Using molecular and stable isotope markers to identify the main predators of Nephrops norvegicus in Mediterranean deep-water ecosystems

To obtain a better understanding of the functioning of ecosystems and how they respond to disturbance, it is necessary to identify the relevant biotic interactions and specific trophic roles. Predation is one of the most important biotic interactions that can also define the spatial patterns of other species. Many predators are considered key species for the functioning and maintenance of ecosystems, as they play an important ecological role that can influence the dynamics at lower trophic levels. The Norway lobster Nephrops norvegicus is one of the most valued European fishing stocks. However, its value and capture have declined over the last decade. In the Atlantic Ocean, Atlantic cod Gadus morhua is the main predator of N. norvegicus . However, this species is not present in the Mediterranean Sea, and little is known about which species might prey on N. norvegicus in this area. Here, we combine 2 methodologies—genetic identification of stomach contents and stable isotope analyses—to identify, for the first time, the main predators of N. norvegicus in the Mediterranean Sea. Moreover, we have created the Predation Index, which determines the most influential predator affecting N. norvegicus population dynamics. Our results reveal that the major predators are the cephalopods Sepietta spp. and Abralia veranyi , which probably affect the early stages of N. norvegicus , followed by the elasmobranch Scyliorhinus canicula and the bony fishes Merluccius merluccius , Trigla lyra , and Conger conger . To evaluate possible fluctuations in the N. norvegicus population, we consider the assessment of these predator populations crucial.