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How phytoplankton physiology and community structure adjust to physical forcing in a coastal ecosystem (northern Adriatic Sea)

March 15, 2014

We investigated how variability in physicochemical properties influenced photosynthetic parameters and the phytoplankton community in the shallow coastal waters of the Adriatic Sea (Gulf of Trieste), where local rivers greatly influenced the dynamics of the system. During the study period (May 2009–July 2010), high sea-surface temperatures in summer, freshwater inputs and precipitation influenced the stability of the water column and the distribution of major nutrients. Redundancy analysis showed a significant effect of total inorganic nitrogen, silicate and salinity on the distribution of the surface phytoplankton community. The modest chlorophyll a (Chl a) concentration exhibited higher variability [coefficient of variation(C.V.) = 60–69%] compared with the photosynthetic parameters. Among them, photosynthetic capacity (PBmax) showed smallest variation (C.V. =37–45%) and no significant vertical or temporal variability was observed. PBmaxsignificantly correlated with temperature, although indirect control by other environmental factors should not be overlooked. During the stratified period, significant vertical differences were observed in photosynthetic efficiency [αB: 0.009 and 0.014 mg C (mg Chl a)−1 h−1 (μmol photon m−2 s−1)−1 at the surface and 15 m, respectively] and in the light saturation index (Ek: 270 and 172 μmol photon m−2 s−1 at the surface and 15 m, respectively), revealing photoacclimation in the communities. Both parameters also tended to be different in the more homogenous water column during winter. Using a ratio between available light and Ek, this study demonstrated light-limited photosynthesis for the greater proportion of the water column, drawing attention to the vertical variability in αB that could, if disregarded, have a significant effect on the assessment of depth-integrated primary production.

Talaber I, Francé J, Mozetic P, 2014: How phytoplankton physiology and community structure adjust to physical forcing in a coastal ecosystem (northern Adriatic Sea),  Phycologia,  53(1), 74-85. Article (subscription required).

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