Microbial tropicalization driven by a strengthening western ocean boundary current

Lauren F. Messer, Martin Ostrowski, Martina A. Doblin, Katherina Petrou, Mark E. Baird, Timothy Ingleton, Andrew Bissett, Jodie Van de Kamp, Tiffanie Nelson, Ian Paulsen, Levente Bodrossy, Jed A. Fuhrman, Justin R. Seymour, Mark V. Brown*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    3 Citations (Scopus)

    Abstract

    Western boundary currents (WBCs) redistribute heat and oligotrophic seawater from the tropics to temperate latitudes, with several displaying substantial climate change-driven intensification over the last century. Strengthening WBCs have been implicated in the poleward range expansion of marine macroflora and fauna, however, the impacts on the structure and function of temperate microbial communities are largely unknown. Here we show that the major subtropical WBC of the South Pacific Ocean, the East Australian Current (EAC), transports microbial assemblages that maintain tropical and oligotrophic (k-strategist) signatures, to seasonally displace more copiotrophic (r-strategist) temperate microbial populations within temperate latitudes of the Tasman Sea. We identified specific characteristics of EAC microbial assemblages compared with non-EAC assemblages, including strain transitions within the SAR11 clade, enrichment of Prochlorococcus, predicted smaller genome sizes and shifts in the importance of several functional genes, including those associated with cyanobacterial photosynthesis, secondary metabolism and fatty acid and lipid transport. At a temperate time-series site in the Tasman Sea, we observed significant reductions in standing stocks of total carbon and chlorophyll a, and a shift towards smaller phytoplankton and carnivorous copepods, associated with the seasonal impact of the EAC microbial assemblage. In light of the substantial shifts in microbial assemblage structure and function associated with the EAC, we conclude that climate-driven expansions of WBCs will expand the range of tropical oligotrophic microbes, and potentially profoundly impact the trophic status of temperate waters.

    Original languageEnglish
    Pages (from-to)5613-5629
    Number of pages17
    JournalGlobal Change Biology
    Volume26
    Issue number10
    DOIs
    Publication statusPublished - Oct 2020

    Keywords

    • East Australian Current
    • microbial community
    • microbial indicators
    • ocean boundary currents
    • tropicalization

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