Co-ocurrence of two toxic dinoflagellates in Acapulco Bay, Guerrero, Mexico: an opportunity to quantify their biology and ecology

Abstract: Background and Aims: Harmful Algal Blooms (HAB) commonly occur in the Mexican Pacific, being important HABs of Gymnodinium catenatum (Gc) and of Pyrodinium bahamense var. compressum (Pbc) for being saxitoxin-producing dinoflagellates that cause paralytic shellfish poisoning. The latter is a taxon that sporadically occurs in the tropical Mexican Pacific. This study describes the behavior of both taxa throughout the annual cycle and analyzes their morphology, abundance, distribution, and their bloom dynamics, in relation to environmental and climatological parameters. Methods: Phytoplankton collections were made ten times from October 2009 to January 2011 within Acapulco Bay and its surroundings, together with measurements of physicochemical parameters. Climatic data were obtained from Acapulco weather station. Abundance of phytoplankton was evaluated with the Utermohl method. Statistical analyses were carried out to investigate the relationship of Gc and Pbc abundances with environmental and climatic parameters. Key results: Gc was present throughout the year 2010 in low densities and in November 2010 it reached a maximum of 189×103 cells l-1, associated with several species of diatoms and dinoflagellates, including Pbc. Gc bloom coincided with decrease in ammonium and decrease in water temperature with respect to the average. Pyrodinium bahamense morphometry from Acapulco corresponds to var. compressum. Pbc formed an intense HAB in July 2010 (reaching a maximum abundance of 773×103 cells l-1), causing significant toxicity and had an upturn in November. Conclusions: Pbc HABs in Acapulco require the occurrence of a previous HAB in the central Pacific or Gulf of Tehuantepec, Mexico, horizontal transportation of their cysts, as well as high water temperature conditions, abundant rainfall that increased the concentration of phosphates, which is propitiated in the periods of transition El Ninoˮ-La Ninaˮ events. Gc HABs in Acapulco are related to “La Nina” events, with an abrupt change in water temperature and an increase in nitrogenous forms. Key words: ENSO, Gymnodinium catentum, HAB, Mexican tropical Pacific, morphometry, Pyrodinium bahamense var. compressum. Resumen: Antecedentes y Objetivos: Los florecimientos algales nocivos (FAN) ocurren comunmente en el Pacifico mexicano, siendo importantes los de Gymnodinium catenatum (Gc) y Pyrodinium bahamense var. compressum (Pbc), dinoflagelados productores de saxitoxina que causan envenenamiento paralitico por mariscos. Pbc se presenta esporadicamente en el Pacifico tropical mexicano. El estudio describe el comportamiento de ambos taxa en un ciclo anual y analiza su morfologia, abundancia, distribucion y dinamica del FAN en relacion con parametros ambientales y climatologicos. Metodos: Se realizaron diez recolectas de fitoplancton (octubre 2009-enero 2011) en la Bahia de Acapulco y zona costera adyacente, y mediciones de parametros fisicoquimicos. Los datos climaticos se obtuvieron de la estacion meteorologica de Acapulco. La abundancia del fitoplancton se evaluo con el metodo de Utermohl. Se realizaron analisis estadisticos para investigar la relacion de las abundancias de Gc y Pbc con parametros ambientales y climaticos. Resultados clave: Gc estuvo presente durante todo el ano 2010 con densidades bajas; en noviembre de 2010 alcanzo un maximo de 189×103 celulas l-1, asociado con especies de diatomeas y dinoflagelados, incluyendo Pbc. El florecimiento de Gc coincidio con disminucion de amonio y disminucion de temperatura del agua con respecto al promedio. La morfometria de Pb de Acapulco correspondio con la var. compressum. Pbc formo un intenso FAN en julio de 2010 (abundancia maxima de 773×103 celulas l-1), causando una toxicidad significativa y tuvo un repunte en noviembre. Conclusiones: Los FAN de Pbc en Acapulco requieren un FAN previo en el Pacifico central o en el Golfo de Tehuantepec, transporte horizontal de sus quistes, alta temperatura del agua y abundante precipitacion que aumente la concentracion de fosfatos; condiciones que se propician en los periodos de transicion”El Nino”-La Nina”. Los FAN de Gc en Acapulco estan relacionados con eventos “La Nina”, siendo importantes el cambio abrupto de temperatura del agua y el aumento de formas nitrogenadas. Palabras clave: ENSO, FAN, Gymnodinium catentum, morfometria, Pacifico tropical mexicano, Pyrodinium bahamense var. compressum.