engleski

Phytoplankton community dynamics in the coastal north-eastern Adriatic Sea

Understanding phytoplankton dynamics is essential for grasping how the marine ecosystem functions, and predicting how it may be affected by human activities. This is particularly important in marginal seas such as the Adriatic where the small water body, with at times restricted circulation, can result in amplified responses to external changes. This study considers phytoplankton dynamics in relation to variable environmental conditions. Sampling was carried out twice a month in the period from September 2008 till October 2009 at a coastal station 1 nm in front of Rovinj. Two independent methods for the estimation of phytoplankton community composition were applied and compared: pigment analysis by high performance liquid chromatography (HPLC) and inverted light microscope cell counts. Pigment analysis pointed to a clear domination of haptophytes in the investigated area. High concentrations of 19’-hexanoyloxyfucoxanthin were recorded throughout the year with a distinct peak in the late spring. This late spring period was characterised by a high species diversity of coccolithophorida. Emiliania huxleyi was the most frequently recognised species with highest abundances in the winter and was negatively associated with temperature (R=-0.35, p<0.001). Microscopic analysis revealed diatoms as the most dominant group, with highs in the autumn 2008 and summer 2009. Both events coincided with the spread of Po River over the stable water column, indicated by wider ranges of temperature, density anomaly and salinity, and confirmed by positive associations of diatoms with temperature (R=0.29, p<0.001) and negative with salinity (R=-0.14, p<0.001). In general, observations made here are in line with previous studies of phytoplankton pigments and community composition in the oligotrophic part of the northern Adriatic Sea.

photosynthetic pigments; haptophytes; diatoms

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