Hannah Armstrong, RJD Intern
Invasive species have the potential to negatively effect normal ecological function in any environment. Marine biological invasions are increasingly common, most notably that of the Pacific red lionfish (Pterois volitans). While the lionfish invasion and its direct effects on native fish communities has been well researched, there has been little documented evidence regarding non-predatory interactions. In a 2014 study by Raymond, Albins and Pusack, they observed whether Pacific red lionfish and Nassau grouper, two species that occupy similar habitats, compete for shelter and whether or not the competition is size-dependent.
Pacific red lionfish (Pterois volitans) have been reported in the Atlantic Ocean since the mid-1980s and now pose a threat to the western Atlantic and Caribbean coral reef systems. As small-bodied predators, they are capable of significantly reducing the abundance and diversity of native fishes via predation. Nassau groupers (Epinephelus striatus), despite being regionally endangered, are a larger predator found throughout the lionfish’s invasive range. Because these two species use similar resources and compete for similar habitats, it is important to understand how they interact and what may result from their competition.
In order to investigate how Pacific red lionfish and Nassau grouper affect each other’s behavior, the three scientists set up an experiment to compare their distance from and use of shelter when in isolation versus when both species were in the presence of each other with limited shelter. The two species were first held in separate cages with partitions to allow for isolation periods lasting 24 hours, and interaction periods lasting 48 hours, with each cage containing a shelter that the scientists constructed. The trials were based on size-ratio treatments: first they observed similarly sized lionfish and Nassau grouper, then they observed a juvenile lionfish and a substantially larger juvenile Nassau grouper, and lastly they observed an adult lionfish and a much smaller juvenile grouper. Finally, to test for predation between the two species, they incorporated a prey fish in some of the trials.
Upon statistical analyses, Raymond, Albins and Pusack eventually came to two conclusions regarding the interactions between these two species, and specifically Nassau grouper avoidance behavior: first, they found that when Nassau grouper interacted with smaller lionfish, they avoided them by moving further from the shelter occupied by lionfish, and by using the shelter less often, and second, they found that when Nassau grouper interacted with similarly sized lionfish, they avoided them by increasing their proportion of shelter use, and by avoiding the part of the experimental cage where lionfish were consistently present. The scientists ultimately found that the Nassau grouper significantly changed position relative to shelter in the presence of lionfish, however the lionfish did not change their positioning upon interacting with the Nassau grouper. This demonstrates how they have a tendency to compete for limited shelter, and the manner in which the Nassau grouper avoid lionfish is size-dependent.
While this study highlights the competitive interactions for shelter between invasive Pacific red lionfish and Nassau grouper, it is important to note that it was performed in a laboratory setting. For future conservation efforts, it will be critical to consider how this might apply in a natural reef habitat, and whether or not this competition could lead to lionfish being a dominant predator rather than the native Nassau grouper, a shift that may result in trophic cascades.
Raymond, WW, Albins MA, Pusack TJ. Competitive interactions for shelter between invasive Pacific red lionfish and native Nassau grouper. Environ Biol Fish (2015) 98:57-65. 31 January 2014.