Spatial distribution of medusae (Cnidaria) assemblages in the southern Gulf of Mexico (dry season)

The present study described the spatial patterns of the medusae assemblages in the southern Gulf of Mexico during the dry season of 2016 (May–June). The assemblages, defined based on Bray–Curtis similarity index, were described in terms of species composition, abundances, diversity, dominance, and the hydro-biological characterization of each of them. A total of 42 species were identified (40 Hydrozoa and 2 Scyphozoa), of which, 21.43% correspond to holoplanktonic specimens and 78.57% were meroplanktonic. The hydromedusae species Aglaura hemistoma (Trachymedusae) and Liriope tetraphylla (Limnomedusae) were the most frequent and abundant, accounting for 63.51% of the total abundances. Three groups of sampling stations with faunal affinity were identified, which showed different hydrological intervals and abundances of zooplankton groups (food availability), suggesting the existence of three communities composed of medusae species with affinity to the environmental parameters of each assemblage. With this regional characterization, A. hemistoma was the dominant species in the Yucatán shelf, L. tetraphylla in southern Campeche Bank, while L. tetraphylla and Nausithoe punctata (Coronatae) were dominant in the Veracruz shelf and the oceanic zone of the study area. The dominance of L. tetraphylla and A. hemistoma can be understood as the result of different adaptive aspects, such as the plasticity of the holoplanktonic condition of these species, the different feeding strategies, and trophic spectrum, which allows them to adapt to environmental variability in each one of these regions (e.g., high temperatures, salinities) and feed of a particular food source without competing among them.