Biotic resistance on coral reefs? Direct and indirect effects of native predators and competitors on invasive lionfish

Biotic resistance is the ability of an ecological community to prevent or limit the establishment or success of non-indigenous species. Native species can confer resistance by outcompeting or directly consuming non-native invaders. The fear of being eaten could also limit invader success, but non-consumptive effects of native predators have rarely been documented as a source of biotic resistance. Here, we test whether native groupers on Caribbean coral reefs can promote biotic resistance to invasive Indo-Pacific lionfish through competition, consumption, and/or through non-consumptive effects. Stomach content analysis of more than 200 groupers, comprising five species, revealed no instances of predation on lionfish. To test for competitive and non-consumptive effects of groupers, we released tagged juvenile lionfish onto reef patches that varied in grouper densities and monitored lionfish behaviours over five weeks. At dawn, during peak grouper and lionfish hunting times, juvenile lionfish hid more on reefs with more grouper predators. Juvenile lionfish were also less active during the day on reefs with high grouper densities. Hiding and inactivity are incompatible with foraging and thus should result in lionfish eating fewer prey and having reduced somatic growth rates. Although there was no substantial effect of interspecific competition on lionfish behaviours, we found that lionfish swam greater distances with increasing densities of intraspecific competitors at dawn. We did not detect a cascading effect of grouper predators on smaller fishes, perhaps because the seasonal peak in prey fish recruitment masked the effects of lower lionfish predation. Fear of native predators by lionfish has the potential to reduce invader foraging success, although it might not fully mitigate the negative effects on native prey communities. Efforts to rebuild grouper populations throughout the Caribbean may still aid in controlling the lionfish invasion despite weak evidence of interspecific competition and lack of direct predation on lionfish, but further research is needed. At broader scales, our findings highlight that the global depletion of large predators can have implications beyond demographic effects on prey.

Automated summary

This study explores the biotic resistance of native groupers on Caribbean coral reefs to the invasive Indo-Pacific lionfish. While groupers did not prey on lionfish, their presence affected lionfish behaviors through competition and non-consumptive effects, leading to reduced activity and hiding among lionfish, resulting in lower foraging success and growth rates.