[B-CG07] Frontier in Biology and Paleobiology of Fossilized Micro-organisms

[BCG07-10] Fidelity of symbiotic Dinoflagellate diversity of large benthic foraminifera in severe shallow-reefs compared to deep-reefs

*Ayumi Maeda^1,2, Kohei Hamamoto^3,2, Miyuki Nishijima², Akira Iguchi², Atsushi Suzuki² (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Geological Survey of Japan, 3.Ehime University, Center for Marine Environmental Studies)

Keywords:Large benthic foraminifera, Foraminifera, Coral reef, Symbiodiniaceae, DNA metabarcoding, symbiont relationship

Symbiotic relationships between dinoflagellates of the family Symbiodiniaceae and other marine organisms support coral reef ecosystems. Reef-dwelling, large, benthic foraminifers contribute to reef substrate formation. Although foraminifera of the subfamily Soritinae host dinoflagellates of the family Symbiodiniaceae to form unique relationship, the diversity of dinoflagellates that establish symbiotic relationships with soritids and their spatial and population-level variation are not yet understood. Here, we investigated diversity of the mutualistic dinoflagellate community in Amphisorus kudakajimensis collected from nine sites at different depths in three reef locations on Akajima Island, and a single depth at Odo in Okinawa Island, Okinawa, Japan. Seawater samples in a sampling site in Odo were also collected to compare Symbiodiniaceae communities in environmental samples to those in A. kudakajimensis. Next-generation sequencing technology and the SymPortal pipeline specific to analyses of internal transcribed spacer region 2 of the ribosomal RNA gene of Symbiodiniaceae yielded 39 lineages in 154 specimens. Dominant lineages were Cladocopium, Freudenthalidium, and Halluxium, and multiple lineages comprised the dinoflagellate community in a single specimen. Halluxium was dominant in deep communities (>9 m) at Akajima, whereas it was not detected in shallow populations (< 2 m). In seawater samples in Odo, major lineages were Symbiodinium, Durusdinium, and Cladocopium which is different from symbionts of A. kudakajimensis. Freudenthalidium, Halluxium, and Cladocopium related to Soritinae were not dominant among free-living Symbiodiniaceae found in seawater and sediment samples in coral reefs in literature. Thus, Symbiodiniaceae community in A. kudakajimensis may be stable and isolated from surrounding free-living Symbiodiniaceae, despite host has potential flexibility of Symbiodiniaceae communities. Symbiodiniaceae diversity was greater in the eight deep populations than in the two shallow populations. Specific combinations of Cladocopium and Freudenthalidium in A. kudakajimensis under large environmental fluctuations of the shallow reef suggest that symbiont communities converge in low-diversity combinations to adapt to severe environments in shallow water, exposed to high UV light intensity. Our results provide insights into possible host-symbiont adaptation patterns to future climate change.