In this work we focused on the phytoplankton cell size structure in three eutrophic coastal lagoons (Calich, Santa Giusta and Corru S’Ittiri) located in the same geographic region (North Western Mediterranean Sea), but differing in geomorphology, width of catchment area, water temperature, water transparency, salinity and nutrient concentrations. Two cell size classes were considered: picophytoplankton (Pico, 0.2 - 2 µm) and Utermhöl fraction of phytoplankton (UFP, > 2 µm). The objectives of the study were to assess: i) which was the contribution of each cell size class to total phytoplankton abundance and biovolume, ii) how the abundance and biovolume of each cell size class responded to seasonal environmental variations, and iii) which environmental variables, among water temperature, water transparency, salinity, dissolved inorganic nitrogen (DIN) and reactive phosphorus (PO4), affected significantly the seasonal dynamic of the two cell size classes. The major Pico contribution to total phytoplankton was in terms of density, with percentages > 70% in C. S’Ittiri and in S. Giusta (maximum contribution in spring), and > 60% in Calich (maximum contribution in winter). Instead, UTF dominated total phytoplankton biovolume. In this case, maximum Pico contribution was observed in summer in Calich (0.25%) and S. Giusta (0.02%), and in autumn in C. S’Ittiri (0.05%). The environmental drivers that significantly affected Pico and UTF seasonal dynamic resulted case study specific. Higher temperature and salinity favored UTF abundance and Pico abundance and biovolume in Calich and S. Giusta. These conditions disadvantaged, instead, UTF biovolume in both sites. Higher DIN concentrations favored UTF biovolume, disadvantaging Pico biovolume in Calich. On the other hand, higher PO4 values favored Pico biovolume, disadvantaging UTF biovolume in S. Giusta. In C. S’Ittiri, UTF abundance was favored by higher temperature, while UTF biovolume was favored by lower transparency and DIN and PO4 values. In opposite, higher transparency and higher DIN and PO4 concentrations favored Pico abundance and biovolume.
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|Titolo:||Seasonal variations of phytoplankton size classes in relation to environmental variables in three Mediterranean coastal lagoons|
|Data di pubblicazione:||2017|
|Appare nelle tipologie:||4.2 Abstract in Atti di convegno|