Growth and mortality of microbial plankton in the Ria Formosa coastal lagoon

• Autor(a) principal: Santos, Yohann dos
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/20206
• topic: Teia alimentar microbiana; Procariotas heterotróficos; Fitoplâncton; Predação; Lise viral; Método da diluição; Ria Formosa; Domínio/Área Científica::Ciências Naturais::Outras Ciências Naturais

Microbial plankton components interact with each other through fluxes of matter and energy, forming a complex microbial food web. It is well recognized that mortality due to viral lysis and grazing by phagotrophic protists are important processes of biomass removal of heterotrophic prokaryotes and phytoplankton. Since there are only a few studies addressing microbial mortality due to grazing in the Ria Formosa coastal lagoon and the contribution of viruses to prokaryote mortality was never addressed in this ecosystem, the main objective of this study was to evaluate growth and mortality of heterotrophic prokaryotes and phytoplankton in the Ria Formosa coastal lagoon, in order to discuss the quantitative trophic role of microzooplankton and viruses in microbial food web of this important ecosystem. The dilution technique was used to evaluate the impact of microzooplankton on microbial populations of the Ria Formosa coastal lagoon; to estimate the contribution of viruses to heterotrophic prokaryote mortality, modified dilution experiments were also performed. The dilution experiments revealed notable seasonal variations in the growth and grazing rates of heterotrophic prokaryotes and phytoplankton community, with mean grazing rates of 1.66 d-1 and 0.106 d-1 respectively, slightly higher than their mean potential instantaneous growth rate (1.57 d-1 and 0.080 d-1, respectively). These results suggest that microzooplankton consume a significant proportion of heterotrophic prokaryotes and phytoplankton community in the Ria Formosa coastal lagoon. Regarding specific phytoplankton groups, eukaryotic picophytoplankton and cryptophytes showed higher average grazing rates, whereas eukaryotic picophytoplankton showed higher average potential instantaneous growth rates; a wide range of grazing rates among phytoplankton groups is suggestive of selectivity of grazers among taxa and highlights the need to consider and analyze the specific dynamics of each phytoplankton group separately in future studies. On the other hand, this study revealed that viral lysis is a significant source of mortality in late-summer autumn, even exceeding the grazing rates of microzooplankton. Considering the relevance of the Ria Formosa, future studies should focus on these mortality factors, as well as to predict the effects of climate change, and its associated impacts, on these important biomass removal processes.