Preprints
https://doi.org/10.5194/os-2021-124
https://doi.org/10.5194/os-2021-124

  06 Jan 2022

06 Jan 2022

Review status: this preprint is currently under review for the journal OS.

Influence of cyclonic and anti-cyclonic eddies on plankton biomass, activity and diversity in the southeastern Mediterranean Sea

Natalia Belkin1, Tamar Guy-Haim1, Maxim Rubin-Blum1, Ayah Lazar1, Guy Sisma-Ventura1, Rainer Kiko2, Arseniy R. Morov1, Tal Ozer1, Isaac Gertman1, Barak Herut1, and Eyal Rahav1 Natalia Belkin et al.
  • 1Israel Oceanographic and Limnological Research, Haifa, Israel
  • 2Sorbonne Université, Laboratoire d'Océanographie de Villefranche, Villefranche-sur-Mer, France

Abstract. Planktonic food-webs were studied contemporaneously in a mesoscale cyclonic (upwelling, ~13 months old) and an anti-cyclonic (down-welling, ~2 months old) eddies, as well as in an uninfluenced-background situation in the oligotrophic southeastern Mediterranean Sea (SEMS) during late summer 2018. We show that integrated nutrients concentrations were higher at the cyclone compared to the anti-cyclone or the background stations by 2–13 fold. Concurrently, Synechococcus and Prochlorococcus were the dominant community component abundance-wise in the oligotrophic anti-cyclone (~300 × 1010 cells m−2). In the cyclone, pico- and nanoeukaryotes such as dinoflagellates, Prymnesiophyceae and Ochrophyta contributed substantially to the total phytoplankton abundnce (~14 × 1010 cells m−2) which was ~65 % lower in the anti-cyclone/background stations (~5 × 1010 cells m−2). Primary production was highest in the cyclonic eddy (191 mg C m−2 d−1) and was 2–5 fold lower outside the eddy area. The calculated doubling time of phytoplankton was ~3 days in the cyclone and ~5–10 days at the anti-cyclone/background stations, further reflecting the nutritional differences between these environments. Heterotrophic prokaryotic cell-specific activity was highest in the cyclone (~10 fg C cell−1 d−1), while the least productive cells were found in the anti-cyclone (4 fg C cell−1 d−1). The calculated doubling time of heterotrophic bacteria were 1.4 days in the cyclone and 2.5–3.5 days at the anti-cyclone/background stations. Total zooplankton biomass in the upper 300 m was tenfold higher in the cyclone compared with the anti-cyclone or background stations (1337 vs. 112–133 mg C m−2, respectively). Copepod diversity was much higher in the cyclone (44 species), compared to the anti-cyclone (6 small-size species). Our results highlight that cyclonic and anti-cyclonic eddies show significantly different community compositions and food-web dynamics in oligotrophic environments, with cyclones representing productive oases in the marine desert of the SEMS.

Natalia Belkin et al.

Status: open (until 03 Mar 2022)

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Natalia Belkin et al.

Natalia Belkin et al.

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Short summary
We studied how distinct water circulations that elevate (cyclone) or descend (anti-cyclone) water from the upper ocean affect the biomass, activity and diversity of planktonic microorganisms in the impoverished eastern Mediterranean. We show that cyclonic and anti-cyclonic eddies differ in their community composition and production. Moreover, the anti-cyclone may be a potential bio-invasion and dispersal vector, while the cyclone may serve as a thermal refugee for native species.