Picoplankton Diel Variability and Estimated Growth Rates in Epipelagic and Mesopelagic Waters of the Central Red Sea

The diel variability of the abundance and cell size picoplanktonic groups in central Red Sea was monitored every 2 h situ on 4 occasions (once per season) from 2015 to 2016. We distinguished Prochlorococcus , low (LF-Syn) high (HF-Syn) fluorescence Synechococcus small (Speuk) large (Lpeuk) picoeukaryotes two heterotrophic prokaryotes (LNA) (HNA) nucleic acid content. less marked than more apparent autotrophs heterotrophs. Specific growth rates were estimated by an empirical relationship measurements obtained bottle incubations surface deep samples collected winter compared with variations over 24 h. Autotrophic picoplankton generally grew faster (0.23–0.77 d –1 ) (0.12–0.50 ). Surface 100 m depth-weighted specific displayed a clear seasonal pattern for maxima (0.77 ± 0.07 minima fall (0.52 peaked spring, slightly higher LF-Syn (0.57 0.04 HF-Syn (0.43 Speuk Lpeuk showed different patterns, lower values former (0.27 0.02 0.37 respectively). HNA consistently outgrew LNA prokaryotes, epipelagic (0–200 m, 0.36 0.03 mesopelagic (200–700 0.26 ), while no differences found cells (0.19 0.17 With all data pooled, mean abundances autotrophic upper layers significantly correlated variations. Our high-resolution sampling dataset suggests that changes underlie noticeable seasonality recently described these tropical waters.