Diel dynamics of dissolved organic matter and heterotrophic prokaryotes reveal enhanced growth at the ocean's mesopelagic fish layer during daytime
AuthorsMoran, Xose Anxelu G.
García, Francisca C.
Calleja, Maria L.
KAUST DepartmentBiological and Environmental Science and Engineering (BESE) Division
Marine Science Program
Red Sea Research Center (RSRC)
King Abdullah University of Science and Technology (KAUST), Red Sea Research Center, Biological and Environmental Science & Engineering Division, 23955-6900 Thuwal, Saudi Arabia.
Permanent link to this recordhttp://hdl.handle.net/10754/670973
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AbstractContrary to epipelagic waters, where biogeochemical processes closely follow the light and dark periods, little is known about diel cycles in the ocean's mesopelagic realm. Here, we monitored the dynamics of dissolved organic matter (DOM) and planktonic heterotrophic prokaryotes every 2 h for one day at 0 and 550 m (a depth occupied by vertically migrating fishes during light hours) in oligotrophic waters of the central Red Sea. We additionally performed predator-free seawater incubations of samples collected from the same site both at midnight and at noon. Comparable in situ variability in microbial biomass and dissolved organic carbon concentration suggests a diel supply of fresh DOM in both layers. The presence of fishes in the mesopelagic zone during daytime likely promoted a sustained, longer growth of larger prokaryotic cells. The specific growth rates were consistently higher in the noon experiments from both depths (surface: 0.34 vs. 0.18 d-1, mesopelagic: 0.16 vs. 0.09 d-1). Heterotrophic prokaryotes in the mesopelagic layer were also more efficient at converting extant DOM into new biomass. These results suggest that the ocean's twilight zone receives a consistent diurnal supply of labile DOM from diel vertical migrating fishes, enabling an unexpectedly active community of heterotrophic prokaryotes.
CitationMorán, X. A. G., García, F. C., Røstad, A., Silva, L., Al-Otaibi, N., Irigoien, X., & Calleja, M. L. (2021). Diel dynamics of dissolved organic matter and heterotrophic prokaryotes reveal enhanced growth at the ocean’s mesopelagic fish layer during daytime. Science of The Total Environment, 150098. doi:10.1016/j.scitotenv.2021.150098
JournalScience of The Total Environment
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