Globalization and climate change have facilitated the establishment of non-indigenous species all over the world. Six non-indigenous species have been identified in the Guadiana estuary after the finalization of the Alqueva dam in 2002: the freshwater hydroid Cordylophora caspia, the black sea jellyfish Blackfordia virginica, the isopod Synidotea laticauda, the Atlantic blue crab Callinectes sapidus, the Oriental shrimp Palaemon macrodactylus and the weakfish Cynoscion regalis. In this work, the complex topology of the food web network of the Guadiana estuary was modelled in two ecological contexts, before and after the introduction of non-indigenous species. Properties of both networks were compared, with no important change being detected. Nevertheless, three of the new species are high generalists, meaning they play an important predatory role in the ecosystem. C. sapidus and P.macrodactylus are among the most highly-connected species in the network, thus playing an important role as both predators and prey. The network properties of the Guadiana estuary reveal that its web topology is more similar to that of small intermittent estuaries than that of large open estuaries. Its high connectance is likely to make it robust to impacts. Notwithstanding, monitoring plans should be implemented to prevent negative impacts by these non-indigenous species.
