Innate feeding plasticity and animal prey support invasiveness of aquatic species in a southwestern European estuary

Non-indigenous species often rely on trophic plasticity to adjust to available food sources and even to avoid interspecific competition while overcoming environmental constraints during the establishment phase and, eventually, as they become invasive. The Atlantic blue crab Callinectes sapidus Rathbun, 1896 is expanding quickly in southwestern Europe and northwestern Africa, raising concerns about its impacts. Its feeding ecology in non-native areas is poorly understood, so this study aimed to 1) unveil the diet and feeding strategy used by the Atlantic blue crab in a highly invaded European estuary, 2) evaluate if their invasiveness was facilitated by an invasion meltdown process concerning trophic facilitation, and 3) determine its trophic position. Metagenomic analyses of gut content and stable isotopes showed that the species relied on opportunistic and carnivorous feeding traits and preyed mainly on native animal species, such as fish, shrimps, and oysters. We did not observe evidence of a widespread invasion meltdown process through trophic facilitation mediated by other invaders. The Atlantic blue crab’s trophic niche overlapped with two native crab species, particularly the European green crab Carcinus maenas (Linnaeus, 1758), while it’s high trophic position (4.3 ± 0.5) reflected the reliance on animal prey. These evidence suggests that trophic plasticity likely contributed to the invasiveness of the Atlantic blue crab because of its ability to exploit readily available prey. The Atlantic blue crab metapopulation is expanding and increasing over a vast region, and unfortunately a series of cascading effects throughout the food web can still be expected, as observed elsewhere.