engleski

Picoplankton composition related to mesoscale circulation on the Albanian boundary zone (Southern Adriatic) in late spring

The research cruise was carried out in May 2009 on a 75 km long transect in a SW direction from the Drini Bay shelf, across its edge and along the continental slope. To characterise picoplankton distribution in the boundary zone of the southern Adriatic we combined epifluorescence microscopy, flow cytometry and high-performance liquid chromatography data with hydrographic observations. Picoplankton distribution was greatly influenced by the hydrographic conditions prevailing in the southern Adriatic because of the influence of the Levantine Intermediate Water (LIW) and Eastern Adriatic Current (EAC) forcing. Heterotrophic bacteria numerically dominated the picoplankton community through the entire transect with no significant accumulation. By contrast, picophytoplankton accumulated in the 50–75 m layer, forming a pronounced deep chlorophyll maximum. Synechococcus dominated the photosynthetic picoplankton, whereas picoeukaryotes were numerically the least abundant. The intrusion of warm LIW, which is characteristic of the EAC May maximum, was observed in the layer between 100 and 350 m. LIW intrusion was followed by Prochlorococcus and Synechococcus peaks (10 × 103 cell mL–1 and 90 × 103 cell mL-1, respectively), as well as by the appearance of two Synechococcus ecotypes. The largest number of picoeukaryotes was observed at the offshore stations, where geostrophic current calculation revealed the strongest EAC influence. A strong EAC spread over the central and eastern basin acted like a barrier for Prochlorococcus growth, whereas the picoeukaryote maxima coincided with the core of the EAC, suggesting its persistence to mesoscale instabilities.

picophytoplankton; Levantine Intermediate Water; southern Adriatic

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