Over the course of human existence various species have been accidentally and intentionally introduced into new environments. This can often lead to serious environmental consequences. The invasive species often push native species into extinction creating an imbalance in dynamics of the ecosystem. Kudzu, the Emerald Ash Borer, and lionfish are all examples of species that were intentionally or accidentally introduced into the United States. Each of these species has created an ecological nightmare for the various ecosystems that they inhabit.
The lionfish (Pterois volitans) is a top level predator among the coral reefs and rocky shores of the Indo-Pacific. Their natural range extends from Australia and Malaysia in the west to French Polynesia in the east. Their north to south distribution extends from Japan to New Zealand. Lionfish can be found across a wide range of marine habitats ranging from hard bottoms, mangroves, and sea grass beds to coral reefs and artificial habitats like shipwrecks. They can also be found in as little as 1 foot of water and as deep as 1000 feet. The juveniles tend to be found in the shallower areas while adults reside in the deeper regions.
Lionfish were first reported in the Atlantic as early as 1985. By the early 2000s it was confirmed that they had established an Atlantic population. Their Atlantic / Caribbean range extends from New York to Bermuda with populations spreading towards South America. Belize reported their first lionfish sightings in 2008 along the norther reaches of their barrier reef. Within less than a year lionfish sightings were reported across the entire length of the Belizean barrier reef. In some regions of their invasive range the lionfish density has been reported as high as 1,000 individuals per acre. In some instances their density has surpassed that of various native species of fish.
Growth of the LionFish Population in Belize
In 1985, when lionfish (Pterois volitans) were first introduced into the Atlantic, their population size was estimated to be between 8 – 12 individuals. Since then their population has gone through exponential growth enabling them to spread uncontrollably across their new range. Females have a biotic potential of producing 2 million eggs per year and reproducing every four days. Biotic potential is when an organism produces the maximum number of offspring possible during each reproductive event. An abundance of resources and the lack or reduction of limiting factors that would control population growth made it easier for the lionfish to achieve their biotic potential. Limiting factors are forces present in every community that prevent individuals from achieving their biotic potential. Forces like predators, disease, and competition for food and space are examples of limiting factors. If the limiting factors are too oppressive, populations tend to decrease while if limiting factors are reduced or removed, the population size tends to increase. With no Caribbean based predators and all of their other limiting factors being nonexistent, the Belizean lionfish population is on a path to explode across the entire length of the Belizean barrier reef.
Native fish communities along the entire length of the Belizean barrier reef have been severely impacted by the spread of this invasive predator. Lionfish occupy the same trophic level as snappers and groups but they do not have any natural predators in the Atlantic and Caribbean ecosystems. This lack of predation, along with a massive reproductive potential is what is allowing the lionfish population to grow with little to no regulation.
Organizations like the National Centers for Coastal Ocean Science, U.S. Geological Survey, and a multitude of local Belizean agencies have been monitoring and working on management strategies to deal with the Belizean lionfish problem. Much of the monitoring has been done by volunteer groups during recreational diving as well as lionfish hunting tournaments. In many regions there are no restrictions on the number of lionfish that can be collected by spearfishing, netting or line fishing. During a collection dive lionfish of every size are harvested. Once on shore the stomach contents of the lionfish are examined to determine the prey species that they have been feeding upon. The data collected from a decade of monitoring has helped marine biologists recognize the severity of the lionfish invasion.
Lionfish Impact in Belize
The introduction of lionfish into the Atlantic and Caribbean is one of the many factors that has helped contribute to the disruption of the coral reef communities along the eastern coast of the United States and the Caribbean, including the Belize barrier reef. Invasive lionfish have shown to prey upon twenty-one different families of small reef fishes as well as numerous different species of crustaceans. Their feeding preferences, along the coast of Belize and the rest of the Caribbean, have caused them to be in direct competition for food with snappers and groupers. Juvenile lionfish tend to feed mainly on crustaceans while the adults prey almost exclusively on fish.
Lionfish have shown to exhibit a higher consumption rate when compared to similar sized native predators. They have been recorded to have 2.4 times the negative impact upon reef fish populations compared to the native predators in the same environment. One study conducted in the Bahamas discovered that lionfish reduced the prey fish population by 90% over the course of two months compared to a 35% reduction of reef fish populations by the native coney grouper. A significant concern is that if invasive lionfish continue to deplete their preferred prey base they will eventually turn towards consuming juveniles of economically important species. The loss of the preferred prey base will also produce a ripple effect through the coral reef ecosystem since most of the prey species are herbivores that help control the growth of algae on the reef. Removal of these herbivores leads to an increase in algal growth which eventually leads to a decrease in the survival rate of corals. These negative impacts, along with a variety of other factors, are contributing to a decline in the stability of the coral reef ecosystems throughout the Atlantic and Caribbean.
Dave Cox is a Professor of Biology, author, and President of Howler Publications. He has been leading study abroad trips to Belize, for students and community members, to study tropical ecology, marine biology and Mayan culture since 2007. If you would like to join Professor Cox on a lionfish hunt in Belize contact him at [email protected] for more details.
Image sources:
- map: NOAA Ocean Services
- all photos courtesy of VivaBelize and used here by permission
