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Abstract The ecological and oceanographic processes that drive the response of pelagic ocean microbiomes to environmental changes remain poorly understood, particularly in coastal upwelling ecosystems. Here we show that seasonal and interannual variability in coastal upwelling predicts pelagic ocean microbiome diversity and community structure in the Southern California Current region. Ribosomal RNA gene sequencing, targeting prokaryotic and eukaryotic microbes, from samples collected seasonally during 2014-2020 indicate that nitracline depth is the most robust predictor of spatial microbial community structure and biodiversity in this region. Striking ecological changes occurred due to the transition from a warm anomaly during 2014-2016, characterized by intense stratification, to cooler conditions in 2017-2018, representative of more typical upwelling conditions, with photosynthetic eukaryotes, especially diatoms, changing most strongly. The regional slope of nitracline depth exerts strong control on the relative proportion of highly diverse offshore communities and low biodiversity, but highly productive nearshore communities.
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Ecological divergence of a mesocosm in an eastern boundary upwelling system assessed with multi-marker environmental DNA metabarcoding
Abstract. Eastern boundary upwelling systems (EBUS) contribute a disproportionatefraction of the global fish catch relative to their size and are especiallysusceptible to global environmental change. Here we present the evolution ofcommunities over 50 d in an in situ mesocosm 6 km offshore of Callao, Peru, andin the nearby unenclosed coastal Pacific Ocean. The communities weremonitored using multi-marker environmental DNA (eDNA) metabarcoding and flowcytometry. DNA extracted from weekly water samples were subjected toamplicon sequencing for four genetic loci: (1) the V1–V2 region of the 16SrRNA gene for photosynthetic eukaryotes (via their chloroplasts) andbacteria; (2) the V9 region of the 18S rRNA gene for exploration ofeukaryotes but targeting phytoplankton; (3) cytochrome oxidase I (COI) forexploration of eukaryotic taxa but targeting invertebrates; and (4) the 12SrRNA gene, targeting vertebrates. The multi-marker approach showed adivergence of communities (from microbes to fish) between the mesocosm andthe unenclosed ocean. Together with the environmental information, thegenetic data furthered our mechanistic understanding of the processes thatare shaping EBUS communities in a changing ocean. The unenclosed oceanexperienced significant variability over the course of the 50 d experiment,with temporal shifts in community composition, but remained dominated byorganisms that are characteristic of high-nutrient upwelling conditions(e.g., diatoms, copepods, anchovies). A large directional change was found inthe mesocosm community. The mesocosm community that developed wascharacteristic of upwelling regions when upwelling relaxes and watersstratify (e.g., dinoflagellates, nanoflagellates). The selection ofdinoflagellates under the salinity-driven experimentally stratifiedconditions in the mesocosm, as well as the warm conditions brought about bythe coastal El Niño, may be an indication of how EBUS will respond underthe global environmental changes (i.e., increases in surface temperature andfreshwater input, leading to increased stratification) forecast by the IPCC.
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- Award ID(s):
- 1639033
- PAR ID:
- 10451652
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 20
- Issue:
- 7
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 1277 to 1298
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract In this paper we summarize improvements in climate model simulation of eastern boundary upwelling systems (EBUS) when changing the forcing dataset from the Coordinated Ocean-Ice Reference Experiments (CORE; ∼2° winds) to the higher-resolution Japanese 55-year Atmospheric Reanalysis for driving ocean–sea ice models (JRA55-do, ∼0.5°) and also due to refining ocean grid spacing from 1° to 0.1°. The focus is on sea surface temperature (SST), a key variable for climate studies, and which is typically too warm in climate model representation of EBUS. The change in forcing leads to a better-defined atmospheric low-level coastal jet, leading to more equatorward ocean flow and coastal upwelling, both in turn acting to reduce SST over the upwelling regions off the west coast of North America, Peru, and Chile. The refinement of ocean resolution then leads to narrower and stronger alongshore ocean flow and coastal upwelling, and the emergence of strong across-shore temperature gradients not seen with the coarse ocean model. Off northwest Africa the SST bias mainly improves with ocean resolution but not with forcing, while in the Benguela, JRA55-do with high-resolution ocean leads to lower SST but a substantial bias relative to observations remains. Reasons for the Benguela bias are discussed in the context of companion regional ocean model simulations. Finally, we address to what extent improvements in mean state lead to changes to the monthly to interannual variability. It is found that large-scale SST variability in EBUS on monthly and longer time scales is largely governed by teleconnections from climate modes and less sensitive to model resolution and forcing than the mean state.more » « less
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null (Ed.)Abstract. Eastern boundary upwelling systems (EBUSs) are physically and biologically active regions of the ocean with substantial impacts on ocean biogeochemistry, ecology, and global fish catch. Previous studies have used models of varying complexity to study EBUS dynamics, ranging from minimal two-dimensional (2-D) models to comprehensive regional and global models. An advantage of 2-D models is that they are more computationally efficient and easier to interpret than comprehensive regional models, but their key drawback is the lack of explicit representations of important three-dimensional processes that control biology in upwelling systems. These processes include eddy quenching of nutrients and meridional transport of nutrients and heat. The authors present the Meridionally Averaged Model of Eastern Boundary Upwelling Systems (MAMEBUS) that aims at combining the benefits of 2-D and 3-D approaches to modeling EBUSs by parameterizing the key 3-D processes in a 2-D framework. MAMEBUS couples the primitive equations for the physical state of the ocean with a nutrient–phytoplankton–zooplankton–detritus model of the ecosystem, solved in terrain-following coordinates. This article defines the equations that describe the tracer, momentum, and biological evolution, along with physical parameterizations of eddy advection, isopycnal mixing, and boundary layer mixing. It describes the details of the numerical schemes and their implementation in the model code, and provides a reference solution validated against observations from the California Current. The goal of MAMEBUS is to facilitate future studies to efficiently explore the wide space of physical and biogeochemical parameters that control the zonal variations in EBUSs.more » « less
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Variability in community composition is often attributed to underlying differences in physical environments. However, predator–prey interactions can play an equally important role in structuring communities. Although environmental differences select for different species assemblages, less is known about their impacts on trait compositions. We develop a trait-based analysis of plankton communities of the southern California Current System across multiple trophic levels, from bacteria to mesozooplankton, and over a gradient of environmental conditions, from the oligotrophic open ocean to coastal upwelling. Across a factor of four differences in total community biomass, we observe similarities in the size structure along the environmental gradient, with the most pronounced departures from proportional variations in the biomasses found in the largest protists (> 40 lm). Differences in the trait distributions emerge within a small range of size groups: greater biomass contribution of larger autotrophs (> 10 lm) is observed only for the upwelling region.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-20-1277-2023
