Protist communities in a marine oxygen minimum zone off Costa Rica by 454 pyrosequencing

Abstract

<p><strong>Abstract.</strong> Marine planktonic protists, including microalgae and protistan grazers, are an important contributor to global primary production and carbon and mineral cycles, however, little is known about their population shifts along the oxic-anoxic gradient in the water column. We used 454 pyrosequencing of the 18S rRNA gene and gene transcripts to study the community composition of whole and active protists throughout a water column in the Costa Rica Dome, where a stable oxygen minimum zone (OMZ) exists at a depth of 400~700 m. A clear shift of protist composition from photosynthetic <i>Dinoflagellates</i> in the surface to potential parasitic <i>Dinoflagellates</i> and <i>Ciliates</i> in the deeper water was revealed along the vertical profile at both rRNA and rDNA levels. Those protist groups recovered only at the rDNA level represent either lysed aggregates sinking from the upper waters or potential hosts for parasitic groups. UPGMA clustering demonstrated that total and active protists in the anoxic core of OMZ (550 m) were distinct from those in other water depths. The reduced community diversity and presence of a parasitic/symbiotic trophic lifestyle in the OMZ, especially the anoxic core, suggests that OMZs can exert a selective pressure on protist communities. Such changes in community structure and a shift in trophic lifestyle could result in a modulation of the microbial loop and associated biogeochemical cycling.</p>

Marked changes in diversity and relative activity of picoeukaryotes with depth in the global ocean

“…Yet, protist distributions in OMZ are largely unknown. Our results indicated that the alpha diversity found in OMZ in the Pacific Ocean is similar to that of epipelagic waters, as observed by Jing et al (2015), indicating a relatively high diversity in hypoxic waters. The most 400 abundant groups in the OMZ retrieved with the rRNA were Chrysophyceae, Ciliates and Dinoflagellates.…”

“…The most 400 abundant groups in the OMZ retrieved with the rRNA were Chrysophyceae, Ciliates and Dinoflagellates. The presence of Chrysopyceae in the OMZ has been reported before (Jing et al 2015), together with that of anaerobic Ciliates (e.g. mesodiniids) and Dinoflagellates (Orsi et al 2012, Parris et al 2014, Wylezich et al 2018.…”

“…Furthermore, in regions like the eastern tropical Pacific Ocean and the tropical Indian Ocean, the mesopelagic zone contains layers with very low oxygen concentration, known as oxygen 70 minimum zones (OMZ), which play a key role in the nitrogen cycle and contain specific microbial communities (Robinson et al 2010). Protist communities in OMZ or anoxic basins have received less attention than those in oxygenated mesopelagic waters (Jing et al 2015, Orsi et al 2012, Parris et al 2014, Stoeck and Epstein 2003. Furthermore, changes in protist relative activity in the DSL or OMZ at the global scale remain unknown.…”

“…Low oxygen conditions, often found within the mesopelagic layer, can affect the community structure of protists (Jing et al 2015, Orsi et al 2012, Parris et al 2014, Wylezich et al 2018. Yet, protist distributions in OMZ are largely unknown.…”

Marked changes in diversity and relative activity of picoeukaryotes with depth in the world ocean

“…Furthermore, in regions like the eastern tropical Pacific Ocean and the tropical Indian Ocean, the mesopelagic zone contains layers with very low oxygen concentration, known as oxygen minimum zones (OMZs), which play a key role in the nitrogen cycle and contain specific microbial communities [16]. However, protist communities in OMZ or anoxic basins have received less attention than those in oxygenated mesopelagic waters [17][18][19][20] and changes in protist relative activity in the DSL or OMZ at the global scale remain unknown.…”