Past, present, and future impacts of invasive Indo-Pacific lionfish on high-diversity Atlantic fish communities

Background/Question/Methods

Indo-Pacific red lionfish (Pterois volitans and P. miles) have rapidly invaded the Western Atlantic, Caribbean and Gulf of Mexico, producing a marine predator invasion of unparalleled speed and magnitude. Quantifying and mitigating the effects of predation by lionfish on invaded fish communities are now top priorities for conservation, but pose a major challenge because of the scale and complexity of lionfish-prey interactions in high-diversity marine habitats. To quantify the magnitude of lionfish predation impacts, and the extent to which lionfish populations need to be controlled to mitigate them, we develop a mechanistic model of lionfish-prey interactions on invaded habitats which draws on mass-balance and metabolic scaling principles. Our model accurately predicts observed declines in lionfish prey assemblages on nine invaded Bahamian coral reefs documented between 2008 and 2010.  Using our model and empirical data, we assess: (1) the cumulative amount by which lionfish have reduced the biomass of their fish prey, (2) whether populations of reef fish are currently in decline as a result of lionfish predation and (3) the extent to which lionfish density must be reduced to prevent further declines at the nine Bahamian sites.

Results/Conclusions

We estimate that lionfish have depleted fish biomass by 61- 95% across the reefs over a three year period, with the magnitude of decline largely driven by site-specific lionfish density.  Prey consumption by lionfish inhabiting continues to outstrip the production of their prey by an order of magnitude. Lionfish populations will likely continue to remove prey at rates far greater than reef fish populations can regenerate through somatic growth and reproduction across the system. Our projections for continued prey declines are robust to potential changes in both lionfish diet breadth and density-dependent prey production. To halt further erosion of native fish biomass, we estimate that lionfish densities must be reduced by 19- 93%. Rapidly increasing lionfish populations across the region are likely to have similarly severe effects on the biomass of native fish communities. However, management action, in the form of lionfish removal, may be effective in mitigating these effects at local scales if they maintain lionfish densities below levels which over-consume prey. Our model yields assemblage-specific targets for lionfish control that can be generated with local monitoring data, and are relevant to the scale at which ecological the ecological impacts and control of lionfish are occurring.