Biogeography of six species in the planktonic diatom genus Bacteriastrum (Bacillariophyta)

ABSTRACT

Marine planktonic diatom species can exhibit contrasting distribution patterns, from endemic to cosmopolitan. Endemicity is counter-intuitive for planktonic species given their potentially large population sizes and ample migration opportunities by means of ocean currents. Here, we analyse the biogeography of six species of the diatom genus Bacteriastrum with apparently contrasting distribution patterns. Occurrence data obtained from metabarcode reads in samples from Ocean Sampling Day (OSD) sites and from Tara Oceans stations as well as from their observational records included in biodiversity data repositories of GBIF and OBIS were plotted in occurrence maps. According to metabarcoding data, the six species examined here occur all over the temperate and tropical parts of the oceans. Observational records corroborate this finding for B. elegans, B. furcatum, B. hyalinum and B. mediterraneum. Instead, atypical colony former B. jadranum is encountered at just a few distant sites, and solitary B. parallelum only in the Gulf of Naples. The metabarcoding data reveal that the latter two species are far more widely distributed than their actual sightings according to GBIF and OBIS, and that B. hyalinum also occurs in the Arctic. The most likely reasons for the discrepancies among the different data sources are the relatively recent description of B. jadranum and B. parallelum, their diminutive and inconspicuous habitus, and their possible misidentification in routine plankton counting.

HIGHLIGHTS

• Metabarcoding data of Tara Oceans and OSD discern Bacteriastrum species.• Pan-oceanic distribution of Bacteriastrum species according to global metabarcoding data.• Distribution patterns of phytoplankton species can be inferred from global metabarcode datasets.

Keywords:

• Bacteriastrum
• distribution
• GBIF
• metabarcoding
• OBIS
• Ocean Sampling Day
• phytoplankton
• Tara Oceans

Acknowledgements

We thank the Tara Oceans consortium for access to datasets prior to their free availability.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2021.2021591

Supplementary fig. S1. Occurrence of Bacteriastrum species in metabarcoding datasets. A) OSD; B) Tara Oceans. Blue and red circles indicate presence in OSD and Tara Oceans data respectively; orange crosses indicate absence.Supplementary fig. S2. Approximately-maximum-likelihood phylogenetic tree of 18S-V4 metabarcodes ≥ 99% similar to the Bacteriastrum reference V4 sequences (Table 1), gathered from the OSD metabarcodes. Size of triangles is proportional to number of reads. Values at nodes indicate support using the Shimodaira-Hasegawa test. Metabarcode reads were collapsed and only the position of the reference barcode was reported.Supplementary fig. S3. Approximately-maximum-likelihood phylogenetic tree of 18S-V9 metabarcodes ≥ 99% similar to Bacteriastrum reference V9 sequences (Table 1), gathered from the Tara Oceans metabarcodes. Size of triangles is proportional to number of reads. Values at nodes indicate support using the Shimodaira-Hasegawa test. Metabarcode reads were collapsed and only the position of the reference barcode was reported.

Author contributions

R. Piredda: design and execution of data analysis, map production and manuscript editing; D. De Luca: design and execution of data analysis, map production and manuscript editing; D. Sarno: original concept, data comparison, manuscript drafting and editing; W.H.C.F. Kooistra: original concept, data comparison, manuscript drafting and editing.

Additional information

Funding

DDL was supported by a PhD fellowship funded by the Stazione Zoologica Anton Dohrn (Open University – SZN PhD Programme). WHCFK acknowledges funding from the EU project ASSEMBLE Plus (GA 730984).