What goes in, must come out: Evaluation of the DNA metabarcoding approach to analyse diet of threatened seahorses

Seahorses are considered flagship species of the conservation efforts. Indeed, due to the worldwide decline of local populations during the last decades, all seahorse species were listed on the IUCN Red List and Appendix II of CITES. Because of the threatening status, improving knowledge of their dietary composition, while using a non-invasive approach, might be of great importance. Starting from faecal samples of the European seahorse Hippocampus guttulatus collected during feeding trials, we used, for the first time on these fish, metagenomic amplicon-based HTS (High Throughput Sequencing) approach. The findings indicated the reliability of the present molecular approach, allowing the characterization of the effectively ingested prey. Unlike traditional methods on faecal samples, this technique can identify items that might not leave solid remains. As only a small amount of starting faecal material is needed and the sampling procedure is neither invasive nor lethal, DNA metabareoding appears to be useful in the investigation on threatened seahorse diet and, in future, could help to define management and conservation actions.