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

FERMANI, PAULINA; ZABALA SOLEDAD; GEREA MARINA; SEGADE, MARÍA EUGENIA; GARCÍA, PATRICIA E.; UNREIN, FERNANDO; LOZADA MARIANA

MALLORCA

Congreso; ASLO Aquatic Science Meeting; 2023

Golfo Nuevo (Patagonia, Argentina), a coastal protected area located in one of the most productive and biodiverse marine regions, has been invaded by the brown alga Undaria pinnatifida, resulting in significant ecological changes and economic impacts. U. pinnatifida exudates and biomass can be assimilated by microorganisms, with effects on coastal food webs. We analyzed surface and kelp bed-associated picoplanktonic communities in Punta Este, a site in Golfo Nuevo invaded by U. pinnatifida for more than 10 years. 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 analyzed by molecular methods. In surface waters, nutrient inputs (NO2-+ NO3-) favored phytoplankton growth, as reflected by the increase of Chl-a in winter; while no relationship was observed in the algal bed between NO2-+ NO3- and Chl-a. In the algal bed, U. pinnatifida biomass followed a seasonal pattern with maximum values recorded in November (301 ± 170 g m-2 dw) and decreasing towards the end of the summer. This decline was coupled with an increase in dissolved organic carbon, NH4+ and a high abundance of HB and photosynthetic picoplankton cells (Pcy+Peuk). The results show that the structure and dynamics of the microbial communities, in addition to the classic nutrient-based winter enhancement, was also linked to the summer nutrient inputs of the invasive seaweed, adding another effect to those already known for this alga.