Surf-diatoms from sandy beaches on the Eastern Coast of South America (Brazil): the identification of Anaulus Ehrenberg and Asterionellopsis Round

“Surf diatoms” can form high biomass in the surf zone of sandy beaches around the world, Asterionellopsis and Anaulus being the main genera of this group in Brazil. Asterionellopsis glacialis was considered a cosmopolitan species, and taxonomic studies using molecular and morphological tools showed that A. glacialis is a complex with cryptic and semicryptic species. So, it would be plausible to suppose that Anaulus australis , another surf zone patch-forming diatom with wide latitudinal occurrence could also be part of a species complex. We collected and identified Anaulus and Asterionellopsis strains from tropical, subtropical and warm temperate sandy beaches on the east coast of South America (Brazil) based on genetic divergence, phylogeny, single-locus automated species delimitation methods (both genera), and frustule ultrastructure ( Anaulus ). Anaulus and Asterionellopsis showed contrasting diversity patterns and spatial distribution: a single species of Anaulus australis was registered in tropical and subtropical beaches, while at least three species of Asterionellopsis : A. tropicalis , A. thurstonii and A. guyunusae were observed at different latitudes, indicating that Asterionellopsis species have distinct ecological requirements. Asterionellopsis thurstonii was previously reported in Europe and it is documented here for the first time in the Southern Hemisphere. The different diversity patterns between these two surf diatom genera suggest that they are likely to have distinct ages, and dispersion and/or speciation processes.