Opportunistic feeding by a flatfish mesopredator across spatially distinct benthic assemblages— an integrative DNA metabarcoding approach

Soft-sediment habitats support diverse benthic communities and demersal fish populations, but are facing growing anthropogenic pressures, leading to shifts in predator-prey dynamics. For example, populations of small predators such as the oceanic Lusitanian solenette Buglossidium luteum have rapidly increased, with potential impacts on the benthic food web. Stomach content analyses offer a direct way to uncover trophic relationships, but traditional morphological methods can lead to under-representation of certain taxa and an under-estimation of the diet range of small predatory flatfish. Here, we utilized an integrative approach, combining DNA metabarcoding and morphological identification of solenette gut contents collected in the south-eastern North Sea. These observations were further correlated with benthic infauna data of the respective sampling stations. The diet of solenette in the south-eastern North Sea was characterized by a high diversity with a total of 164 different taxa with a clear emphasis on crustaceans and polychaetes across all benthic assemblages in the studied area. However, there was a strong spatial differentiation in prey composition, highlighting solenette as highly opportunistic benthic feeders. DNA metabarcoding detected more prey taxa than morphology alone, highlighting its superior resolution and ability to reveal hidden diet components. The displayed flexibility in the diet of solenette likely contributes to the ongoing success of this flatfish in northern European seas. Consequently, along with warming sea temperatures and the mesopredator release caused by decades of fishing activities, this small benthic predator may exert considerable predation pressure on benthic infaunal communities of the North Sea, with so far unpredictable implications.