Invertebrate-dominated scavenging attracts insectivorous vertebrates following mass fish mortalities in a Mediterranean wetland

Mass mortality events create exceptionally large and unpredictable carrion resource pulses in ecosystems. While scavenger dynamics at individual carcasses has been relatively well documented, the functioning of scavenger assemblages at large carcass accumulations remains largely unexplored, despite the increasing frequency of these under global change. By monitoring 20 piles of common carp (Cyprinus carpio) carcasses (average 100 kg each) generated during mass mortality events in a Mediterranean wetland (between 2020-2024), this study provides the first joint characterization of vertebrate and invertebrate assemblages associated with large fish carrion pulses. We identified 35 vertebrate species and 20 invertebrate groups associated with carcass piles. Resource consumption was dominated by invertebrate assemblages, mainly Diptera and Dermestidae larvae, and this invertebrate dominance was reflected in the composition of carcass-associated vertebrate assemblages, which were largely composed of species feeding on the invertebrates present on the carcasses. Vertebrate use of carcasses followed a temporal pattern driven by changes in invertebrate availability during decomposition, resulting in a progressive turnover in vertebrate assemblage composition over time. Together, these results show that fish mass mortality events act as dynamic trophic hotspots in wetland ecosystems, where invertebrates play a central role in mediating energy transfer across the aquatic-terrestrial interface.