2 research outputs found
Structure and photosyntetic properties of phytoplankton assemblages in a highly dynamic system, the Northern Adriatic Sea
The photosynthetic properties of phytoplankton populations as related to physicalechemical variations on small temporal and spatial scales
and to phytoplankton size structure and pigment spectra were investigated in the Northern Adriatic Sea off the Po River delta in late winter 1997.
Large diatoms (fucoxanthin) dominated the phytoplankton in the coastal area whereas small phytoflagellates (mainly 190-hexanoyloxyfucoxanthin,
chlorophyll b, 190-butanoyloxyfucoxanthin) occurred outside the front. The front was defined by the steep gradient in density in the surface
layer separating low-salinity coastal waters from the offshore waters.
Physical features of the area strongly influenced phytoplankton biomass distributions, composition and size structure. After high volumes of
Po River discharge several gyres and meanders occurred in the area off the river delta in February. Decreasing river discharge and the subsequent
disappearance of the gyres and the spreading dilution of the river plume was observed in March. The dynamic circulation of February resulted in
high photosynthetic capacity of the abundant phytoplankton population (>3.40 mg m3). In March, the slow circulation and an upper lowsalinity
water layer, segregated from the deeper layers, resulted in lack of renewal of this water mass. The huge phytoplankton biomass, up
to 15.77 mg chl a m3, became nutrient depleted and showed low photosynthetic capacity. In February, an exceptionally high Pmax
B ,
20.11 mg C (mg chl a)1 h1 was recorded in the Po River plume area and average Pmax
B was three-fold in February as compared to the March
recordings, 10.50 mg C (mg chl a)1 h1 and 3.22 mg C (mg chl a)1 h1, respectively.
The extreme variability and values of phytoplankton biomass in the innermost plume area was not always reflected in primary production.
Modeling of circulation patterns and water mass resilience in the area will help to predict phytoplankton response and biomass distributions. In
the frontal area, despite a considerable variability in environmental conditions, our findings have shown that the phytoplankton assemblages will
compensate for nutrient depression and hydrographic constraints, by means of size and taxonomic composition and, as a result, the variability in
the photosynthetic capacity was much less pronounced than that observed for other parameters