Green microalgae in marine coastal waters: The Ocean Sampling Day (OSD) dataset

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.

A new marine prasinophyte genus alternates between a flagellate and a dominant benthic stage with microrhizoids for adhesion

“…It is clear from the environmental 18S rDNA sequences (Monier et al 2015, Tragin and Vaulot 2018, this study) that our knowledge of the biodiversity of the Mamiellophyceae is in its infancy, and that the known culture strains represent only a tiny fraction of the actual biodiversity. While pico-sized representatives (<2 lm in diameter) from the order Mamiellales dominate the biomass in many locations, and are far better known, the nano-sized representatives (2-6 lm in (1) is on the right.…”

“…The second and third data sets used the large environmental data sets available from the Ocean Sampling Day (OSD) and Tara Oceans expedition, respectively, in order to place Microrhizoidea pickettheapsiorum in the context of the larger diversity of Mamiellophyceae observed in these global environmental surveys using culture-independent high-throughput sequencing, Operational taxonomic units (OTUs) sequences from OSD classified as Dolichomastigaceae (Tragin and Vaulot 2018), and OTUs from Tara Oceans (Bork et al 2015) classified as Mamiellales or Dolichomastigales (Monier et al 2016) were used to produce phylogenies. OSD and Tara Oceans used different regions of the 18S rRNA, and therefore they were analysed separately.…”

“… Figure S3. Maximum likelihood phylogeny indicating the position of Microrhizoidea pickettheapsiorum in relation to Operational Taxonomic Units (OTUs) obtained from the Ocean Sampling Day survey (Tragin and Vaulot ). Ultrafast bootstratp values ≥ 95% are indicated next to tree nodes.…”

Small pigmented eukaryotes play a major role in carbon cycling in the P‐depleted western subtropical North Atlantic, which may be supported by mixotrophy

“…A culturable representative from the lineage has not yet been established. Besides their propensity for warm, low-nutrient seawaters and their pico-sized range (Shi et al 2009;Tragin and Vaulot 2018), not much is known about their biology, including nutritional mode (e.g., presence or absence of bacterivory).…”

Global distribution of Trebouxiophyceae diversity explored by high‐throughput sequencing and phylogenetic approaches

“…Trebouxiophyceae are a ubiquitous class of photosynthetic unicellular Chlorophyta (=‘green algae’) encountered in many environments, including extreme ones such as hot (Büdel et al ., ; Flechtner et al ., ; Fučíková et al ., ) and cold (Cavacini, ; Fermani et al ., ; Hodač et al ., ) deserts, or hyper acidic waters (Juárez et al ., ). They are also common in mesophilic environments like soil and continental waters, some of them can also be found in the sea (Heesch et al ., ; Tragin and Vaulot, ). But Trebouxiophyceae are mostly known for their symbiotic relationships with other organisms (Pröschold et al ., ), where they act as photobionts, providing the by‐products of their photosynthesis to the host.…”