Annual cycle of phytoplankton with emphasis on potentially harmful species in oyster beds of Términos Lagoon, southeastern Gulf of Mexico

To define the composition of the phytoplankton community, with an emphasis on harmful species, 6 stations were monitored monthly in the oyster beds of Términos Lagoon, SE Gulf of Mexico, from August 2012 to September 2013. Water temperature, salinity, hydrogen potential, oxygen saturation, inorganic nutrients and abundance of phytoplankton were determined. Temperature and salinity were characterized by marked seasonal differences. The pH values and the oxygen saturation suggest a predominance of photosynthetic activity. The phytoplankton community was characterized by the dominance of nanoflagellates and diatoms. The abundance and seasonal variation of phytoplankton showed minimum values (103 cells L^-1) during the dry season (February-May) and high values (106 cells L^-1) during the rainy season (June-September). Another significant feature of the phytoplankton community was the presence of the harmful dinoflagellate species Akashiwo sanguinea, Karenia cf. mikimotoi, Pyrodinium bahamense var. bahamense, Prorocentrum mexicanum and P. minimum. The cyanobacteria Anabaena and Cylindrospermopsis cuspis reached abundance of 1.9x106 and 1.3x106 cells L^-1, respectively. The genera Alexandrium and Pseudo-nitzschia were present, but the taxa were not identified to the species level. In conclusion, the phytoplankton community undergoes changes in both species composition and structure of the community during each climatic season, in response to environmental variation, which allows the development of the phytoplankton community according to the conditions.