Spatial and seasonal changes of microphytoplankton community assemblages, including harmful species in Acapulco Bay, Mexico

The composition of marine phytoplankton communities and environmental factors influencing their dynamics establish the trophic state of coastal ecosystems. The spatial distribution of the microphytoplankton community in Acapulco Bay, Mexico, was determined during two climatic seasons (dry and rainy). Dinoflagellates constituted the dominant group of microphytoplankton, followed by diatoms in both seasons. There was low numerical diversity but maximum dominance associated with harmful algal bloom (HAB) taxa, such as the diatom Pseudonitzschia and the dinoflagellate Dinophysis - potential producers of amnesic- (AST) and diarrheic-shellfish toxins (DST), respectively. Higher maximum nutrient concentrations likely promoted dominance of HAB species during the rainy season. Community structure analysis revealed that temperature and nutrients, e.g., inorganic phosphate and nitrate/ammonium concentrations, were key factors in the proliferation of the dinoflagellates Dinophysis caudata during the dry season and Triadinium polyedricum during the rainy season. The seasonal assemblages of dominant microphytoplankton species and HAB-forming taxa constitute a historical reference and provide essential knowledge for decision-making on biodiversity stability in the face of climate change.