Autumn vertical distribution of zooplankton in the oxygen minimum zone of the Eastern Tropical North Pacific

• Published in: Marine environmental research 2023-09, Vol.190, p.106116-106116, Article 106116
• Main Authors: Färber Lorda, Jaime, Data, Bertrand Färber
• Format: Article
• Language: English
• Subjects: Eastern tropical north pacific; Euphausiids; Habitat compression hypothesis; Oxygen minimum zone; Vertical migration; Zooplankton
• ISSN: 0141-1136; 1879-0291
• DOI: 10.1016/j.marenvres.2023.106116

To confirm the Habitat Compression Hypothesis, a cruise to the Eastern Tropical North Pacific (ETNP) took place at the entrance of the Gulf of California, in an area rarely studied at the southern limit of the California Current, where it mixes with waters of the West Mexican Current and the Gulf of California. No significant day-night differences in the vertical distribution (0–500 m depth) of zooplankton were found based on 22 MOCNESS tows and, for the first time, a 48-h cycle of stratified zooplankton sampling. Most zooplankton groups were observed within the upper 100 m, above the oxycline, with oxygen concentrations as low as 45 μmol kg−1. Some California Current-influenced samples showed a slightly different vertical distribution. A ∼50% reduction in the number and abundance of 24 zooplankton groups was recorded within the Oxygen Minimum Zone, from 100 to 500 m depth. Vertical migrator's exceptions include some euphausiid species that migrate into the OMZ during the day. Principal Component Analyses showed that the vertical distribution of zooplankton is limited by oxygen, with a low zooplankton carbon density below ∼100 m depth within the OMZ. The difference between day and night for the upper 0–100 m layer was non-significant (U221 = 57; p = 0.947); however, the data showed great variability. Thus, zooplankton Carbon remains relatively constant, in the upper 100 m, and is available during day and night, in the studied area. •A 48 h cycle of sampling did not show differences between day and night Zooplankton Carbon.•Zooplankton Carbon is the same day and night in the First 100 m layer.•Euphausiids did migrate within the sampled layer (0–500 m).•Most zooplankton groups stayed in the first 100 m in oxygenated waters.•A reduction, with depth, of the 24 main zooplankton groups studied was observed.•Here we verified the so-called Habitat Compression Hypothesis (HCH), for the Entrance of the Gulf of California.