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What’s in your ballast water? Oversampling and DNA metabarcoding reveal deep diversity in a single tank
Citation:
Darling, J., K. Carney, P. Katrina M, AND G. Ruiz. What’s in your ballast water? Oversampling and DNA metabarcoding reveal deep diversity in a single tank. International Conference on Marine Bioinvasions, Baltimore, MD, May 15 - 19, 2023.
Impact/Purpose:
Describes utility of DNA methods for assessing diversity of organisms in ballast water, with application for understanding risk of aquatic biological invasions through ballast water transport
Description:
DNA metabarcoding is typically capable of recognizing far greater diversity in environmental samples than other methods. Here we pair this methodology with an oversampling approach to describe, as completely as possible, the diversity present in a single ballast tank. Using plankton nets with 35 µm mesh size (50 µm diagonal dimension) we collected 16 samples, 8 from each of two ballast tanks on an oil tanker arriving to the port of Valdez, Alaska. To explore differences in taxonomic diversity captured by targeting different genomic loci we utilized four primer sets, three amplifying fragments of the nuclear 18S small subunit rRNA gene and one amplifying the mitochondrial cytochrome C oxidase subunit I (COI). Our analyses reveal extraordinary diversity of operational taxonomic units (OTUs), particularly at the COI locus. Rarefaction approaches suggest that a single sample captures only approximately 20% of existing COI diversity, and that nearly 50 samples would be required to achieve 90% coverage; in contrast, all 18S loci exhibited >95% coverage in the 16 existing samples. However, while COI revealed much higher OTU diversity, 18S loci exhibited broader taxonomic coverage. Our results suggest that typical sampling events may reveal only a fraction of the diversity present in ballast tanks.
