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

Abstract

Hypoxia often causes the large-scale mortality of benthic organisms and alters the structure and function of pelagic and bendiic communities. Protists are a major component of pelagic and bendiic communities. Using a metabarcoding analysis, 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 I/1) conditions. The incubated water was originally collected from Tongyeong Bay, Korea, where hypoxia frequently occurs. Among die phyla, die relative amplicon sequence variant (ASV) abundance of Cercozoa and Ochrophyta increased under hypoxia from day 0 to day 7, whereas that of odier phyla declined or remained similar. Moreover, the relative ASV abundances in die phylum Dinoflagellata under both oxygen conditions were highest on days 0, 3, and 7. Among die dinoflagellate orders, die highest dinoflagellate ASV abundance under hypoxia on day 7 belonged to die order Peridiniales, whereas die highest relative read abundance belonged to Prorocentrales. The 35 dinoflagellate species diat were detected under the hypoxic condition during incubation were autotrophic (two), photo-trophic (autotrophic or mixotrophic) (15), mixotrophic (eight), kleptoplastidic (one), heterotrophic (eight), and parasitic (one), indicating diat dinoflagellates wfth diverse trophic modes are present under hypoxia. Of diese detected dinoflagellate species, 14 were present under die hypoxia on day 7. Furthermore, 19 dinoflagellate species were newly determined to be present under hypoxia, 6 of which were present on day 7. These findings highlight die ecological resilience and adaptability of protist communities under die hypoxic condition. The present study provides insights into die potential roles of protists in maintaining ecosystem functions in die oxygen-depleted environments.