Non-linear effects of invasive lionfish density on native coral-reef fish communities

Abstract

One of the major goals of invasion biology is predicting the effects of invaders on native species, which is often accomplished by linearly scaling-up per-capita effects with invader abundance. However, the relationship between invader density and their ecological impact is poorly understood, and it is likely that the effects of invasive species scale non-linearly with increasing invader density. The Pacific red lionfish (Pterois volitans) is an invasive predator that has reached high abundances throughout the tropical and sub-tropical western Atlantic, Caribbean, and Gulf of Mexico. A single lionfish can have extremely large effects on native reef-fish communities, yet the relationship between lionfish density and their ecological effects is not well known. I manipulated juvenile lionfish densities on small patch reefs in the Bahamas and monitored the subsequent effects on native coral-reef fish abundance, biomass, richness, evenness, composite diversity, and community structure over 7 weeks. Native fish abundance and biomass decreased non-linearly with increasing lionfish density, with the largest drops in abundance and biomass at low lionfish densities and their effects leveling off at high densities. Lionfish density also significantly affected richness and community structure, but these effects could not be clearly classified as either linear or non-linear. Evenness and composite diversity were not significantly affected by lionfish density. Given that the effects of lionfish on native fish abundance and biomass level-off at high lionfish densities, it appears important to remove all lionfish from small patch reefs to have the biggest influence on conserving the native community.