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- Phytoplankton communities in two wide-open bays in the Iberian upwelling systemPublication . Santos, Mariana; Moita, Maria Teresa; Oliveira, Paulo B.; Amorim, AnaThe main meteorological and oceanographic drivers shaping phytoplankton community structure and dynamics are investigated in two wide-open bays influenced by coastal upwelling. Local processes influencing the proliferation of harmful algal bloom species were also investigated. The work was developed during one year in Lisbon Bay (central-west coast) and in Lagos Bay (south coast), both located on the upwelling shadow of prominent headlands. In both bays, the results indicated a bi-modal annual pattern in phytoplankton biomass, and phytoplankton concentration maxima, between spring and late-summer, were associated with high diatom abundances. In Lagos Bay, higher dinoflagellate abundances were observed from spring to autumn, while in Lisbon Bay these were recorded from late-summer to autumn. The coccolithophores were a frequent group all year round in Lisbon Bay, which contrasts with Lagos Bay where they were the least frequent group. The phytoplankton community structure showed significant spatial and seasonal differences. The community succession pattern indicated the existence of four biological seasons in Lisbon Bay and at the offshore site in Lagos Bay. By contrast, the nearshore site in Lagos Bay was characterized by having no significant differences between summer and autumn. Differences in HAB species/groups were also observed between the bays. In general, HABs occurred at higher concentrations and were more persistent in Lagos Bay. In both bays, winter assemblages were influenced by water column mixing processes, although precipitation was also relevant in Lagos. Upwelling was a key driver of the spring phytoplankton community in Lagos Bay, while in Lisbon Bay other factors seemed to drive the spring phytoplankton assemblages. Both summer and autumn communities were related to thermal stratification. In autumn, the occurrence of reversal circulation patterns also played an important role in shaping the phytoplankton communities, especially in Lagos Bay. Overall, this study revealed differences on phytoplankton community patterns in two wide-open bays, shaped by the local environmental variables.
- Characterizing phytoplankton biomass seasonal cycles in two NE Atlantic coastal baysPublication . Santos, Mariana; Mouriño, Helena; Calixto De Jesus Moita Garnel, Maria Teresa; Silva, Alexandra; Amorim, Ana; Oliveira, Paulo B.The seasonal and interannual variability of chlorophyll a was studied between 2008 and 2016 in two coastal bays located in the northeastern limit of the Iberia/Canary upwelling ecosystem. The work aims (i) to understand if small latitudinal distances and/or coastline orientation can promote different chlorophyll a seasonal cycles; and (ii) to investigate if different meteorological and oceanographic variables can explain the differences observed on seasonal cycles. Results indicate three main biological seasons with different patterns in the two studied bays. A uni-modal pattern with a short early summer maximum and relatively low chlorophyll a concentration characterized the westernmost sector of the South coast, while a uni-modal pattern characterized by high biomass over a long period, slightly higher in spring than in summer, and high chlorophyll a concentration characterized the central West coast. Comparisons made between satellite estimates of chlorophyll a and in situ data in one of the bays revealed some important differences, namely the overestimation of concentrations and the anticipation of the beginning and end time of the productive period by satellite. Cross-correlation analyses were performed for phytoplankton biomass and different meteorological and oceanographic variables (SST, PAR, UI, MLD and precipitation) using different time lags to identify the drivers that promote the growth and the high levels of phytoplankton biomass. PAR contributed to the increase of phytoplankton biomass observed during winter/midspring, while upwelling and SST were the main explanatory drivers to the high Chl-a concentrations observed in late-spring/summer. Zonal transport was the variable that contributed most to the phytoplankton biomass during late-spring/summer in Lisbon Bay, while the meridional transport combined with SST was more important in Lagos Bay.