Lopez-Sandoval DC, Maranon E, Fernandez A, Gonzalez J, Gasol JM, Lekunberri I, Varela M, Calvo-Diaz A, Anxelu X, Moran G, Alvarez-Salgado XA, Figueira FG
phytoplankton, DOC, Ria de Vigo, mesocosm, upwelling, spring bloom, 3.5 m3, Spain
We studied the importance of dissolved primary production in a coastal, productiveecosystem in relation to phytoplankton biomass, community structure andproductivity. The photosynthetic production of dissolved organic carbon (DOCp)and particulate organic carbon was determined in mesocosm experiments duringfour contrasting oceanographic periods in the R?´a de Vigo (NW IberianPeninsula). We also determined the size-fractionated chlorophyll a concentrationand primary production, phytoplankton taxonomic composition and bacterial production.Phytoplankton biomass was dominated by the .20 mm size fraction(mostly diatoms), except in winter, when the 2–20 and ,2 mm size fractions (flagellatesand picophytoplankton) increased in importance. The percentage of extracellularrelease (PER) had an average value of 19% and was independent ofoceanographic period, phytoplankton biomass and production, taxonomic compositionand size structure. During phytoplankton blooms, PER increased significantlyfrom 14% in the exponential growth phase to 23% in the senescent phase.Bacterial carbon demand and DOCp were uncoupled, suggesting that other processesin addition to photosynthate exudation contribute most of the labile carbonto fuel bacterial metabolism. Dissolved primary production remains an importantprocess in coastal phytoplankton assemblages throughout the year, irrespective ofsize-structure and community composition, but attaining higher significanceduring the decaying phase of blooms.