Browsing by Author "Mendes, Pedro"
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- Cyanobacteria blooms and cyanotoxin occurrence in the Guadiana (SE - Portugal): preliminary resultsPublication . Caetano, Sandra; Miguel, Rute; Mendes, Pedro; Galvão, Helena M.; Barbosa, Ana B.Cyanobacteria are a recognised public health hazard, because the majority of species is able to produce toxins. The monitoring is usually restricted to freshwater environments, like lakes or dams used for water supply. Cyanobacteria blooms have been regularly reported in the Guadiana River and high estuary and most of the observed cyanobacteria were toxin producers.
- A importância do mundo invisível dos micróbios na Ria FormosaPublication . Mendes, Pedro; Galvão, Helena; Caetano, Sandra; Icely, John; Newton, AliceCom o desenvolvimento da microscopia de epifluorescência e técnicas sensíveis de radioisótopos na década de 1970, a abundância e atividade de microrganismos pôde ser observada e estudada em águas marinhas. Estas observações resultaram num novo conceito de rápida transferência e reciclagem de matéria orgânica através de um ciclo microbiano, o “microbial loop”.
- Role of microbes in the Ria Formosa lagoonPublication . Galvão, Helena M.; Mendes, Pedro; Caetano, Sandra; Icely, John; Newton, AliceWith the development of epifluorescence microscopy and sensitive radioisotope techniques, high abundance and activity of microorganisms was observed in marine waters since 1970s and 1980s. These observations resulted in a new concept of rapid turn-over and recycling of organic matter through a ‘microbial loop’ (Azam et al., 1983; Azam, 1998). Figure 5.1 illustrates fluxes of material through the marine microbial loop. Main processes are C fixation by photosynthetic microorganisms (prokaryotic and eukaryotic) with exudation losses of Dissolved Organic Matter (DOM), which is incorporated by heterotrophic bacteria. Phagotrophic protists in turn graze both autotrophs and bacteria producing ‘sloppy feeding’ loss of DOM, which returns to the loop. DOM is remineralized by all microorganisms into Dissolved Inorganic Nutrients (DIN), which are taken up by autotrophic and heterotrophic microorganisms.
- Short-term variability of heterotrophic bacterioplankton during upwelling off the NW Iberian marginPublication . Barbosa, Ana B.; Galvão, Helena M.; Mendes, Pedro; Álvarez-Salgado, Xose; Figueiras, Francisco; Joint, IanShort-term variability of heterotrophic bacterioplankton was studied in a recently upwelled water mass at the NW Iberian margin (August 1998). Bacterioplankton abundance (BA), biomass (BB), production (BP), and specific production (SBP) were monitored during two Lagrangian drift experiments, one along the shelf-edge, the other off-shelf along an upwelling filament. Other measurements included chlorophyll a (Chla), primary production (PP), suspended particulate organic carbon (POC) and nitrogen (PON), and dissolved organic carbon (DOC) and nitrogen (DON). Although primary production was significantly higher during the shelf-edge drift experiment, bacterial biomass in the euphotic zone (2.68 to 22.20gC.l_1) was not significantly different from that in the offshore filament. In contrast, bacterial production (0.13-3.52gC.l_1.d_1), estimated using an empirically determined 14C-leucine to carbon conversion factor, and bacterial growth rates (doubling time, DT: 3.9–29.7d), were significantly higher during the shelf-edge drift (BP: 1.500.11 versus 0.500.02gC.l_1.d_1; DT: 6.90.3 versus 16.20.9 d; p_0.01). Depth-integrated BB over the euphotic zone comprised 151% of phytoplankton biomass during shelf-edge drift and 394% under the more oligotrophic conditions in the filament. However, daily BP to net primary production ratios were not significantly different in the two regions (61% versus 71%). BA, BB, BP and SBP were enhanced in the later part of the shelf-edge drift following a pronounced increase in both PP and gross DOC production, suggesting that phytoplankton was a source of substrates for bacteria in recently upwelled waters. This contrasted with the filament drift in which short-term variability of bacterioplankton was much less pronounced and there was no correlation between BP and PP. In both regions, SBP and DOC in the euphotic zone were significantly correlated (p_0.005) indicating some regulatory effect of DOC over bacterial activity. Bacterial carbon demand in the euphotic zone ranged from 22.5 to 44.0molC.m_3.h_1, and 10.6 to 11.3molC.m_3.h_1 and represented 62% and 43% of overall gross DOC production during shelf-edge and filament drift experiments. During the filament drift, the relatively high bacterial doubling times coupled with high percentage of non-metabolised DOC (ca. 60%) suggested control of bacteria by either bioavailability of DOM or inorganic nutrients. Between 40 and 60% of gross DOC production was not metabolised by heterotrophic bacteria, thus allowing DOC net accumulation and off-shore advection.