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Abstract Due to historical under‐sampling of the deep ocean, the distributional ranges of mesopelagic zooplankton are not well documented, leading to uncertainty about the mechanisms that shape midwater zooplankton community composition. Using a combination of DNA metabarcoding (18S‐V4 and mtCOI) and trait‐based analysis, we characterized zooplankton diversity and community composition in the upper 1000 m of the northeast Pacific Ocean. We tested whether the North Pacific Transition Zone is a biogeographic boundary region for mesopelagic zooplankton. We also tested whether zooplankton taxa occupying different vertical habitats and exhibiting different ecological traits differed in the ranges of temperature, Chl‐a, and dissolved oxygen conditions inhabited. The depth of the maximum taxonomic richness deepened with increasing latitude in the North Pacific. Community similarity in the mesopelagic zone also increased in comparison with the epipelagic zone, and no evidence was found for a biogeographic boundary between previously delineated mesopelagic biogeochemical provinces. Epipelagic zooplankton exhibited broader temperature and Chl‐aranges than mesopelagic taxa. Within the epipelagic, taxa with broader temperature and Chl‐aranges also had broader distributional ranges. However, mesopelagic taxa were distributed across wider dissolved oxygen ranges, and within the mesopelagic, only oxygen ranges covaried with distributional ranges. Environmental and distributional ranges also varied among traits, both for epipelagic taxa and mesopelagic taxa. The strongest differences in both environmental and distributional ranges were observed for taxa with or without diel vertical migration behavior. Our results suggest that species traits can influence the differential effects of physical dispersal and environmental selection in shaping biogeographic distributions.
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Projected 21st century compression of mesopelagic habitat in the California current
Abstract Although the mesopelagic zone occupies a substantial volume of the world’s oceans, our results suggest that the livable portion may compress vertically by ~ 40 m or ~ 39% by the end of the century. Using an ensemble of three downscaled climate projections from a high emissions scenario, we evaluated the connection between anthropogenic greenhouse gas emissions and changes in light and oxygen at depth, which influence the upper and lower limits of mesopelagic habitat in the central California Current. Although the model projects a small deepening (~ 2 m) of the upper light boundary consistent with increased stratification and reduced upper ocean productivity, the main driver of vertical mesopelagic habitat compression is the significant shoaling (by ~ 44 m) of the hypoxic boundary over the course of the 21st century. Differences in dissolved oxygen across ensemble members highlight the potential influence of equatorial dynamics and the California Undercurrent in constraining the future availability of mesopelagic habitat along the U.S. west coast. Mesopelagic ecosystems connect the surface ocean to the deep sea, and a projected decrease in the vertical extent of mesopelagic habitat could have cascading effects on a broader range of marine ecosystem processes and carbon export.
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- Award ID(s):
- 2407614
- PAR ID:
- 10644091
- Publisher / Repository:
- Nature Portfolio
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 15
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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