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Picoplankton community structure before, during and after convection event in the offshore waters of the southern Adriatic Sea

Najdek-Dragić, Mirjana; Paliaga, Paolo; Šilović, Tina; Batistić, Mirna; Garić, Rade; Supić, Nastjenjka; Ivančić, Ingrid; Ljubimir, Stijepo; Korlević, Marino; Jasprica, Nenad; Hrustić, Enis; Dupčić Radić, Iris; Blažina, Maria; Orlić, Sandi (2014) Picoplankton community structure before, during and after convection event in the offshore waters of the southern Adriatic Sea. Biogeosciences, 11 . pp. 2645-2659. ISSN 1726-4170

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This paper documents the picoplankton community’s response to changes in oceanographic conditions in the period between October 2011 and September 2012 at two stations belonging to South Adriatic Pit (SAP). The recorded data include the community’s abundance, composition, prokaryotic production rates and bacterial metabolic capacity. The sampling period included an intense sea cooling with formation of exceptionally, record-breaking dense water. We documented an especially intense winter convection episode that completely diluted the core of Levantine intermediate waters (LIW) in a large area encompassing the SAP’s center and its margin. During this convection event the whole picoplankton community had significantly higher abundances with a recorded picoeukaryotic peak at the SAP margin. In the post-convection phase in March prokaryotic heterotrophic production strongly increased in the entire SAP area (up to 50 times ; 456.8 nM C day-1). An autotrophic biomass increase (up to 5 times ; 4.86 µg l-1) and a disruption of a close correspondence between prokaryotic heterotrophic biomass production and cell replication rates were observed only in the center of the SAP, which was not under the influence of LIW. At the SAP’s margin such an effect was attenuated by LIW, since the waters affected by LIW were characterized by decreased concentrations of dissolved inorganic nitrogen, decreased autotrophic biomasses and by increased bacterial biomass production balanced with cell replication rates as well as by the domination of Synechococcus among autotrophic picoplankton. The metabolic capacity was lowest in spring when autotrophic biomass largely increased, while the highest levels found in the pre-convection phase (October 2011) suggest that the system was more oligotrophic before than after the convection event. Furthermore, we showed that metabolic capacity is a trait of bacterial community independent of environmental conditions and tightly linked to cell replication and substrate availability. In contrast, the bacterial community composition appears to be strongly influenced by physico-chemical characteristics of waters (e.g. temperature and nutrients) and environmental forcing (e.g. convection and LIW). Our results showed that the two oceanographic phenomena of the southern Adriatic, strongly relevant for the total production of the Adriatic Sea, winter convection and LIW intrusion, regulate the changes in picoplankton community structure and activities.

Item Type: Article
Uncontrolled Keywords: picoplankton; prokaryotic heterotrophic production; metabolic capacity; South Adriatic Pit
Subjects: NATURAL SCIENCES > Geology
Divisions: Center for Marine Research
Project titleProject leaderProject codeProject type
Struktura i fiziologija mikrobnih zajednica frontalnih zona sjevernog Jadrana-Mirjana Najdek-Dragić098-0982705-2729MZOS
Struktura planktonskih populacija u trofičkom gradijentu u južnom Jadranu-Mirna Batistić275-0000000-3186MZOS
Depositing User: Mirjana Najdek Dragić
Date Deposited: 11 Jul 2016 10:27
DOI: 10.5194/bg-11-2645-2014

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