Predation plays a key role in determining marine community structure and dynamics. Due to their dietary flexibility, generalist predators are considered more successful than specialist feeders under ongoing climate change. Nevertheless, dietary specialization is often conceptualised as a fixed attribute derived from the fundamental niche, rather than as an ecological outcome reflecting resource use across spatial and temporal scales. The bearded fireworm Hermodice carunculata (Pallas, 1766) is an amphinomid polychaete that has emerged as a native invader in the Mediterranean Sea, rapidly expanding from central-eastern regions towards the western and northern sectors of the basin. Commonly classified as a generalist predator and scavenger, it feeds on fish carrion but also on a variety of living invertebrates, potentially threatening benthic keystone species. Given its ongoing expansion and Mediterranean ecosystems changes, understanding its trophic ecology is crucial.

Here, we investigated whether the bearded fireworm exhibits prey preferences under controlled conditions by evaluating its predation towards common Mediterranean prey previously reported in its field diet. After setting the optimal conditions in an experimental arena, ten prey pairings were tested. Predatory behaviour was recorded and analysed both qualitatively and quantitatively using tracking software.

The bearded fireworm consumed all prey, confirming its generalist feeding strategy, while showing prey selection, with fish as the most preferred one, followed by mussel (the lab diet), sea anemone and lastly jellyfish. Differences in predatory behaviour (e.g., certain/uncertain) and consumption times further supported this selection pattern, suggesting that, although the bearded fireworm exhibits a broad diet, its feeding behaviour may be influenced by nutritional or ecological requirements based on resource availability.

These results improve our understanding of the predatory pressure exerted by this species and highlight the importance of assessing dietary specialisation within generalist consumers to better predict their impacts on Mediterranean communities under the current climate change scenario.