Trophic dynamics between phytoplankton and microzooplankton in the Ria Formosa coastal lagoon system

• Autor(a) principal: Sá, Bárbara Andreia dos Santos de Sousa e
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Texto Completo: http://hdl.handle.net/10400.1/10039
• topic: Fitoplâncton; Microzooplâncton; Mortalidade; Predação; Método de diluição; Ria Formosa

Phytoplankton is a planktonic group with great importance to the aquatic ecosystems, because constitutes the base of the food web, and have an important play role in the oxygen production and carbon dioxide consumption. Grazing by phagotrophic protists (microzooplankton) is considered the major mortality source of phytoplankton in the oceans. Thus, understanding the trophic dynamics between these two planktonic groups is essential for a better understanding of the functioning and variability of aquatic ecosystems. Trophic dynamics between phytoplankton and microzooplankton in the Ria Formosa coastal lagoon system (south Portugal) was studied through a seasonal sampling, with a period of one year. The methodology used in the experiments was the dilution technique, with and without enrichment of inorganic macronutrients, in two distinct places of Ria Formosa (inner station of the lagoon system and an outer station which is in contact with the adjacent coastal region) and in different periods of time (spring and autumn). The analyses of phytoplankton biomass were done through fluorimetry, while the phytoplankton and microzooplankton composition and abundance were through epifluorescence microscopy (< 20 μm) and inverted microscopy (> 20 μm). The temperature and salinity values were under the Ria Formosa normal standers. Chl a had high seasonal variations, such that values obtained during the spring of 2015 followed the Chl a standards for the Ria Formosa, while values for the spring of 2016 did not. Cyanobacteria dominated the phytoplankton community in both seasons. It were performed six sets of experiments, and four of them had unexpected responses regarding the relationship between dilution factors and the apparent growth rate of phytoplankton. It was obtained non-significant linear regressions and positive linear regressions, showing that sometimes the dilution has a negative effect on phytoplankton. Microzooplankton removed, daily, between 44.83% and more than 100% of phytoplankton production. The growth rate of phytoplankton was between 0.05 d-1 and 2.22 d-1.