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Metabarcoding of zooplankton diversity within the Chukchi Borderland, Arctic Ocean: improved resolution from multi-gene markers and region-specific DNA databases

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Abstract

DNA-based analyses have become powerful tools for characterizing the metazoan biodiversity of diverse marine ecosystems. Metabarcoding (i.e., large-scale taxonomic identification of complex samples via high-throughput sequencing of a DNA barcode region) frequently uses hypervariable regions of the nuclear eukaryotic 18S ribosomal RNA (rRNA) gene. However, species-level taxonomic identification is hampered by the conservative nature of the 18S gene in comparison to the mitochondrial cytochrome oxidase I (COI) barcode gene. Additionally, metabarcoding relies on reference DNA sequence databases for classification of millions of unknown sequence reads and molecular operational taxonomic units (OTUs); databases that are at present depauperate for marine zooplankton taxa. Here, we characterized the mesozooplankton community for the Chukchi Borderland (CBL) region, western Arctic Ocean, through metabarcoding analysis of the V4 and V9 hypervariable regions of 18S rRNA and a portion of COI. Characterization of zooplankton diversity for the epipelagic and upper mesopelagic layers (0–500 m) was based upon 17 metazoan taxonomic categories encompassing 24 orders in 14 classes. Taxonomic classification using the V4 and V9 markers was most reliable for orders, with copepods dominating OTU counts. To increase taxonomic resolution and allow detection of species, V4, V9, and COI OTUs were classified against DNA sequence databases for the Arctic Ocean for the subclass Copepoda. The geographic region-specific databases for 18S rRNA and COI resulted in the detection and identification of 6 genera and 49 species of copepods representing 23 families, a marked increase in the taxonomic classification of the 18S rRNA markers. The greatest copepod species diversity was captured with V4 (34 species) followed by COI (28 species) with the least copepod diversity detected by V9 (5 species). Our results demonstrate the power of using multiple gene markers, with DNA reference databases that are specific to the geographic region of interest, providing more accurate metabarcoding biodiversity measures for the copepod assemblages compared to universal metazoan sequence reference databases. Results from this study highlight the need for continued DNA barcode sequencing to increase species representation in the reference sequence databases that are crucial for accurate characterization of mesozooplankton communities.

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Acknowledgments

We gratefully thank Leocadio Blanco-Bercial (Bermuda Institute of Ocean Science) for use of his database customized from SILVA Release 132 and guidance with the Mothur pipeline. Bioinformatics were carried out using resources of the computational Biological Core, Institute of System Genomics, University of Connecticut (https://bioinformatics.uconn.edu/). We thank Bo Reese and staff at the UConn Center for Genomic Innovation (CGI) and Kendra Mass at the UConn center for Microbial Analysis, Resources, and Services (MARS) for their guidance with molecular protocols, sequencing, and bioinformatics. Many thanks to the officers and crew of the USCGC Healy and members of the scientific team, particularly Katrin Iken, Heidi Mendoza-Islas, Atsushi Yamaguchi, and Dhugal Lindsay. We would also like to thank Captain S. Schwarze, his crew of the RV Polarstern, and the chief scientist Ursula Schauer for their support during the ARK-XXVI/3 “TransArc” Polarstern cruise (PS78), 2011. We thank two peer reviewers for their comments that have helped improve the manuscript.

Funding

This work was supported by the NOAA Office of Exploration and Research under the Chukchi Borderlands: Exploration of Pelagic Life in a Complex Polar Environment project NA15OAR0110209. The work on Polarstern 2011 Arctic cruise collections that provided expertly identified specimens was performed in the framework of the state assignment of IO RAS (theme No. 0149-2019-0008) and supported by the Russian Foundation for Basic Research grants No 18-05-60158 and 19-04-00955.

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Correspondence to Jennifer M. Questel.

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The authors declare that they have no conflict of interest.

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All applicable international, national, and/or institutional guidelines for the care and use of animals were followed by the authors.

Sampling and field studies

All necessary permits for sampling and observational field studies have been obtained by the authors from the competent authorities and are mentioned in the acknowledgments, if applicable.

Data availability

The V4 and V9 nuclear 18 rRNA and mitochondrial COI metabarcoding data generated and analyzed during this study have been deposited in the NCBI GenBank Short Read Archive (https://www.ncbi.nlm.nih.gov/sra/). Raw sequence reads in FASTQ format from the NOAA Hidden Ocean 2016: Chukchi Borderland expedition can be accessed using SRA BioProject ID PRJNA593255. Eukaryotic 18S rRNA sequences were deposited in GenBank under the accession numbers MG660871-MG661071 and MN784560-MN784617. Metazoan mitochondrial COI sequences were assigned GenBank accession numbers MN831487-MN831677. Sequences for 18S and COI used to complete species representation in the ArCop databases were mined from the NCBI GenBank public repository. Bioinformatic scripts, taxonomic mapping, and corresponding FASTA sequence files formatted for Mothur for each DNA marker are available at https://github.com/JQuestel/Chukchi_Borderland_Zooplankton_Metabarcoding.

Author contributions

J.Q. conducted laboratory methods for metabarcoding, bioinformatics, created the ArCop databases, analyzed data, and wrote the manuscript. C.S., J.Q., K.K., and R.H. identified specimens used in the ArCop database. C.S., J.Q., and R.H. collected zooplankton samples used for metabarcoding analysis. H.D. sequenced 18S and COI for the ArCop databases. R.H. and A.B. acquired funding and designed the research. A.B. provided molecular ecology expertise. All authors contributed to writing the manuscript.

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Communicated by H. Stuckas

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Questel, J.M., Hopcroft, R.R., DeHart, H.M. et al. Metabarcoding of zooplankton diversity within the Chukchi Borderland, Arctic Ocean: improved resolution from multi-gene markers and region-specific DNA databases. Mar. Biodivers. 51, 4 (2021). https://doi.org/10.1007/s12526-020-01136-x

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