Thaliaceans are pivotal gelatinous zooplankton that accelerate carbon export and structure pelagic food webs through rapid filtration and production of dense fecal pellets and carcasses. While taxon-specific contributions to the biological pump are recognized, their ecological niches and drivers of distribution remain poorly resolved. Here, we analyzed a unique five-year dataset (2007–2011) from annual surveys in the northern South China Sea, spanning contrasting hydrographic regimes shaped by the Pearl River plume, Yuedong upwelling, and Taiwan Bank upwelling.
The results revealed clear basin-scale niche partitioning between doliolids and salps, providing the first multi-year baseline for how thaliaceans respond to monsoon-driven variability in a marginal sea. Doliolids dominated high-chlorophyll a environments linked to river discharge and upwelling. In contrast, salps thrived in high-salinity, moderate-chlorophyll a offshore waters. Hierarchical partitioning analysis of the RDA results indicated that this distribution pattern was primarily driven by sea surface salinity, followed by sea surface chlorophyll a concentration. Interannual comparisons further showed that monsoon-driven precipitation modulated community structure: wet years expanded doliolid habitats through freshwater discharge, whereas droughts favored salp dominance through offshore seawater intrusion.
By linking hydroclimatic forcing to thaliacean biogeography, this study provides a basis for understanding potential ecosystem responses to climate variability. The findings suggest that changes in rainfall patterns can influence thaliacean community composition, which may, in turn, modulate carbon-export processes in monsoon-driven marginal seas. These results offer new perspectives on the connections between hydroclimatic variability and plankton-mediated biogeochemical cycles.
 

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