Ciclo anual del fitoplancton con énfasis en las especies potencialmente nocivas en bancos ostrícolas de la laguna de Términos, sureste del Golfo Resumen.-Para definir la composición de la comunidad fitoplanctónica con énfasis en las especies nocivas en los bancos ostrícolas de la laguna de Términos, SE del Golfo de México, 6 sitios de muestreo fueron monitoreados mensualmente desde agosto 2012 a septiembre 2013. Se midió la temperatura del agua, salinidad, potencial de hidró geno, saturación de oxígeno, nutrientes inorgánicos y la abundancia de fitoplancton. La temperatura y la salinidad se caracterizaron por diferencias estacionales marcadas. Los valores de pH y saturación de oxígeno sugirieron un predominio de la actividad fotosintética. La comunidad fitoplanctónica se caracter izó por el predominio de nanoflagelados y dia tomeas. La abundancia de fitoplancton y su variación estacional presentaron los valores mínimos (10 3 células L -1 ) durante la época de secas (febrero-mayo) y valores al tos (10 6 célul as L -1 ) dur ante la temporada de lluvias (junio-septiembre). Otra característica importante de la comunidad fitoplanctónica fue la presencia de especies de dinoflagel ados nocivos: Akashiwo sanguinea, Karenia cf. mikimotoi, Pyrodinium bahamense var. bahamense, Prorocentrum mexicanum y P. minimum. Las cianobacterias Anabaena y Cylindrospermopsis cuspis alcanzaron abundancias de 1.9x10 6 y 1.3x10 6 células L -1 , respecti vamente. Los g éneros Alexandrium y Pseudo-ni tzschia estuvi eron presentes, pero los taxones no fueron identificados a nivel de especie. En conclusión, la comunidad fitoplanctónica se somete a cambios en la composición de especies y en la estructura de la comunidad durante cada temporada climática, en respuesta a la variación ambiental, que permite el desarrollo de la comunidad fitoplanctónica de acuerdo a las condiciones imperantes. Palabras clave: Cambios estacionales, cianobacterias, diatomeas, dinoflagelados, lagunas costerasAbstract.-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. , 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. Key words: Seasonal changes, cyanobacteria,...

No abstract

Cyanobacteria inhabit hypersaline, marine and freshwater environments. Some toxic and non-toxic species can form harmful blooms. The aim of this study was to identify potentially harmful cyanobacterial species in the oyster banks of Términos Lagoon, the southeastern Gulf of Mexico. Six sample sites (up to 2-m depth) were monitored monthly from August 2012 to September 2013. Water temperature, salinity, pH, dissolved oxygen saturation (% DO), inorganic nutrients and abundance of cyanobacteria were determined. Temperature and salinity were characterized by marked seasonal differences (26.8 to 30.6 °C and 6.1 to 19.5, respectively). The pH values (ranging from 7.1 to 8.4) and the % DO (88.4 to 118.2 %) suggest a predominance of photosynthetic activity in the windy season (October-February). Elevated nutrient contents are associated with the period of increased river discharge, determined by water circulation and biogeochemical processes. Fourteen taxa were identified, of which Anabaena sp., Merismopedia sp., Oscillatoria sp. and Cylindrospermopsis cuspis produced blooms. Cyanobacterial abundances were on the order of magnitude of 10 6 cells L -1 in October 2012 at stations S1-S6, with an average value of 3.2x10 5 cells L -1 and a range of 2000 to 3.1x10 6 cells L -1 throughout the study period; however, they showed a remarkable absence during the windy season (October to January). Anabaena sp. and C. cuspis reached abundances of 1.9x10 6 and 1.3x10 6 cells L -1, respectively. The latter caused the temporary closure of oyster Crassostrea virginica harvesting for 15 days in October 2012.