RESUMEN
The aim of this study was to investigate the presence of alien phytoplankton species transported through ballast water of ships that docked on the Amazon coast. Phytoplankton samples were collected from 25 ships between 2012 and 2014, revealing 215 identified species, mostly comprising oceanic planktonic marine species. However, several coastal and freshwater species not yet documented on the Maranhão coast were also observed. The identification of several coastal and freshwater species not yet recorded for Amazonian environments in the ballast water of the Ponta da Madeira Maritime Terminal (TMPM), as well as toxic microalgae genera such as the dinoflagellates Alexandrium and Gymnodinium and of some diatom species from the genus Pseudo-nitzchia, raises concerns regarding the possibility of introducing species. This indicates that ballast water can be responsible for the introduction of alien species in Amazonian aquatic environments, thereby highlighting the TMPM as a critical hotspot in the Amazonian region.