Combined effects of turbulence and nutrient enrichment on competition dynamics between diatoms and heterotrophic bacteria

• Autor(a) principal: Mosley, Benjamin Andrew
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/16682
• topic: Diatoms; Heterotrophic bacteria; Phytoplankton; Competition; Turbulence; Microbial food-web; Domínio/Área Científica::Ciências Naturais::Outras Ciências Naturais

Time series data of Chlorophyll a, dissolved organic carbon, heterotrophic bacteria and autotrophic biomass obtained from incubations of water samples collected 1 km south from El Masnou, (Mediterranean Sea) were analysed. This was used to explore the competitive dynamics of heterotrophic bacteria and diatoms under different environmental conditions and to investigate the influence of turbulence. Eight microcosm experiments were set up with daily addition of nitrogen and phosphorus at Redfield ratios. Groups of containers were enriched or depleted in silicate and glucose. Four of the microcosms were subject to artificial turbulence. The microcosm set-ups were glucose; glucose and silicate; glucose, silicate and turbulence; glucose and turbulence; turbulence only; silicate only; silicate and turbulence; and a control with no addition of silicate or glucose and no turbulence. It was found that turbulence had no influence on the competition between heterotrophic bacteria and diatoms however there was a difference based on the varying silicate or glucose environments. As was to be expected, the bacterial biomass increased rapidly in the microcosms with added glucose. Following this was an increase in autotrophic biomass, particularly when silicate was present, and a subsequent decrease in bacterial biomass, indicating a high level of grazing. In the absence of glucose, the bacteria did not grow as rapidly in the microcosm containing silicate, and there was little change in biomass in the container without silicate. The autotroph numbers increased in the silicate replete microcosm before declining. In the set-up without glucose or silicate, the biomass dropped initially which was expected but then increased. This increase was attributed to bacterial remineralisation of dissolved organic carbon sources, presumably derived from protozoans, flagellates and ciliates. This subsequent remineralisation may have had an impact on diatom growth and reproduction. Turbulence had no significant effect on phytoplankton competition which may highlight a limitation to microcosm experiments.