A secret snack: the diet of two key mesopelagic Antarctic fish species (Myctophidae: Electrona) is dominated by Arthropods and so far, overlooked gelatinous prey.

In the Southern Ocean, myctophids are the most successful pelagic fish group in terms of diversity, biomass, and abundance. They represent a major trophic link between primary consumers and megafauna, couple the surface and mesopelagic depths, and also represent an alternative trophic pathway in years where krill is scarce. Traditional stomach content analyses have often indicated that myctophids are major krill and copepods consumers, but have shown a bias towards soft-bodied organisms such as gelatinous zooplankton (GZP) and pteropods. In this study, we present a multimarker (COI and 18S) DNA metabarcoding analysis of the diets of two abundant myctophids in the Scotia Sea: Electrona antarctica and Electrona carlsbergi, with a particular focus on easily digestible taxa. Our findings reveal a diverse array of taxa in the diets of these species, primarily copepods and euphausiids, followed by pteropods and GZP. This comprehensive approach allowed us to test and confirm our hypothesis that GZP are common in the diets of both species. Specifically, salps and appendicularians are crucial components of the diet for E. carlsbergi, while hydrozoans play a secondary role in the diet of E. antarctica. Notably, E. carlsbergi consumed more appendicularians, chaetognaths, and hydrozoans during spring in the northern region of the Scotia Sea, while in autumn in the southern region, they prayed more on salps (predominantly Ilhea racovitzai) and other cnidarians. Our study contributes to a more nuanced understanding of the dietary habits of these pelagic fish species and the ecological dynamics of the Scotia Sea.