Temporal changes in the structure of protist communities incubated under normoxic and hypoxic conditions: a metabarcoding analysis

다국어 초록 (Multilingual Abstract)

Hypoxia often causes the large-scale mortality of benthic organisms and alters the structure and function of pelagicand benthic communities. Protists are a major component of pelagic and benthic communities. Using a metabarcodinganalysis, we explored the temporal changes in the structure of protist communities incubated for seven days under normoxic(7.0 mg L-1) and hypoxic (1.5 mg L-1) conditions. The incubated water was originally collected from Tongyeong Bay,Korea, where hypoxia frequently occurs. Among the phyla, the relative amplicon sequence variant (ASV) abundance ofCercozoa and Ochrophyta increased under hypoxia from day 0 to day 7, whereas that of other phyla declined or remainedsimilar. Moreover, the relative ASV abundances in the phylum Dinoflagellata under both oxygen conditions were higheston days 0, 3, and 7. Among the dinoflagellate orders, the highest dinoflagellate ASV abundance under hypoxia on day7 belonged to the order Peridiniales, whereas the highest relative read abundance belonged to Prorocentrales. The 35dinoflagellate species that were detected under the hypoxic condition during incubation were autotrophic (two), phototrophic(autotrophic or mixotrophic) (15), mixotrophic (eight), kleptoplastidic (one), heterotrophic (eight), and parasitic(one), indicating that dinoflagellates with diverse trophic modes are present under hypoxia. Of these detected dinoflagellatespecies, 14 were present under the hypoxia on day 7. Furthermore, 19 dinoflagellate species were newly determinedto be present under hypoxia, 6 of which were present on day 7. These findings highlight the ecological resilience andadaptability of protist communities under the hypoxic condition. The present study provides insights into the potentialroles of protists in maintaining ecosystem functions in the oxygen-depleted environments.