Assessing the trophic ecology of Southern Ocean Myctophidae: the added value of DNA metabarcoding

Lanternfishes (Myctophidae) are key components of mesopelagic fish communities globally. In the Southern Ocean, incomplete information on myctophid diets limits our understanding of their energetics, interactions, and wider ecosystem impact. Traditional microscopic methods of diet analysis have relatively coarse prey resolution and possible taxonomic and observer biases. Deoxyribonucleic acid (DNA) metabarcode sequencing promises higher taxonomic and temporal resolution, but uncertainty remains in comparing this with microscopy-based analyses. Here, we applied 18S DNA metabarcode sequencing to stomach contents from 20 Electrona antarctica individuals that had previously been examined via microscopic analysis. Across all fish analysed, crustacean and gastropod taxa dominated the prey identified via both methods, with broad agreement between methods on the relative abundance of different prey items. DNA metabarcode sequencing recovered greater taxonomic diversity and resolution, particularly for soft-bodied prey items and small crustaceans. DNA sequencing results also more clearly differentiated diet between individuals collected from different environments. Overall, our findings illustrate how DNA-based methods are complementary to, and consistent with, traditional methods and can provide additional, high-resolution data on a range of trophic interactions.