Sediment Trap Study Reveals Dominant Contribution of Metazoans and Dinoflagellates to Carbon Export and Dynamic Impacts of Microbes in a Subtropical Marginal Sea

Flux and efficiency of carbon export in the ocean has been widely studied using sediment traps, but due to limitations of traditional methods, differential contribution of different organisms is poorly understood. Here, we used DNA metabarcoding to document taxonomic composition for sediment traps deployed at a continental shelf (C6) and a continental slope (C9) site in the South China Sea. The results indicated that metazoans (mainly copepods) and dinoflagellates were the most dominant contributors overall, while dinoflagellates, diatoms, and haptophytes dominated the photosynthetic assemblage. For prokaryotes, Gammaproteobacteria dominated all samples. Furthermore, comparing the trap flora to overlying plankton revealed that metazoans and Polycystinea from Eukaryota and Gammaproteobacteria and Bacteroidetes from Prokaryota were enriched in the trap at both stations whereas haptophytes and Dinophyceae were consistently attenuated during sinking. In addition, Oceanospirillaceae and Rhodobacteraceae exhibited negative correlations with dinoflagellates, and based on overlying plankton metatranscriptomes, were most transcriptionally active lineages for metabolizing labile and semi-labile organic carbon, potentially contributing to the Martin's decay of sinking particulate organic carbon. Using DNA and RNA sequencing technologies, this study provides novel insights into the lineage-specific contribution and dynamic impacts of microbes to carbon export in a subtropical marginal sea.