Structure and dynamics of microbial communities associated with the invasive seaweed Undaria pinnatifida in the Patagonian coast

FERMANI, P.; ZABALA, S. ; GEREA, M.; SEGADE, M.E.; GARCIA, P. E.; UNREIN, F.; DIÉGUEZ, M.C.; LOZADA, M.

Buenos Aires

Congreso; 3er Congreso Latinoamericano de Ecología Microbiana; 2023

Golfo Nuevo, a coastal protected area in a productive and biodiverse marine region of Patagonia (Argentina), is experiencing ecological and economic impacts due to the invasion of the brown alga Undaria pinnatifida. This study evaluates the effect of the exudates and biomass of U. pinnatifida on coastal microbial communities under the premise that changes at this level will affect coastal food webs. Microbial communities associated to surface water and kelp bed water were analyzed in Punta Este (Golfo Nuevo), a site heavily colonized by U. pinnatifida. Flow cytometry showed that the abundance of heterotrophic bacteria (HB), picocyanobacteria (Pcy) and picoeukaryote (Peuk) were related to physico-chemical factors, seasonality and sampling depth, in accordance with bacterial community structure determined by molecular methods. In surface waters, nutrient inputs (NO2-+ NO3-) favored phytoplankton growth increasing Chl-a concentration in winter; while in the algal bed the Chl-a was independent of these nutrients. U. pinnatifida biomass followed a seasonal pattern, peaking in November (301 ± 170 g m-2 dw) and decreasing towards the end of the summer. This decline was coupled with the increase of fresh dissolved organic carbon, higher NH4+concentration and abundance peaks of HB and Pcy. Bacterial communities from the algal bed showed high capability for degrading alginate, a major component of brown algae cell walls. These results show the structure and dynamics of microbial communities are linked to the summer nutrient release from the decaying algal biomass, adding to the effects already known of U. pinnatifida.