[B-CG05] Diversity and ecology of marine protists -from past to present

[BCG05-P04] Temporal variation of molecular-based biological communities in particulate organic matter in the northwestern Pacific

*Ayumi Maeda¹, Miyuki Nishijima¹, Akira Iguchi¹, Atsushi Suzuki¹, Syunsuke Kondo², Jumpei Minatoya³ (1.Geological Survey of Japan, 2.KANSO TECHNOS CO., LTD., 3.Japan Organization for Metals and Energy Security (JOGMEC))

Keywords:Sediment-trap experiment, sinking particles, environmental DNA, protist

Organic matter produced in the surface ocean is crucial in the transport of carbon to the deep ocean as part of oceanic carbon cycling. Previously, settling particles have been collected directly using sediment traps, which have helped to elucidate monthly/yearly quantitative and qualitative fluctuation of particles and mechanisms of temporal change. However, little is known about the biological composition and origin of settling particles that reach the abyssal ocean. In this study, we performed high-throughput sequence analyses of the microbial community based on DNA extracted from bulk sediment-trap samples preserved with Lugol solution. To investigate seasonal variation, a one-year sediment trap was moored at approximately 4700 m depth in the Northwest Pacific from August 2021 to July 2022. The 16S rRNA gene sequence-based results show a dominance of Gammaproteobacteria and Alphaproteobacteria. The relative proportions of Cyanobacteria and chloroplasts from Chlorophyta exhibit two peaks (August to November 2021 and July 2022), and a minimum from December 2021 to March 2022. This trend roughly corresponds to the total flux of particulate matter and the patterns of the relative proportion of Chlorophyta in the 18S rRNA gene-sequence-based Eukaryota community. In addition to Chlorophyta, Protists and Metazoa are the dominant eukaryotes, and Metazoa, mostly Hydrozoa and Gastropoda, were sporadically abundant. From December 2021 to March 2022, the relative proportions of Cercozoa and Ciliates increased, with a minimum of Chlorophyta. The DNA-based biological communities are divided into two clusters (summer–fall and winter–spring) related to the abundance of surface primary production.