Planktonic bivalve larvae identification and quantification in Gomso Bay, South Korea, using next-generation sequencing analysis and microscopic observations

Abstract

Planktonic larval stages of bivalves are notoriously difficult to identify due to their similar morphology. To evaluate changed patterns in the presented planktonic bivalve larvae within Gomso Bay (Yellow Sea, South Korea), three sites were sampled twice a month from June to October 2015 and were analysed using next-generation sequencing (NGS) and light microscopy. Bivalve larvae revealed different patterns, and at least five bivalve taxa were only detected by the NGS. According to the NGS results, most bivalve larvae were Crassostrea gigas (37%), followed by Ruditapes philippinarum (26%), and Solen strictus (23%); Mactra chinensis and M. veneriformis accounted for <1% of the bivalve larvae. C. gigas and S. strictus were most abundant in late June, but rare in the other investigated periods, while R. philippinarum was more abundant in June and late September. Microscopic observations showed a similar trend to the NGS in terms of bivalve larvae presence, although they were difficult to identify the exact species. Thus, morphological and molecular approaches should be combined in future studies to provide accurate sequences of correctly identified specimens to develop NGS libraries.