@phdthesis{8734017,
  abstract     = {{The open ocean accounts for nearly 70% of Earth’s surface and represents the largest habitat in the biosphere. Phytoplankton, which are drifting microorganisms with the capacity to perform oxygenic photosynthesis, support life in this vast environment. Besides, they are a key component of marine ecosystems as they drive the oceanic biological pump, influence biogeochemical cycles and modulate fishing yields. However, climate change modifies the environmental drivers governing phytoplankton photosynthesis and consequently alters their productivity, diversity and community structure. Understanding the phytoplankton response to environmental stressors is mandatory to ascertain the implications of current and future climate changes on marine ecosystems in general.
Important tools in this respect are remote sensing satellite observations and mathematical models. The former provide high-resolution spatial-temporal observations of key ocean variables, while the latter allow to extrapolate knowledge from the laboratory and sparse field observations to global and regional scales. Hence, the main focus of this thesis is the assessment of the marine phytoplankton response to environmental stressors associated with climate change on the basis of multi-platform datasets, i.e. satellite observations and outputs of mathematical models. More specifically, the response of dominant phytoplanktonic cyanobacteria genera on Earth (Prochlorococcus and Synechococcus) to ultraviolet (UV) radiation is investigated as well as the perturbations induced by hurricanes (strongest tropical cyclones (TCs)) on phytoplankton assemblages in several areas of the western North Atlantic Basin in the period 1998–2019.
On the basis of biological weighting function (BWF)/photosynthesis-irradiance (P-E) models, we found that UV accounts for roughly two-thirds of the potential photosynthetic inhibition of Prochlorococcus and Synechococcus in the oceanic photoactive layer in the latitudinal band 40º N/S. Prochlorococcus showed a higher inhibition and integrated photosynthetic potential throughout the water column than Synechococcus, since the former is more vulnerable to UV damage at the surface and more successful at greater depths compared to the latter. On the other hand, we demonstrated that hurricanes trigger vertical and horizontal transport of phytoplankton and nutrients leading to an increased satellite chlorophyll (Chl) a concentration (a proxy for phytoplankton biomass) in the waters surrounding Cuba, the eastern Gulf of Mexico and the western Sargasso Sea. Besides, we illustrated that hurricanes drive connectivity of phytoplankton assemblages between coastal and oceanic environments. Climatological analyses showed that the strongest TC-induced Chl a increases in the western Sargasso Sea have been mainly associated with consecutive TCs as they superimpose effects on the upper-ocean response.
Finally, data of phytoplankton functional types (PFTs) derived from a biogeochemical ocean general circulation model revealed that Prochlorococcus and Synechococcus respond modestly to post-storm nutrient enrichment in the tropical Sargasso Sea as compared to coccolithophores, diatoms, diazotrophs, mixotrophic dinoflagellates, and picoeukaryotes, whose concentrations increase significantly after a hurricane passage. Besides, a significant post-storm increase of the Shannon diversity index values was also observed indicating that a moderate post-storm nutrient increase in this oligotrophic area positively impacts phytoplankton diversity limiting exacerbated productivity of opportunistic species. Overall, this thesis provides a baseline against which future phytoplankton responses to environmental stressors can be evaluated. Its findings fit the needs of future studies on climate change, ecological variability, environmental protection and fisheries oceanography.}},
  author       = {{Avila Alonso, Dailé}},
  isbn         = {{9789463574686}},
  keywords     = {{Phytoplakton,hurricanes,tropical cyclones,ultraviolet radiation,climate change}},
  language     = {{eng}},
  pages        = {{XVIII, 322}},
  publisher    = {{Ghent University. Faculty of Bioscience Engineering}},
  school       = {{Ghent University}},
  title        = {{Marine phytoplankton response to environmental stressors associated with climate change}},
  year         = {{2022}},
}