A coral-reef fish alters recruitment in response to native but not invasive predator

Background/Question/Methods

Predators have a large influence on prey survival, so it is advantageous for prey to recognize and appropriately respond to predator cues.  Yet when a non-native predator is introduced into a system, prey may not recognize the novel predator’s cues, which can cause high prey mortality rates and contribute to the success of the invader.  Most coral-reef fishes undergo a transition from pelagic larvae to benthic juveniles (‘recruitment’), during which some species avoid visual and chemical cues from predators.  However, whether coral-reef fish alter their recruitment patterns in response to invasive predators is unknown.  To test the hypothesis that new recruits of native coral-reef fishes avoid reefs with native predators but not reefs with invasive predators, we constructed standardized habitat patches and randomly assigned one treatment to each patch: caged invasive predator (lionfish, Pterois volitans), caged native predator (graysby, Cephalopholis cruentata), or one of three controls.  A pair of divers returned to the reefs each morning for approximately two weeks to count and remove all new recruits and to rotate treatments among patches.  We then altered the diet of caged predators and repeated the experiment to test whether new recruits respond to the diets of predators or to other cues.

Results/Conclusions

Bicolor damselfish (Stegastes partitus) and mahogany snapper (Lutjanus mahagoni) had the highest recruitment to standardized habitat patches, with over 1200 and 780 total new recruits, respectively.  During the first experiment, there were significantly fewer mahogany snapper recruits on patches with the native predator compared to empty cage and empty patch controls, and a trend towards lower recruitment compared to invasive predator patches.  During the second experiment, there were significantly fewer snapper recruits to native predator patches than to invasive predator and empty cage control patches regardless of predator diet.  Overall, there was a greater than 50% reduction in snapper recruitment to patches with the native predator compared to invasive predator and control patches. There was no significant effect of treatment on bicolor damselfish recruitment in either experiment.  These results suggest that recruits of at least one commercially important coral-reef fish may not recognize or avoid the cues of an invasive predator compared to a native predator.  Furthermore, the effects of invasive lionfish on local densities of some coral-reef fishes are likely even greater than previously thought because prior studies documenting the effects of lionfish predation have assumed equal recruitment to reefs with lionfish compared to reefs with native predators.