by Catherine MacDonald, RJD student
Anyone living in South Florida is familiar with the issue of invasive species—particularly the invasion of the Everglades by the African Rock Python (P. sebae) and the Indian Python (P. molurus) and the presence in the Florida Keys of large numbers of non-native Green or Common Iguanas (Iguana Iguana).
What you may not know, however, is that invasive marine species are also a big problem. Recent estimates by NOAA suggest that the total cost of invasive species to the U.S. economy is as much as $137 billion per year. Baltz (1991) provides a review of non-native marine fish introductions, reporting that well over 100 species have staged “invasions” worldwide, many as a result of ballast water releases in shipping, canal construction, or intentional transplantation for “fishery enhancement”. According to the U.S. Geological Survey’s Nonindigenous Aquatic Species Database, in the last 100 years more than 68 non-native species have been introduced just in Florida, the Caribbean, and the Gulf of Mexico. Once established, even intensive campaigns have failed to successfully eradicate invaders like the European Green Crab (Carcinus maenas) on the U.S. Pacific coast or a variety of ornamental fish including Siamese Fighting Fish (Betta Splendens) and the Yellow Tang (Zebrasoma flavescens) in the rivers and oceans of South Florida.
One of the most severe recent invasions has been staged by lionfish in waters of the Southeastern United States and the Caribbean. We have been invaded by two similar species: Pterois volitans, commonly known as the “red lionfish,” and Pterois miles, also known as the “common lionfish” or “devil firefish”. Both are from the family Scorpaenidae (related to scorpionfish and toadfish), and occupy similar ecological niches. However, they have distinct ranges: P. volitans is native to the Western and Central Pacific and the coast of Western Australia, while P. miles is found in the Red Sea, Persian Gulf, and Indian Ocean. Mitochondrial DNA analysis has demonstrated that the two species are genetically different. It is not known whether they are able to hybridize, although there are no known differences in their reproductive biology.
Approximately 93% of the lionfish population on the Easte
rn Seaboard of the United States is comprised of P. volitans. What is called a “founder effect” has occurred and these populations have low levels of genetic diversity. This tells us that most of these lionfish are descended from a relatively small number of ancestors. Limited genetic diversity is typical of invasive species in the early stages of introduction (Hamner et al. 2007; Freshwater et al. 2009).
Lionfish can grow as large as 17 inches (43 cm), live for more than ten years, and weigh up to 2.5 pounds at maturity. They are pair spawners and display complex courtship behavior before spawning. They are able to spawn throughout the year approximately once every four days, suggesting an annual fecundity of over 2 million eggs per female (Morris and Akins 2009). They remain in a larval stage for up to a month after hatching, and during this time can survive in ocean currents which allow them to distribute widely and rapidly. Research found no genetic difference between U.S. and Bahamian populations, and the introduction lag time (1980s in Florida, 2000 in North Carolina, 2004 in the Bahamas) and the history of larval connection between Florida and the Caribbean suggest an introduction location in South Florida.
Although some sources blame the 1992 release of six lionfish from an aquarium damaged by Hurricane Andrew into Biscayne Bay, records of previous sightings as early as 1985 make it clear that while those six may have contributed to the introduction of lionfish, they were not the vanguard. Genetic studies suggest that the founders of the current population originated in Indonesia, which exports a large proportion of the lionfish available in the aquarium trade, so the most likely explanation for lionfish introduction is release by aquarium owners after their fish outgrew available tanks (Hamner et al. 2007). It is also theoretically possible that larval lionfish could be carried in ballast water, although there is no conclusive evidence for this introduction vector.
Lionfish are thriving in both the warm temperate and subtropical regions of the Atlantic ocean, surviving year round as far north as southern Virginia. For an accurate idea of the scale of the problem, consider the following: one study observed an average lionfish density of 21 fish per hectare off the North Carolina coast in 2004. By 2007, mean densities were approximately 150 lionfish per hectare, with some sites showing more than 350 lionfish per hectare (Whitfield et al 2007). Similar densities are reported for the Bahamas (Green and Côté, 2009). These densities are orders of magnitude higher than those naturally occurring in the Pacific and Indian oceans.
The factors which control lionfish populations within their native ranges are unknown, as they appear to have few natural predators. Laboratory experiments have demonstrated that sea basses native to the Atlantic exhibit avoidance of lionfish as prey items (Morris 2009). Although there is evidence for grouper consuming lionfish in the Bahamas, how significant and widespread this predation might be is unknown (Maljković et al 2008). In any event, it is clearly insufficient to meaningfully limit lionfish population growth. In the Roatan Marine Park in Honduras, attempts are being made to “train” local shark populations to consume lionfish, on the theory that the strange fish (dissimilar to native species) is not being recognized as a potential food source by predators.
What’s the big deal?
There are many reasons that invasive lionfish are a problem. Lionfish are voracious eaters, and their diets include over 40 species of fish and crustaceans. They potentially threaten many of our native reef fish either through direct predation or by out-competing other piscivores for prey (Albins and Hixon 2008). Research suggests that shortly following lionfish introduction, survival rates for native fish decline as much as 80 percent. Through their aggressive feeding habits, lionfish may dramatically reduce survival of herbivorous fishes like parrotfish that help prevent seaweeds and macroalgae from overgrowing coral reefs. They are also fiercely territorial, limiting reef area available as habitat for other fish. Lionfish may even potentially perform niche takeovers of overfished predatory reef fish whose populations we are currently trying to rebuild.
Lionfish also eat the spawn of many commercially important fish, including yellowtail and vermillion snapper and the threatened Nassau grouper. In sufficient numbers, lionfish may interfere with beach tourism in the United States and the Caribbean because of their ability to inflict a painful venomous sting when threatened. Anecdotal reports suggest declines in their popularity and value as an aquarium fish subsequent to their establishment as an invasive species. While they were initially perceived as a dive attraction, declining numbers of native fish have led dive operators to become committed to trying to control lionfish populations.
There have been efforts to develop demand for a lionfish fishery, but their habits make capture labor intensive (usually involving spearing or hand netting) and their venomous spines and relatively small size limit their attractiveness as a fishery product. Moreover, establishment of a formal fishery would require that lionfish be regulated under the Magnuson-Stevens act, which would mandate managing their population for sustained long-term yields. There is no provision in the act for establishing a fishery intended to eradicate the species being fished.
What can you do?
- Report lionfish sightings! If you see a lionfish while swimming, diving or boating, you can report it at http://nas.er.usgs.gov/SightingReport.aspx. The more detailed data you can provide (including GPS coordinates or photos) the more useful your information is. You can also keep up with recent sightings by checking out the U.S. Geological Survey map of lionfish sightings, updated daily. It is available at http://nas.er.usgs.gov/taxgroup/fish/lionfishdistribution.aspx
- If you live in an area where lionfish populations are established, you may want to see if you can get involved in helping to reduce the number of lionfish in your area. There are many lionfish “derbies” in which teams compete to see who can bring in the largest number of the invasive critters. The non-profit organization REEF sponsors derbies and offers workshops in South Florida to educate divers about lionfish and best removal practices.
- Never, ever release any captive animal into the wild. It’s not kind to the animal or the environment. Contact local pet stores for help or post on Craigslist to find a new home.
- Write to your local or national representatives encouraging them to fund research and programs to study and try to eradicate lionfish, especially in vulnerable coral reef areas. Tell them we need to create aggressive action and response plans for addressing the problem of marine invasive species—so in the future we can act before populations become well-established. Don’t forget to mention your support for stronger legal protections for sharks and other marine life!
Baltz, D. (1991). Introduced fishes in marine systems and inland seas Biological Conservation, 56 (2), 151-177 DOI: 10.1016/0006-3207(91)90015-2
Wilson Freshwater, D., Hines, A., Parham, S., Wilbur, A., Sabaoun, M., Woodhead, J., Akins, L., Purdy, B., Whitfield, P., & Paris, C. (2009). Mitochondrial control region sequence analyses indicate dispersal from the US East Coast as the source of the invasive Indo-Pacific lionfish Pterois volitans in the Bahamas Marine Biology, 156 (6), 1213-1221 DOI: 10.1007/s00227-009-1163-8
Green, S., & Côté, I. (2008). Record densities of Indo-Pacific lionfish on Bahamian coral reefs Coral Reefs, 28 (1), 107-107 DOI: 10.1007/s00338-008-0446-8
Maljković, A., Leeuwen, T., & Cove, S. (2008). Predation on the invasive red lionfish, Pterois volitans (Pisces: Scorpaenidae), by native groupers in the Bahamas Coral Reefs, 27 (3), 501-501 DOI: 10.1007/s00338-008-0372-9
Morris, J., & Akins, J. (2009). Feeding ecology of invasive lionfish (Pterois volitans) in the Bahamian archipelago Environmental Biology of Fishes, 86 (3), 389-398 DOI: 10.1007/s10641-009-9538-8
Whitfield, P., Hare, J., David, A., Harter, S., Muñoz, R., & Addison, C. (2006). Abundance estimates of the Indo-Pacific lionfish Pterois volitans/miles complex in the Western North Atlantic Biological Invasions, 9 (1), 53-64 DOI: 10.1007/s10530-006-9005-9