A year in the life of the Eastern Mediterranean: Monthly dynamics of phytoplankton and bacterioplankton in an ultra-oligotrophic sea

Tom Reich, Tal Ben-Ezra, Natalya Belkin, Anat Tsemel, Dikla Aharonovich, Dalit Roth-Rosenberg, Shira Givati, M. Bialik, Barak Herut, Ilana Berman-Frank, Miguel Frada, Michael D. Krom, Yoav Lehahn, Eyal Rahav*, Daniel Sher*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

The Eastern Mediterranean Sea (EMS) is a poorly studied ultra-oligotrophic marine environment, dominated by small-size phyto- and bacterioplankton. Here, we describe the dynamics of a single annual cycle (2018–19) of phyto- and bacterioplankton (abundances, pigments and productivity) in relation to the physical and chemical conditions in the photic water column at an offshore EMS site (Station THEMO-2, ∼1,500 m depth, 50 km offshore). We show that phytoplankton biomass (as chlorophyll a), primary and bacterial productivity differed between the mixed winter (January–April) and the thermally stratified (May–December) periods. Prochlorococcus and Synechococcus numerically dominated the picophytoplankton populations, with each clade revealing different temporal and depth changes indicative to them, while pico-eukaryotes (primarily haptophytes) were less abundant, yet likely contributed significant biomass. Estimated primary productivity (∼32 gC m−2 y−1) was lower compared with other well-studied oligotrophic locations, including the north Atlantic and Pacific (BATS and HOT observatories), the western Mediterranean (DYFAMED observatory) and the Red Sea, and was on-par with the ultra-oligotrophic South Pacific Gyre. In contrast, integrated bacterial production (∼11 gC m−2 y−1) was similar to other oligotrophic locations. Phytoplankton seasonal dynamics were similar to those at BATS and the Red Sea, suggesting an observable effect of winter mixing in this ultra-oligotrophic location. These results highlight the ultra-oligotrophic conditions in the EMS and provide, for the first time in this region, a full-year baseline and context to ocean observatories in the region.

Original languageAmerican English
Article number103720
JournalDeep-Sea Research Part I: Oceanographic Research Papers
Volume182
DOIs
StatePublished - Apr 2022

Bibliographical note

Publisher Copyright:
© 2022 Elsevier Ltd

Keywords

  • Bacterial productivity
  • Eastern mediterranean
  • Levantine basin
  • Phytoplankton
  • Pico-eukaryotes
  • Primary productivity
  • Prochlorococcus
  • Seasonal dynamics
  • Synechococcus

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