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Abstract The Hawaii Ocean Time‐series (HOT) at Station ALOHA (22.75°N, 158°W) in the North Pacific Subtropical Gyre (NPSG) serves as a critical vantage point for observing plankton biomass production and its ecological implications. However, the HOT program's near‐monthly sampling frequency does not capture shorter time scale variability in phytoplankton populations. To address this gap, we deployed the SeaFlow flow cytometer for continuous monitoring during HOT cruises from 2014 to 2021. This approach allowed us to examine variations in the surface abundance and cell carbon content of specific phytoplankton groups: the cyanobacteriaProchlorococcus,Synechococcus, andCrocosphaeraas well as a range of small eukaryotic phytoplankton ( 5 μm). Our data showed that daily to monthly variability inProchlorococcusandSynechococcusabundance matches seasonal and interannual variability, while small eukaryotic phytoplankton andCrocosphaerashowed the highest seasonal and interannual fluctuations. The study also found that eukaryotic phytoplankton andCrocosphaerahad higher median cellular growth rates (0.076 and , respectively) compared toProchlorococcusandSynechococcus(0.037 and , respectively). These variances in abundance and growth rates indicate that shifts in the community structure significantly impact primary productivity in the NPSG. Our results underscore the importance of daily to monthly phytoplankton dynamics in ecosystem function and carbon cycling.
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A single Prochlorococcus ecotype dominates the tropical Bay of Bengal with ultradian growth
The Bay of Bengal (BoB) spans >2.2 million km2in the northeastern Indian Ocean and is bordered by dense populations that depend upon its resources. Over recent decades, a shift from larger phytoplankton to picoplankton has been reported, yet the abundance, activity, and composition of primary producer communities are not well‐characterized. We analysed the BoB regions during the summer monsoon.Prochlorococcusranged up to 3.14 × 105cells mL−1in the surface mixed layer, averaging 1.74 ± 0.46 × 105in the upper 10 m and consistently higher thanSynechococcusand eukaryotic phytoplankton. V1‐V2 rRNA gene amplicon analyses showed the High Light II (HLII) ecotype formed 98 ± 1% ofProchlorococcusamplicons in surface waters, comprising six oligotypes, with the dominant oligotype accounting for 65 ± 4% of HLII. Diel sampling of a coherent water mass demonstrated evening onset of cell division and rapidProchlorococcusgrowth between 1.5 and 3.1 div day−1, based on cell cycle analysis, as confirmed by abundance‐based estimates of 2.1 div day−1. Accumulation ofProchlorococcusproduced by ultradian growth was restricted by high loss rates. Alongside prior Arabian Sea and tropical Atlantic rates, our results indicateProchlorococcusgrowth rates should be reevaluated with greater attention to latitudinal zones and influences on contributions to global primary production.
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- Award ID(s):
- 2230811
- PAR ID:
- 10543767
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Environmental Microbiology
- Volume:
- 26
- Issue:
- 3
- ISSN:
- 1462-2912
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/1462-2920.16605
