Here's a research essay I wrote on the little buggers (it really long, about 2300 words)
Beauty with a Sting
Human culture, namely American culture, has long thought of itself as a god, able to experiment and manipulate anything in our world, purely for our entertainment. We see no harm in doing so, because we are sure of our abilities to control the world. But what if our actions unleashed an unrelenting killing machine, right in our home waters? And what would happen if we couldn’t find a way to stop it? Unfortunately, biologists and ecologists of the Caribbean and Western Atlantic are facing these questions right now, as the persistent march Indo-Pacific Lionfish Pterois volitans and Pterois miles is wreaking havoc across the various coral reef systems of the WA. Several ideas have been brought up to find ways to stop the invasion of Lionfish, such as utilizing natural bio-controls (which is simply training/influencing a current native species to target invasive Lionfish) or targeted removals. Although the advancement of invasive Indo-Pacific Lionfish (namely Pterois volitans) through the Caribbean and Western Atlantic is happening at a staggering rate, carefully implemented steps like targeted removals done consistently in high risk areas can possibly put an end to this species destruction of reef ecosystems.
But to properly understand why this invader is so destructive, one must first look into its natural biology, and what makes it an effective hunter. Lionfish are, as a general rule, ambush predators. But they stand out from other types of ambush predators because they do not make any effort to camouflage or conceal themselves. In contrast, they actually stand out from their surrounding almost completely. So why are they such effective predators, even though they hide in plain sight? Biologist Oona M. Lönnstedt theorizes that P. volitans has “evolved to avoid prey detecting its presence, and to prohibit “anti-predator†response (referring to any evasive or defensive course of action) in prey fishes (Lönnstedt)â€. Lönnstedt has performed many experiments on popular prey items such as damselfish to see how they respond to certain cues linked to predators, such as visual and scent-related stimuli. Her experiments were centered on a prey damselfish, Chromis viridis, and how it responded to stimuli from the Rock Cod, a common predator of the WA, the Zebra Lionfish (Dendrochirus zebra), a relative of the Red Lionfish and another predator native to the WA, and P. volitans, otherwise known as the Red Lionfish and the fish this study is targeting. (Lönnstedt, Figure 4)
The study exposed test C. virdis to fake and real stimuli related to each species, to find out if it could take the necessary anti-predator responses to survive, and in an effort to “train†the prey fish. Then the scientists put the prey fish in actual tanks with each predator, to see if their learned behaviors could kick in and let them survive. As the graph indicates, survival rates were high among the fish exposed to the real olfactory cues of C. microprion, whereas the fish exposed to the fake stimuli had a much lower survival rate. The same can be said about the fish tested the D. zebra. But remarkably, the fish conditioned to the real and fake stimuli of P. volitans did not survive at all, and all of the test subjects were hunted down in less than a day. This study alone illustrates how deadly and incredibly efficient P. volitans is, as well as it amazing ability to pass unnoticed by prey items. But how did this deadly predator show up in an ocean on the other side of the planet? For that answer, one must look to Biologist Ricardo Betancur. In his article “Reconstructing the Lionfish Invasion: Insights into the Greater Caribbean biogeographyâ€, he explains how quickly lionfish have spread, and why. Betncur states that lionfish are a popular in the aquarium trade because they make great show pieces, and that they were likely introduced into WA waters because owners decided that they did not want to keep their specimens any more, but did not want to kill them either. He also shares that there are documented accounts of Lionfish escaping aquariums when hurricanes hit Florida, the best documented case of this being a report after hurricane Andrew. From there, the lionfish population exploded, quickly expanding all the way to North Carolina, throughout the Caribbean and across the northern coast of South America, all in 10 years from their first original sighting from SE Florida (Betancur). Another factor in their population explosion is that lionfish spawn year round, laying egg masses that float along the currents of the sea, dispersing the eggs across vast areas very quickly. So the question is, how do we get rid of them now that they are established?
For the answer to that question, we must first look to Andrew B. Barbour, and his article “Evaluating the Potential Efficacy of Invasive Lionfish Removalsâ€, which appeared in the academic journal Plos One. Through many different studies done by Barbour and his colleagues, he has come to the conclusion that not only is lionfish control/eradication unlikely, but also unwise without further study into how they interact with coral reef systems. “Furthermore, such a lionfish fishery would be limited to shallow water (≤30 m) spearfishing and handnetting as lionfish have a low vulnerability to capture by hook and line. This gear and depth limitation provides potential refugia from fishing, potentially making removal efforts less effective (Barbour).†To further explain Barbour’s statement, lionfish can be found in water hundreds of feet deep, thereby greatly limiting the amount of possible hunting ground, and giving the lionfish a large amount of area to take refuge in. Barbour also explains that removal of larger adults can cause a much larger population of smaller individuals that could feed on the young of other species more readily than the adults, which will drastically reduce the amount of individuals of prey species that survive to adulthood (Barbour). To put it simply, larger numbers of smaller individuals in the place of smaller numbers of larger individuals would cause much more long term impact because the larger number of smaller individual would predate highly on other young fish, drastically reducing the amount of fish that actually make it into adulthood to reproduce and create new generations of fish. Although this information should definitely be taken into consideration, there is another side to this argument, one that utilizes data instead of theory.
The other side of this argument can be found in the hands of Jesús Enesto Arias-González. He used a widely known and used an advanced simulator called Ecopath with Ecosim to predict the impact of lionfish removals under various situations and conditions. González used four main scenarios. The first had heavy fishing pressure with a high death rate on adult lionfish for five years then the fishing stopped. The second scenario applied a continuous but lower fishing pressure on the adult lionfish. The third and fourth mirrored the first two, only the selected targets were the middle-aged lionfish.
(González)
The results of the tests were surprising when heavy fishing pressure was applied, populations of lionfish were drastically reduced. But once the fishing stopped, the lionfish were able to bounce back fairly quickly. On the other hand, when continuous pressure was applied, same decrease in population was seen, but the lionfish were not able to rebound as before because of the continual removal of individuals. The data González provides is a very clear indicator that lionfish can in fact be removed by unnatural methods, but the pressure has to be kept up for long periods of time for the removals to be effective. One incentive that is quickly becoming popular among those who already hunt down this invasive species is the discovery that lionfish are very tasty, and are becoming a favorite to people who live on the coast. The fact that they are also readily available means that they can be hunted without worry of disturbing the ecosystem, or their populations.
Another possible insight on how to control lionfish populations is their apparent site fidelity, or preference of staying in a certain area. This data has been brought to light by biologist Zachary R. Jud. As he explains in his article “Site fidelity and Movement Patterns of Invasive Lionfish Pterois Spp., in a Florida Estuaryâ€, lionfish, especially young lionfish, have a very high tendency to stay in an area that they grew up in, instead of migrating to new areas as they get older. “Lionfish in the Loxahatchee estuary appear to exhibit extremely high site fidelity over extended periods of time and across multiple size classes. We found that a large percentage of tagged individuals were recaptured at the same location (often within a few cm) as their previous capture, even after weeks or months at liberty (Jud).†Simply put, individual lionfish like to stay in one general area, not bothering to change locations due to factors like predation from larger predators or competition for food. The only known reason as to why/how lionfish appear in new areas is that their eggs float along ocean currents, enabling them to travel to new areas fairly easily. The fact that mature individuals do not migrate to new areas gives researchers and conservationists’ alike hope because when fish culls are done in areas with lionfish, they do not have to worry about adults from other areas coming in to replenish the population. Once the population of an area is under control from human intervention, the people of that area only have to worry about keeping the juvenile populations down.
The next possible way to control lionfish populations is a method that would greatly contribute to lionfish removal efforts, and this method is called bio-control. This method utilizes the natural predators already present in the reefs, and “trains†them to go after lionfish as a new food source. There are conflicting opinions on how effective this method would be, even if it proves to be possible. Referring back to Barbour, he believes that natural predation on lionfish by other predators is unlikely, as he says in his article discussing different removal methods. “Furthermore, known instances of predation upon lionfish in the Western Atlantic are rare and limited to incidental natural occurrences of predation by such species as groupers and green moray eels, Gymnothorax funebris. Moreover, predation on juvenile lionfish by common reef predatory species in laboratory trials suggests low predation vulnerability (Barbour).†Barbour is saying that predation on lionfish from the natural predators present in/on the reef is something that occurs very little in invaded areas or in a controllable lab setting. But Barbour does not specify his evidence on what lab trials were conducted to verify this reasoning, so one can only assume that the experiments were done thoroughly. However, biologist Peter J. Mumby offers a different opinion, one that is based on occurrences from an actual reef ecosystem. In his article “Grouper as a Natural Biocontrol for Invasive Lionfishâ€, Mumby describes a reef, Exuma Cays Land and Sea Park, which has a strict fishing ban in place that has high levels of large-bodied groupers present because they are not being fished out. This has turned into a major benefit for ECLSP because lionfish did not even become established in the area until 2007, much later than areas surrounding it (Mumby). Mumby believes that the high volume of large bodied groupers have been keeping the lionfish at bay, and consuming any up to that point before they could establish a population. And even though the lionfish are established in that area now, the explosive population spikes have not been seen, most likely because the groupers have begun to utilize the lionfish as a main food source, and thereby keeping their populations in check. Other evidence offered by Serena Hackerott reveals this instance to be questionable. In extensive studies across much of the Caribbean, Hackerott was unable to find much, if any, correlation between to total abundance of natural predators and the numbers of lionfish present as well. “We did not detect a significant relationship between lionfish density and any metrics of native predator abundance, which included both aggregative measures of abundance (i.e., biomass and density) of total predators, large predators, small predators or total grouper (Hackerott).†Simply put, there is no definitive data that shows any correlation between the presence of natural predators and lionfish populations. This study, which was much more thorough and expansive than Mumby’s, gives a better illustration of how natural predators interact with invasive lionfish. This news is rather disheartening, as it eliminates a possible way of stopping invasive lionfish from spreading.
To come to a conclusion, all of the biologists currently working on ways to control this invasion unanimously agree that total eradication is only a dream, and that the best they can hope for is to stop the rapid advancement of invasive lionfish with the simplest solution, which is targeted removals of lionfish via community efforts in affected areas consistently done for the foreseeable future. Luckily, the lionfish’s apparent site fidelity will provide a slight relief for conservationists, as they will not need to worry about adult populations migrating into controlled and stable areas. Unfortunately, there is no definitive data that suggests biocontrol measures will be effective, therefore creating an even greater need for community efforts to fill in the gap of natural predation. And an added bonus to targeted culling’s of lionfish is a very large amount of free food! So the answer is clear, only human intervention can solve the problem that humans are responsible for in the first place.