Twelve to fourteen inches long. Eighteen venomous spines. Gaping mouth that devours prey 40% of its body length.
If you think this sounds like the start of a horror movie, you’re partially right. The monster in question is a lionfish (Pterois volitans and P. miles). A carnivorous fish native to the South Pacific and Indian Oceans, the lionfish is a prime example of an invasive species. It’s taking over reefs from South America to the Caribbean at an alarming rate. NOAA ecologist James Morris dubbed lionfish “one of the greatest threats of this century to temperate and tropical Atlantic and Caribbean reefs.”
Considering the other catastrophes facing our oceans—climate change, acidification, and human development, to name few—this is saying something. The invasion pattern, impact, and management strategies of the lionfish problem offer a powerful case study of what happens when a species shows up where it doesn’t belong, and what—if anything—we can do to stop it.
The history of the lionfish invasion has almost comical origins. In 1992, during flooding caused by Hurricane Andrew, six lionfish escaped from an exotic species attraction at a Florida aquarium. The fish hopped into the Gulf of Mexico, began to reproduce, and quickly spread through the Western Atlantic, Caribbean, and The Bahamas. Today, the species can be found as far North as New York, as far South as Venezuela, and as far West as Louisiana. The scale and speed of the invasion is alarming. In their native range, about 80 lionfish live in a cubic acre. In the Bahamas, about 400 lionfish per acre dominate reefs.
In addition to their quick spread, several other key factors ensure that when lionfish arrive in a habitat, they make their mark and stay. First, lionfish are fierce predators of native reef fish. In the Caribbean, they feed on ecologically and economically valuable species like Nassau and Warsaw groupers. They capture these prey using venomous spines: eighteen mane-like spokes containing acetylcholine and neurotoxins, which immobilize the victims through swelling and paralysis. Second, lionfish can invade virtually any type of habitat. They settle in water from just below the surface to 300 meters deep, in habitats from coral reefs to seagrass beds to mangroves.
More alarming than predation or habitat range, though, is a third characteristic: lionfish have no known predators in their range of invasion. Although sharks, groupers, and large eels prey on lionfish in their native Indo-Pacific, not a single species has been seen eating lionfish in tropical coral reefs. What happens when you have a fast-spreading species with formidable predation, versatile habitat choice, and no form of natural population control? Disaster. NOAA scientists call lionfish “the most significant change in biodiversity and community structure of reef fish since the beginning of industrialized fishing.”
In addition to the immediate threats of predation and habitat use, the long-term consequences of lionfish invasion are even more severe. Lionfish devour both top-level predators, like bass and grouper, and algae-eating herbivores, like parrotfish and surgeonfish. This leads to cascading disruption of the entire food web of a reef. Because many of these species are already threatened, lionfish pose a direct threat to biodiversity.
The consequences of the invasion also extend beyond natural ecosystems to human communities. The Bahamas, for example, relies on fishing and tourism for economic stability. These industries are less viable when all the popular reef fish are going extinct—or when a tourist’s snorkeling trip can end face-to-face with eighteen purple venomous spines.
The threats posed by lionfish to humans and ecosystems are myriad, complex, and severe. So what are we doing to fix the problem?
First, it’s worth asking whether the lionfish problem has the potential to fix itself. Studies of invasive species dynamics suggest that most invaders eventually reach a population ceiling. The arrival of a species follows the pattern of a population growth curve: a lag phase as the species enters the environment, an exponential growth phase as it rapidly increases in number, and a transitional phase as the species begins to level off. Eventually, the species reaches the limits of the environment—predation, parasitism and disease, or competition for resources—and begins to die off. Ideally, this same principle will apply to lionfish; they’ll eventually be eaten, die off, or outcompete themselves.
Unfortunately, the clues don’t point to this lucky outcome. Lionfish are missing some of the key limiting factors: they don’t have known predators or parasites and they don’t appear to compete with each other even at high densities. More importantly, we can’t afford to wait around to see when and if they’ll hit a ceiling. Certainly, lionfish will decline eventually—but will this happen only after they’ve eaten nearly every single native fish in the coral reefs?
The problem of lionfish invasion, like many other environmental threats, calls for a proactive and creative response. Scientists are hard at work finding strategies to prevent lionfish from invading new habitats and to control populations where they already exist. For example, studies have looked at altering reef patches to make them unattractive for settlement of lionfish larvae. Others have considered introducing native predators from the Indo-Pacific to the zone of invasion, but biological control comes with its own set of risks.
The most effective efforts take a far simpler approach: find the lionfish, catch them, and take them out. Throughout the tropics, a key form of lionfish mitigation is removal of the fish one by one. Studies have shown that a minimum of 35% to 65% of total lionfish need to be captured to make a dent in the population. Governments and environmental agencies therefore enlist the help of local residents and provide incentive for lionfish capture. In the Florida Keys, lionfish hunting has economic rewards. Tournaments and derbies recruit lionfish hunters with signs: “Wanted: Lionfish, Dead or Alive!”. Local stores provide discounts for the rental of scuba gear in exchange for captured lionfish. Some universities even offer community service credit for students who remove lionfish.
Such management is not likely to make a dent in the hundreds of thousands of lionfish in the oceans. However, local control buys time for the possibility of new technology and scientific developments to aid in larger-scale techniques for control.
In the Bahamas, where a fishing and tourism-based economy increases the nation’s vulnerability to the invasion, lionfish management exists on a whole new level. The country is currently facing decline in native species like conch and grouper, which are commonly overfished because of their popularity as a food.
The threat of overharvest to these species could be augmented by predation from lionfish, but instead the country has come up with an innovative solution: the Bahamas has begun to market lionfish as an alternate source of edible fish. Market booths sell lionfish (poisonous spines removed) alongside traditional dishes of fried conch. Restaurants serve it as an exotic luxury. The Bahamas have turned an ecological problem into an economic resource, with the side benefit of protecting biodiversity.
Lionfish derbies, restaurant specials, and scuba dive capture raids run the risk of making the lionfish problem seem whimsical and light-hearted. However, between the lines is a powerful message about the stability of our ecosystems and our responsibility to maintain them.
Lionfish in and of themselves are alarming—one look at their poisonous purple mane is enough to send anyone out of the water. More significant, however, is the potential of lionfish to interact with other habitat stressors—bleaching, climate change, acidification, overfishing, and pollution. At a time when increased anthropogenic threats call for the most resiliency and stability, lionfish are decreasing the capacity of marine environments to respond to change.
The moral of the lionfish story is two-fold. On the one hand, there is no easy solution. Such a complex and wide-reaching threat requires response on the part of multiple stakeholders, from local governments to environmental groups to scientists to snorkelers. The second moral, thankfully, is much more straight-forward: if you own exotic purple-spiked poisonous fish, don’t let your pets escape.
Emily Boring is a sophomore in Pierson College. Contact her at firstname.lastname@example.org.
(Featured images from Creative Commons.)
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