Phytoplankton photophysiology across tropical eddies: Deconvolving nutrient, light, and community signals

Abstract

Fast repetition rate fluorometry (FRRf) based on active chlorophyll fluorescence is a powerful, noninvasive tool for studying phytoplankton physiological status at high spatial and temporal resolution. The South China Sea (SCS) is one of the largest tropical–subtropical marginal seas in the world, which plays an important role in modulating regional carbon budget and climate. In this study, underway in situ FRRf measurements were carried out throughout the outer continental shelf of the northern SCS, the basin of the northern SCS, the cyclonic eddy influenced domain in the western SCS, and the basin of the southeastern SCS. Pronounced diurnal variability of FRRf-derived parameters were observed, characterized by a large midday depression and slight nocturnal depression of the maximum quantum yield of photosystem II (Fv/Fm) and a slight increase in the functional absorption cross-section of photosystem II photochemistry (σPSII) at noon. Fv/Fm at the surface was typically as low as 0.1–0.3 and exhibited higher values (~0.4) where internal waves occurred. The cyclonic eddy increased Fv/Fm slightly, implying that it had a limited impact on surface phytoplankton photophysiology. With proper interpretation, FRRf has been a powerful tool to assess the physiological status of phytoplankton in the sea and to correlate that to ocean dynamics in an unprecedented fine scale.

Assessing Phytoplankton Primary Productivity Variability in the Changjiang Estuary, East China Sea From Coupled Fast Repetition Rate (FRR) Fluorometry and Chlorophyll‐a Measurements

“…Specifically, Chl‐ a values are generally higher along the boundaries of Changjiang plume front compared to either coastal or offshore waters (Li et al., 2021; Figures 2e and 2f). A similar spatial pattern was observed for F v / F m values when all data were pooled, revealing a significant positive correlation between these two parameters (Spearman's Rank, r = 0.4, n = 78, p = 0.006; Figures S1 and S3 in Supporting Information )—as also observed in previous studies (Gutiérrez‐Rodríguez et al., 2020; H. Liu et al., 2022; Zhu et al., 2019). Several factors are thought to control F v / F m including the light environment, nutrient availability, and the taxonomic composition of the phytoplankton community itself (Suggett, Moore, et al., 2009).…”

Critical factors driving spatiotemporal variability in the phytoplankton community structure of the coral habitat in Dongshan Bay, China

“…River plumes and coastal upwelling systems provide rich nutrient habitats for plankton (Tong et al, 2023). The nutrient enrichment facilitated by upwelling drives alterations in the community structure of phytoplankton, biomass, physiology, size fraction, and other relevant parameters (Wang et al, 2016;Du and Peterson, 2018;Yang et al, 2019;Liu et al, 2022;Mo et al, 2023).…”

Seasonal variability of satellite-derived primary production in the South China Sea from an absorption-based model

“…In summary, the seasonality of NPP is influenced by a variety of environmental dynamics, but it fundamentally depends on the combined regulation of light conditions, nutrient concentration, and CHL concentration. In the future, as studies of the physiological state and vertical structures of phytoplankton deepens, estimation of NPP with more accurate size-fractionated models were expected to improve this understanding (Sathyendranath et al, 2020;Liu et al, 2022;Deng et al, 2022).…”