[B-CG05] Frontier in diversity and ecology of protists and microfossils

[BCG05-P02] Detection of spinose species and dominance of microperforate species in molecular community of planktic foraminifers in the northwestern Pacific seamounts

*前田 歩^1,2、西島 美由紀²、井口 亮²、鈴木 淳²、近藤 俊祐³、鴨志田 紘子⁴ (1.東京大学　大気海洋研究所、2.産業技術総合研究所　地質調査総合センター、3.株式会社KANSOテクノス、4.独立行政法人 エネルギー・金属鉱物資源機構)

キーワード：セジメントトラップ、有孔虫、環境DNA、堆積物DNA、海山

Foraminifera is single-celled organism living in widespread environments and a good indicator of environmental change with species forming calcareous shells. High-throughput sequencing of foraminiferal DNA in environmental samples is an ideal technique for understanding the characteristics of foraminiferal community in various environments. In addition, molecular community of planktic foraminifera has potential to evaluate a seasonal change of community structure comparing to test assemblages of planktic foraminifera. In this study, we analyzed sinking particles collected by sediment trap at approximately 4700 m depth in Zhinyu Guyot in the northwestern Pacific to investigate seasonal variation from August 2021 to July 2022. In addition, seawater and sediment samples collected in July were analyzed to evaluate species-specific persistence of DNA. In sediment trap samples, fourteen morphospecies of planktic foraminifera was detected using existing universal primers of s14f3-s17. Candeina nitida and Globigerinita glutinata dominated the community of planktic foraminifers in all samples. The dataset showed decreases of species richness from December to March and increases of species richness from April to July. From April to July, increases of total organic carbon in sinking particles and proportions of phytoplankton sequences suggest that primary production was activated, which may support increases of standing stocks of various planktic foraminifera. Seawater and sediment samples indicated the dominance of C. nitida and G. glutinata in addition to subsurface-dwelling species, which could be caused by species-specific preferences for PCR amplification using existing universal primers for foraminifera. Sequences of benthic foraminifers were identified in bottom water samples due to resuspended particles. However, we failed to detect foraminifers using surface seawater because of mismatches of primers to surface-dwelling spinose species. As a result, the important species such as Trilobatus sacculifer and Globigerinoides ruber are hardly detected, while microperforate species show large proportions in molecular community. We proposed a new primer set targeting mainly for spinose species including T. sacculifer and G. ruber to reduce the difference between foraminiferal test and molecular community. The new primer set, s14p-env and perv3f-env, is based on existing primers for spinose species, s14p and perv3f. The results of HTS of sediment trap samples showed the new primer set successfully detected T. sacculifer, Turborotalita quinqueloba, Globorotalia truncatulinoides, and Globoquadrina conglomerata.