Abstract
The Ria de Vigo is a semienclosed bay in northwestern Iberia that is affected by seasonal upwelling (spring to autumn) that triggers high levels of primary productivity. Fisheries and aquaculture coexist with other human activities, such as shipbuilding and tourism, in this area. The microbial plankton community in this system was studied to understand how this community is structured and progresses seasonally. Autotrophic biomass (AB) dominated from spring to autumn when upwelling prevailed, while AB and heterotrophic biomass (HB) covaried throughout the year as HB:AB = 0.26 ± 0.04 (r2 = 0.7), indicating a link between 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%). The 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 biomass to accumulate before leading to the low values in winter. As upwelling promotes the export of materials to the open ocean, the increase in biomass was possibly due to the existence of a nutrient trap that fueled phytoplankton growth through recycling at the sediment-water interface a substantial portion of the organic matter previously synthetized in the water column. The reorganization of the community that followed the winter decrease in biomass began with the proliferation of small plankton forms.
Highlights
Coastal seas, which represent only 7–10% of the ocean’s surface, account for a large fraction (∼20–30%) of marine primary production (Wollast, 1998; Bauer et al, 2013), which is sustained by high proportions of regenerated nutrients (Billen, 1978; Boynton et al, 2018)
Anthropogenic impacts are still higher in semienclosed bays, where water exchange with the open ocean is limited to some extent
As it is expected that seafood demand and anthropogenic impacts will continue increasing in the future due to population growth, mainly on coastal margins (Hinrichsen, 1994; Sale et al, 2014), knowledge of the functioning of these ecosystems is essential to facilitate their management and ensure the suitable conditions needed to preserve the services that they provide
Summary
Coastal seas, which represent only 7–10% of the ocean’s surface, account for a large fraction (∼20–30%) of marine primary production (Wollast, 1998; Bauer et al, 2013), which is sustained by high proportions of regenerated nutrients (Billen, 1978; Boynton et al, 2018). As it is expected that seafood demand and anthropogenic impacts will continue increasing in the future due to population growth, mainly on coastal margins (Hinrichsen, 1994; Sale et al, 2014), knowledge of the functioning of these ecosystems is essential to facilitate their management and ensure the suitable conditions needed to preserve the services that they provide. In this regard, specific knowledge about the structure and variability in microbial plankton communities is of exceptional relevance. Primary production and the first transfers of matter and energy within the pelagic realm take place in these communities, and microbial plankton bring the supporting services needed for the development of all other ecosystem services (Lubchenco and Petes, 2010)
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