Messy eaters and scavenger hunts: the community ecology of scavenging interactions in a rockpool ecosystem

Abstract

Carcasses are valuable resources to those scavengers able to access them. While some generalist foragers are poorly equipped to process carcasses themselves, they may exploit the actions of others by feeding on tissues that the latter expose or detach. Carcasses also attract opportunistic predators, which can target other smaller scavengers, as well as feeding on the carcass itself. We studied these interactions using field-based experiments in a rockpool ecosystem. First, we showed that greater numbers of small fishes and mysids were attracted to areas where scavengers, primarily hermit crabs (Pagurus bernhardus), were feeding on mussel carcass baits compared to treatments where inaccessible carcasses or no-carcass controls were presented. We termed these secondary scavengers, since we did not see them feeding on the carcass directly. Second, we saw predators attack scavengers more frequently in trials where carcasses were present than where they were absent. They also approached stimulus chambers containing aggregations of hermit crabs more often than empty controls. Nonetheless, predator interactions were, overall, infrequent. For these smaller scavengers, carcass-foraging may be a trade-off between access to a sizeable food resource and competition, and sometimes heightened predation risk, from larger scavengers.