Gammarid and corophiid amphipods were collected in Laguna de Tamiahua and Laguna Madre from seagrass beds, macroalgae, and bare substrates with a Renfro beam net and an otter trawl. Tamiahua provided 17 species, of which Cymadusa compta was the dominant species (66.3%), while Madre provided 24 species with C. compta (60.8%) and Elasmopus levis (20.2%) as the dominant species. Amphipod distribution was widespread in both lagoons, though concentrated along the inner margin of the sand barriers in Halodule wrightii beds. In Tamiahua, five species were present throughout the lagoon, E. levis in the north and center, Ampelisca vadorum in the north and south, and Nototropis minikoi and Melita nitida in the center and south, with Ampithoe valida only in the north, Ampithoe longimana only in the center, and Apohyale prevostii only in the south. In Madre, eight species were present throughout the lagoon, Gammarus mucronatus only in the north and south, Ampelisca vadorum only in the center and Catán, four species only in the north, two only in the center, and two only in the south. The number of species recorded in August and December in general did not vary, whereas the greater density values of August suggest optimum conditions for reproduction and survival, and the lower values of December may follow the harsher climatic conditions and/or predation by visiting migratory birds and fish that winter in these lagoons. Compared with Términos, Alvarado and each other, Tamiahua and Madre are the most similar, since they share 12 species, environmental characteristics, and seagrass distribution.
