11:45 AM - 12:00 PM
[AOS12-10] Spatial variation of haptophyte assemblages along the Kuroshio Current: Geographical source and ecological trait
Keywords:Phytoplankton, Kuroshio, Haptophyta, East China Sea, Biodiversity
Haptophytes are one of the most abundant phytoplankton groups in the ocean, playing critical roles in marine biogeochemical and ecological processes. Their communities tend to have high diversity and stability in the environment. However, little is known about the mechanisms responsible for shaping the community structure and its associations with geographical and environmental patterns.
To reveal the community characteristics of haptophytes at the higher spatial resolution, we conducted a comprehensive observation from the upstream to downstream of the Kuroshio current during the R/V Hakuho-Maru (Japan Agency of Marine Science and Technology/ the University of Tokyo) KH-15-4 cruise in November 2015. Seawater samples for DNA analysis were collected from the surface (5 m) layer at 46 sites, filtered onto a 0.2 µm pore size filter, and stored at –80°C until analysis on land. The abundance and phylogeny of haptophytes were assessed with the real-time PCR and metabarcoding methods targeting the 18S rRNA gene, respectively. Haptophyte diversity (richness and evenness) and community composition were characterized at the amplicon sequence variant (ASV) level.
The abundance of haptophytes assessed by 18S rDNA concentration varied by over 26 folds across locations with the markedly highest value recorded at station 21, which is adjacent to the East China Sea (ECS). The richness of haptophyte ASV also increased at the same site. These results indicate a significant inflow of haptophyte community from the ECS, which comprises distinct haptophyte ASVs, into the Kuroshio region. Co-occurrence network analysis clearly separated the haptophyte ASVs into the southern Kuroshio (i.e., the upstream) and the ECS modules based on their emerging patterns. The high contribution of the ECS-derived haptophytes was first recorded at the station 21 and persisted to far downstream locations, indicating a strong influence of the ECS on the downstream Kuroshio ecosystems. We also revealed that major haptophyte ASVs, mainly composed of non-calcifying and mixotrophic lineages, can coexist among close evolutionary relatives, possibly due to their nutritional flexibility to reduce resource competition. Our results shed new light on the impact of adjacent shelf waters on the Kuroshio ecosystem.
To reveal the community characteristics of haptophytes at the higher spatial resolution, we conducted a comprehensive observation from the upstream to downstream of the Kuroshio current during the R/V Hakuho-Maru (Japan Agency of Marine Science and Technology/ the University of Tokyo) KH-15-4 cruise in November 2015. Seawater samples for DNA analysis were collected from the surface (5 m) layer at 46 sites, filtered onto a 0.2 µm pore size filter, and stored at –80°C until analysis on land. The abundance and phylogeny of haptophytes were assessed with the real-time PCR and metabarcoding methods targeting the 18S rRNA gene, respectively. Haptophyte diversity (richness and evenness) and community composition were characterized at the amplicon sequence variant (ASV) level.
The abundance of haptophytes assessed by 18S rDNA concentration varied by over 26 folds across locations with the markedly highest value recorded at station 21, which is adjacent to the East China Sea (ECS). The richness of haptophyte ASV also increased at the same site. These results indicate a significant inflow of haptophyte community from the ECS, which comprises distinct haptophyte ASVs, into the Kuroshio region. Co-occurrence network analysis clearly separated the haptophyte ASVs into the southern Kuroshio (i.e., the upstream) and the ECS modules based on their emerging patterns. The high contribution of the ECS-derived haptophytes was first recorded at the station 21 and persisted to far downstream locations, indicating a strong influence of the ECS on the downstream Kuroshio ecosystems. We also revealed that major haptophyte ASVs, mainly composed of non-calcifying and mixotrophic lineages, can coexist among close evolutionary relatives, possibly due to their nutritional flexibility to reduce resource competition. Our results shed new light on the impact of adjacent shelf waters on the Kuroshio ecosystem.