern Brazil). Here, we present the second record of the species in Brazil, and the first for the south-eastern region, in the Rodrigo de Freitas lagoon (Rio de Janeiro State). This lagoon, located within a major urbanized area of Rio de Janeiro City, is highly affected by coastal development, but used for various nautical sports. The imminence of the Olympic Games, to be held in Rio de Janeiro in 2016, requires specific attention to the importance of monitoring and controlling this new invasive species. Action has to be taken to prevent its dispersal to other estuarine and lagoon ecosystems of Rio de Janeiro State due to movement of boats and sport equipment.
