Abstract
The ecology and distribution of green phytoplankton (Chlorophyta) in the ocean is poorly known because most studies have focused on groups with large cell size such as diatoms or dinoflagellates that are easily recognized by traditional techniques such as microscopy. The Ocean Sampling Day (OSD) project sampled surface waters quasi-simultaneously at 141 marine locations, mostly in coastal waters. The analysis of the 18S V4 region OSD metabarcoding dataset reveals that Chlorophyta are ubiquitous and can be locally dominant in coastal waters. Chlorophyta represented 29% of the global photosynthetic reads (Dinoflagellates excluded) and their contribution was especially high at oligotrophic stations (up to 94%) and along the European Atlantic coast. Mamiellophyceae dominated most coastal stations. At some coastal stations, they were replaced by Chlorodendrophyceae, Ulvophyceae, Trebouxiophyceae or Chlorophyceae as the dominating group, while oligotrophic stations were dominated either by Chloropicophyceae or the uncultured prasinophytes clade IX. Several Chlorophyta classes showed preferences in terms of nitrate concentration, distance to the coast, temperature and salinity. For example, Chlorophyceae preferred cold and low salinity coastal waters, and prasinophytes clade IX warm, high salinity, oligotrophic oceanic waters.
Highlights
Marine waters are inhabited by a heterogeneous assemblage of organisms that includes a large diversity of unicellular eukaryotes
Some stations located near oceanic islands such as OSD7 (Moorea - Tiahura) in French Polynesia corresponded to truly oceanic waters
Still it offers an opportunity to gain insights into the contribution and distribution of Chlorophyta classes in marine coastal waters. It highlights that Chlorophyta can be the main photosynthetic group in some ecosystems
Summary
Marine waters are inhabited by a heterogeneous assemblage of organisms that includes a large diversity of unicellular eukaryotes (protists). Photosynthetic organisms are divided into two lineages, green and red The former originates from primary endosymbiosis and includes Chlorophyta[1], the major green algal group in marine waters, as well as vascular plants. The latter has undergone secondary and even tertiary endosymbioses and is represented among other by diatoms and dinoflagellates that are key photosynthetic producers in productive marine waters. Differences in the distribution of major classes or clades have already been demonstrated between coastal and oceanic waters. We analyze the OSD V4 metabarcoding datasets with the aim to describe the distribution of the major classes of Chlorophyta in the global coastal ocean
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