MS Defense Seminar of Prisca Lim

Drivers of marine phytoplankton diversity and connectivity in the Galápagos Archipelago spanning an ENSO cycle

The Galápagos Islands lie on the intersection of multiple converging ocean currents, bringing unique environmental conditions to the archipelago which supports relatively high biodiversity and productivity in the region. The Equatorial Undercurrent (EUC) provides cold, nutrient-rich waters into the sunlit surface waters surrounding the Galápagos Islands, supporting diverse communities of marine protists and lowering ocean temperatures, particularly on the Western side of the archipelago. Autotrophic bacteria and protists (i.e., phytoplankton), play a critical role at the base of the Galápagos marine food chain. Hence, elucidating the drivers of marine phytoplankton dynamics is crucial in guiding conservation efforts in the region. A series of research cruises were conducted in the Fall between 2014 and 2022 around the Galápagos Islands, including an El Niño event in 2015 and a La Niña event in 2022. Oceanographic measurements from these cruises indicate variations in physical and chemical properties along with high heterogeneity in protist composition throughout the archipelago. Stations characterized by EUC influence were mostly composed of larger (>5 µm) phytoplankton whereas at warmer, low nutrient sites, small (<5 µm) phytoplankton dominate biomass and productivity. Correlation analysis identified distinct plankton communities associated with specific environmental conditions that occurred both spatially and temporally. These findings shed light on how different factors affect phytoplankton dynamics and resulting primary productivity within the unique and diverse ecosystem of the Galápagos Islands.