Determination of the Pacific oyster Magallana gigas (Crassostrea gigas) diet composition in two aquaculture farms by fecal DNA metabarcoding

Abstract

Fecal DNA metabarcoding is a noninvasive, accurate, rapid, and cost-effective tool to investigate diet composition. However, most fecal DNA metabarcoding studies have been conducted in mammals and birds; few have focused on marine animals, including bivalves. We performed a pilot study of the diet composition and its variation over four seasons in the Pacific oyster Magallana gigas, using eight fecal samples from two aquaculture farms, Tongyeong and Gadeokdo, in South Korea. The diversity and stability of M. gigas dietary composition were higher in Tongyeong than in Gadeokdo; they were highest in fall and lowest in winter. Taxonomic analysis identified 14 phyla, 23 classes, 43 orders, 53 families, 56 genera, and 82 species. Among them, Dinoflagellates (Dinoflagellata) and diatoms (Bacillariophyta) were predominant, together with green algae (Chlorophyta), protists (Bigyra and Cercozoa), parasites (Apicomplexa), and flatworms (Platyhelminthes) in both Tongyeong and Gadeokdo at the phylum level, based on the frequency of occurrence (FOO). High proportions of Arthropoda and Mollusca were found, indicating no selective feeding by M. gigas. At the species level, many harmful dinoflagellates were detected in both Tongyeong and Gadeokdo. In addition, there were strong similarities in the M. gigas diet composition between Tongyeong and Gadeokdo according to seasons. An additional step to cleave or block oyster DNA and avoid cross-contamination are recommended. Our findings indicated the ability of fecal DNA metabarcoding to provide qualitative and semi-quantitative information regarding the M. gigas diet, which will assist in the formulation of aquaculture management guidelines.