Microbial plankton community in a semi-enclosed bay affected by upwelling: seasonal evolution and the role of the nutrient trap

1st Meeting of the Iberian Ecological Society & XIV AEET Meeting "Ecology: an integrative science in the Anthropocene", Barcelona, Spain, 4th – 7th February 2019The Ría de Vigo is a semi-enclosed bay on the NW Iberia that is affected by seasonal upwelling (spring to autumn) and where fisheries and aquaculture coexists with other human activities such as ship building and tourism. The microbial plankton community in this system was studied with a sampling frequency of twice a week during a year with the aim of knowing how this community structures and reacts to environmental variability. Autotrophic biomass (AB) dominated from spring to autumn when upwelling prevailed, while AB and heterotrophic biomass (HB) covaried over the year according to HB:AB = 0.26 ± 0.04 (r2 = 0.7) pointing to the link of the two communities. Diatoms and autotrophic nanoflagellates accounted for 80 ± 18% of the AB, whereas the HB was mainly composed of heterotrophic bacteria (36 ± 11%) and heterotrophic nanoflagellates (30 ± 12%). AB and HB, as well as their main components, showed a continuous increase during the upwelling season that was attributed to growth. However, a sudden increase occurred in autumn when downwelling caused the accumulation of biomass before leading to the low values of winter. As upwelling promotes the export of material to the open ocean, the increase in biomass was possible by the existence of a nutrient trap that fuels phytoplankton growth through recycling at the sediment-water interface a substantial part of organic matter previously synthetized in the water column. The reorganization of the community that follows the winter depletion began with the proliferation of small plankton formsPeer reviewe