Morpho-Molecular and Ecological Characterization of Potentially Toxigenic Epiphytic Dinoflagellates from the Southeastern Mexican Pacific

Potentially toxigenic epiphytic dinoflagellates represent an emerging risk to marine ecosystems and public health. This study characterized the spatio-seasonal dynamics, relationship with environmental factors, substrate preferences, and morpho-molecular identity of the epiphytic dinoflagellate community from the southeastern Mexican Pacific. The community was estimated from various dominant macroalgal genera. Sampling was conducted during the rainy (October 2022) and dry (April 2023) seasons in three coastal areas of Acapulco, Mexico. An integrative approach was used, combining advanced microscopy techniques with molecular analyses using the ITS1-5.8S-ITS2 and 28S LSU regions of rDNA. Five genera of epiphytic dinoflagellates were identified: Amphidinium, Prorocentrum, Ostreopsis, Coolia, and Gambierdiscus. The genera Amphidinium and Prorocentrum dominated the community and showed generalist substrate preferences, with greater abundance during the rainy season, while Gambierdiscus, Ostreopsis, and Coolia reached their highest abundances during the dry season and specialized in association with macroalgae of the genera Centroceras and Ulva. Temperature, salinity, and inorganic nutrients regulated the abundance of these taxa by season. Molecular analyses using 28 monoclonal cultures identified nine dinoflagellate species: Amphidinium operculatum, A. tomasii, A. fijiensis, A. carterae, A. thermaeum, Prorocentrum rhathymum, P. lima, Coolia palmyrensis, and Gambierdiscus carpenteri. These findings constitute the first integrated record of toxigenic epiphytic dinoflagellates in the southeastern Mexican Pacific.