High genetic diversity and novelty in planktonic protists inhabiting inland and coastal high salinity water bodies

We analyzed the genetic diversity (18 S r RNA gene) of planktonic microbial eukaryotes in 34 different coastal and inland saline ponds. A wide range of environmental conditions was covered with up to 30‐fold differences in salinity concentrations (12.5–384 g L −1 ), and in situ temperatures (1.3–37.5 °C), and three orders of magnitude in the trophic status (i.e. chlorophyll a  <   0.1 to >50 mg L −1 ). Geographically distant sites were studied with contrasting salt origins, and different temporal patterns of wetting and drying. The genetic diversity was high, far beyond the few groups traditionally considered as high salinity‐adapted, with sequences spread throughout eight high‐rank taxonomic groups and 27 eukaryal classes. The novelty level was extremely high, with 10% of the whole dataset showing < 90% identity to any previously reported sequence in G en B ank. Opisthokonta and R hizaria contained the highest novelty and C hlorophyta and A lveolata the lowest. Low identity sequences were observed both in coastal and inland sites and at lower and at higher salinities, although the degree of novelty was higher in the hypersaline waters (> 6.5% salinity). Overall, this study shows important gaps in the current knowledge about protists inhabiting continental (hyper)saline water bodies, highlighting the need for future, more detailed investigations.