Progress in the analysis of english channel loliginid squid diets using DNA-metabarcoding techniques

Study of the diet of squid is hampered by the fact that these animals masticate their prey prior to ingestion and do not necessarily ingest the hard parts that allow the identification of prey remains present in the stomach. The result is a large percentage of prey in stomach contents that can be identified only according to broad categories (e.g., “teleost fish”). This is widely described in the literature and has also been found in samples from the English Channel of the two loliginid squid fished in this area (Loligo forbesii and Loligo vulgaris). New biological samples of both species were collected at the Port-en-Bessin fish market during the 2019–2020 fishing season. Stomach contents were studied through DNA metabarcoding targeting a small fragment of the COI mitochondrial gene selected by PCR and sequenced using high-throughput next generation sequencing. The DNA metabarcoding results were compared with databases available online. These preliminary results validated a protocol based on commercial samples kept frozen (−20 °C) before analysis. Sequences allowed 34 different types of prey to be identified to the species level, including 17 teleost fish species. Results revealed the high occurrence of cuttlefish eaten by both species of squid. Food composition was analysed in order to make comparisons between species, between seasons (in L. vulgaris) and according to the size of the predator. Differences in diet of L. vulgaris between November and March samples were greater than the difference between L. vulgaris and L. forbesii, which is consistent with opportunistic behaviour in these squids. Differences in diet related to predator size do not suggest a change in trophic level during the growth of recruited stages.