engleski

Phytoplankton pigment signatures in the Gulf of Trieste related to major freshwater inputs during 1992

Background and purpose: Photosynthetic pigments are useful biomarkers of the abundance, composition and physiological status of the phytoplankton biomass in the marine environment. The scope of our study was to investigate phytoplankton dynamics as reflected by seasonal variability of pigment biomarkers in a temperate region characterised by significant and seasonally variable freshwater inputs. Materials and methods: Chlorophyll and carotenoid pigments as well as breakdown products of chlorophyll a were determined using reversed-phase high-performance liquid chromatography (RP HPLC) equipped with serially coupled spectrophotometric and spectrofluorimetric detectors. Results: Chlorophyll a concentrations varied mostly between 100 and 2000 ng/l with maxima clearly related to major freshwater inputs. The most prominent accessory pigments were fucoxanthin, 19'-hexanoyloxyfucoxanthin and chlorophyll b, varying in ranges 20-1200 ng/l, 5-360 ng/l and 1-780 ng/l, respectively. This indicated diatoms, prymnesiophytes and green algae as the most abundant phytoplankton groups. The other minor taxonomic marker pigments included 19'-butanoyloxyfucoxanthin, peridinin and zeaxanthin/lutein. The major nutrient input by rivers and rain in March/April was followed by a large increase of diatoms (fucoxanthin). Depletion of orthosilicate and nitrate in late spring caused a decline of the diatom bloom and resulted in a shift in dominant phytoplankton from diatoms to small flagellates. This was reflected by a significant decrease in the fucoxanthin/19'-hexanoyloxyfucoxanthin ratio from 5-29 to 0.2-1. Prymnesiophytes and diatoms dominated the phytoplankton throughout the whole summer, while intense rain events during the autumn overturn induced a concomitant increase of diatoms (fucoxanthin) and green algae (chlorophyll b). Conclusion: Photosynthetic pigment composition reflected clearly the impact of major freshets on the seasonal dynamics of phytoplankton in the Gulf of Trieste. Compared with the conventional light-microscopy chemotaxonomic approach provided a more detailed insight into the composition of nanoplankton and indicated prymnesiophytes and green algae as the major constituents of phytoplankton biomass.

phytoplankton; photosynthetic pigments; freswater inputs; northern Adriatic

nije evidentirano