Relevance of feeding ecology in the management of invasive species: prey variability in a novel invasive crab

Abstract

The diet composition of non-indigenous species (NIS) provides essential information to recognise potential impacts on ecosystems. This study examined the feeding ecology of the novel invasive crab Cronius ruber from demographic and seasonal perspectives. It identified 52 prey items in crab gut contents (n = 278), and more than 18% of the studied specimens had empty guts. The high-frequency prey belonged to Brachyuran (51.54%) and Polychaete (34.36%), followed by Echinidea (22.47%), Gastropoda (21.15%) and Perciformes (20.70%). Additionally, the night sampling showed prey that were not observed in the examined stomach contents. The daily ingestion rates based on polychaeta indicated more prey consumption by juveniles (<55 mm carapace width (CW)) and adults crabs (55 mm–75 mm CW) than the old adults (>75 mm CW). This falls in line with the number of prey items retained in individuals’ guts, which changed seasonally and in ontogenic groups. Moreover, the visual night observations showed that native predators foraged on the invasive crab. These predators were groupers, octopus and elasmobranchs. The seasonal and ontogenic differences observed in diet through the stomach content analysis and daily ingestion rates suggest that C. ruber eats a generalist diet. The dissimilarity analysis suggested possible resource partitioning in ontogenic groups. Our results could represent the baseline for future studies into the possible impacts of this invasive NIS, as well as some arguments to include C. ruber on the list of invasive alien species of European Union concern.