Diversity and life-cycle analysis of Pacific Ocean zooplankton by videomicroscopy and DNA barcoding: Crustacea

Crustacea larvae and adults make up a large fraction of the biomass and number of organisms in both holoplankton (organisms that spend their entire lives in the plankton) and meroplankton (organisms that spend their larval stages in the plankton). The life cycles of these animals can be studied by raising individuals and studying them longitudinally in the laboratory, but this method can be very laborious. Here we show that DNA sequencing of a small element in the mitochondrial DNA (DNA barcoding) makes it possible to easily link life-cycle phases without the need for laboratory rearing. It can also be used to construct taxonomic trees, although it is not yet clear to what extent this barcode-based taxonomy reflects more traditional morphological or molecular taxonomy. Collections of zooplankton were made using conventional plankton nets in Newport Bay and the Pacific Ocean near Newport Beach, California, and individual crustacean specimens were documented by videomicroscopy. Adult crustaceans were collected from solid substrates in the same areas. Specimens were preserved in ethanol and sent to the Canadian Centre for DNA Barcoding at the University of Guelph, Ontario, Canada for sequencing of the COI DNA barcode. From 1042 specimens, 609 COI sequences were obtained falling into 169 Barcode Identification Numbers (BINs), of which 85 correspond to recognized species. The results show the utility of DNA barcoding for matching life-cycle stages as well as for documenting the diversity of this group of organisms.