Application of chemotaxonomy to the study of the phytoplankton community structure in the Mediterranean Sea and in the Atlantic and Southern Oceans = Aplicación de la quimiotaxonomía al estudio de la estructura de la comunidad fitoplanctónica en el Mar Mediterráneo y en los oceános Atlántico y Antártico

Abstract

Despite their small size, phytoplankton represents up to 50% of the global primary production of the Earth and serves as a connector between oceanic and atmospheric processes. Therefore, phytoplankton constitutes a central pillar in the comprehension of the cycles of mass and energy in the oceans. Their different attributes like size, abundance, community composition, functions, pigment complex and taxonomy provide relevant information to understand the processes of global change. In the past decades, the use of HPLC chromatography (High-Performance Liquid Chromatography) has proven as a very effective methodology to study marine phytoplankton. This technique, combined with the use of the statistic program CHEMTAX, allows to identify efficiently the contribution of certain taxonomic classes. This thesis is centered around the use of HPLC-CHEMTAX to identify the phytoplanktonic communities of three regions: the Mediterranean Sea, the Atlantic Ocean and the Antarctic Ocean, each characterized by different trophic conditions (from oligotrophic to eutrophic). With the results obtained, we expect to contribute to the comprehension of the local biochemical responses in a context of global change, as well as to improve future models of ecosystems and algorithms for remote sensing. To validate the data obtained, the results originated from the HPLC-CHEMOTAX were compared to other techniques used for identification and quantification, such as microscopy, flow cytometry and bio-optics. First, we focused on a temporal series (14 years) where we analyzed the seasonal and inter-annual dynamics of the phytoplanktonic community. We have verified that the phytoplanktonic community follows a seasonal pattern, just as had been observed in previous studies: diatoms dominated the blooms of late winter/early spring, while Synechococcus showed maximum abundances during the months of April and August. The cryptophytes and dinoflagellates showed a positive response to sporadic fertilization events, associated mainly to stormy events. In the next study of this thesis, we analyzed the size fractions obtained from sequential filtrations by HPLC-CHEMTAX (total, n+m>3 µm and pico<3 µm) and we compared the results obtained with the algorithms proposed by Vidussi et al. (2001), Uitz et al. (2006) and Hirata et al. (2011). We also measured the specific absorption coefficient of phytoplankton and we compared it with size indicators. Our observations suggest that studies using size fractionation can inform about the sturcture of sizes of a community and that the absorption coefficient of phytoplankton is mainly associated with the pigment composition of the cells and the photoacclimation processes in different phytoplanktonic communities. Finally, with the aim of describing the diversity, abundance and physiologic characteristics of the phytoplanktonic community associated with the formation of marine aerosols, we have used the HPLC-CHEMOTAX in the Antarctic Ocean. Our study highlighted the association of cryptophytes in stratified surface waters influenced by ice fusion, the bloom of diatoms in South Georgia, an area rich in iron, as well as the substantial contributions of less studied groups such as the pelagophytes. In summary, this thesis shows the effectiveness of the HPLC-CHEMOTAX to study phytoplanktonic communities in varying ecological processes and environmental conditions. And in addition, the results obtained demonstrate that the HPLC-CHEMOTAX is also appropriate to quantify simultaneously different size classes of phytoplankton.

El fitoplancton constituye un pilar central necesario para la comprensión de los ciclos de materia y energía de los océanos. Sus atributos como el tamaño, abundancia, comunidades, etc., proporcionan información relevante para entender los procesos de cambio global. En las últimas décadas, el uso de la cromatografía por HPLC se ha revelado como una metodología efectiva para el estudio del fitoplancton marino. Dicha técnica combinada con la utilización del programa estadístico CHEMTAX permite identificar de forma eficiente la contribución de diversas clases taxonómicas. Esta tesis se ha centrado en el uso del HPLC-CHEMTAX para identificar las comunidades fitoplanctónicas en tres regiones: el Mar Mediterráneo, el Océano Atlántico y el Océano Antártico. Con los resultados obtenidos esperamos contribuir a la comprensión de las respuestas biogeoquímicas locales en un contexto de cambios globales, así como mejorar futuros modelos de ecosistemas y algoritmos para sensores remotos. Para validar los datos obtenidos, los resultados provenientes del HPLC-CHEMTAX fueron comparados con otras técnicas de identificación y cuantificación, tales como microscopía, citometría de flujo y bio-óptica. Primeramente, nos centramos en una serie temporal (14 años) donde se analizaron las dinámicas estacionales e interanuales de las comunidades fitoplanctónicas. En el siguiente estudio hemos analizados las fracciones de tamaño obtenidas por filtraciones seriadas con HPLC-CHEMTAX (total, n+m>3 µm y pico<3 µm) y comparamos los resultados obtenidos con los algoritmos propuestos por Vidussi et al. (2001), Uitz et al. (2006) e Hirata et al. (2011). Medimos el coeficiente específico de absorción del fitoplancton y se comparó con indicadores de tamaño. Finalmente, con la finalidad de describir la diversidad, abundancia y características fisiológicas de la comunidad fitoplanctónica en relación con la formación de aerosoles marinos, se ha utilizado el HPLC-CHEMTAX en el Océano Antártico Esta tesis prueba la eficacia del uso del HPLC-CHEMTAX para el estudio de las comunidades fitoplanctónicas en distintos procesos ecológicos y condiciones ambientales. Además, los resultados obtenidos demuestran que el HPLC-CHEMTAX es adecuado para cuantificar e identificar simultáneamente distintas clases de tamaño de fitoplancton.