Abstract: Polar zooplanktons are particularly sensitive to climate change, and have been applied as ‘rapid-responders’ of climate-induced changes in this fragile ecosystem. DNA barcoding provides an alternative approach for rapid species identification of zooplanktons in southern oceans, which will accelerate the routine monitoring of zooplankton community structure. 94 specimens belonging to 32 Antarctic zooplanktons were barcoded to afford a more comprehensive reference library. An 830 to 1050 base-pair region of the mitochondrial cytochrome c oxidase subunit I (mtCOI) gene was obtained as DNA barcodes. The intraspecific variation of the gene ranged from 0 to 2.6% (p-distance), with the average of 0.67% (SD=0.67%). Meanwhile, the counterpart between species within the same genera ranged from 0.1% (Calanus) to 29.3% , with the average of 15.3% (SD=8.4%). The morphological and genetic similarities between C. propinquus and C. simillimus raise new questions about the status of C. simillimus as a different species. Except for the two Calanus species (C. propinquus and C. simillimus), the intraspecific genetic divergence was much smaller than interspecific divergence among congenus species, confirming the existence of barcode gap for Antarctic zooplanktons. In addition, species rather than Calanus species all grouped monophyly. Hence, DNA barcoding were confirmed as an accurate and efficient approach for zooplankton identification in the southern ocean (Species belonging to jellyfish and doliolum were not tested). Confirming evidences were also given by indicator vector analysis. The new primer sets issued here will undoubtedly facilitate the study on the species composition of Antarctic marine zooplankton by single-gene based environmental metagenomic analysis.

Key words: Southern Ocean, DNA barcode, Calanus, zooplankton