title: Distribution and diel vertical movements of mesopelagic scattering layers in the Red Sea.
abstract: The mesopelagic zone of the Red Sea represents an extreme environment due to low food concentrations, high temperatures and low oxygen waters. Nevertheless, a 38 kHz echosounder identified at least four distinct scattering layers during the daytime, of which the 2 deepest layers resided entirely within the mesopelagic zone. Two of the acoustic layers were found above a mesopelagic oxygen minimum zone (OMZ), one layer overlapped with the OMZ, and one layer was found below the OMZ. Almost all organisms in the deep layers migrated to the near-surface waters during the night. Backscatter from a 300 kHz lowered Acoustic Doppler Current Profiler indicated a layer of zooplankton within the OMZ. They carried out DVM, yet a portion remained at mesopelagic depths during the night. Our acoustic measurements showed that the bulk of the acoustic backscatter was restricted to waters shallower than 800 m, suggesting that most of the biomass in the Red Sea resides above this depth.
authors.affiliation: King Abdullah University of Science and Technology, Thuwal, 23955-6900 Saudi Arabia.
authors.forename: Thor A
authors.initials: TA
authors.lastname: Klevjer
authors.affiliation: Woods Hole Oceanographic Institution, MS #30, Woods Hole, MA 02543 USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Torres
authors.affiliation: King Abdullah University of Science and Technology, Thuwal, 23955-6900 Saudi Arabia.
authors.forename: Stein
authors.initials: S
authors.lastname: Kaartvedt