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Scuba diver in reef

The Terminator

By David Stauth
News & Research Communications
Research in the Caribbean Sea and Atlantic Ocean

New research on the predatory nature of lionfish, the invasive species that is decimating native fish populations in parts of the Caribbean Sea and Atlantic Ocean, indicates that lionfish are not just a predator, but more like “The Terminator.”

Kurt Ingeman, a doctoral candidate in the Department of Integrative Biology within the College of Science, presented the findings this week at the annual meeting of the Ecological Society of America (ESA), the premier professional society of ecologists in the country. They were based on field experiments done with lionfish in the Bahamas, show further damage this species can do. The work was funded by the National Science Foundation and the Cape Eleuthera Institute of the Bahamas.

Most native predatory fish are attracted to prey when their numbers are high, successful attacks are easy and minimal energy is needed to catch and eat other fish, according to previous research by Michael Webster, a science alumnus who earned his Ph.D. in coral reef fish ecology. As the population of prey diminishes, native predators often go where the fishing is better.

In comparison, Lionfish appear to stay in one area even as the numbers of prey diminish and sometimes eat the population to local extinction, based on Ingeman’s new research. Lionfish have unique characteristics that make this possible. Like “The Terminator,” they simply will not stop until the last of their prey is dead.

“Lionfish seem to be the ultimate invader,” said Ingeman. “Almost every new thing we learn about them is some characteristic that makes them a more formidable predator. And it’s now clear they will hunt successfully even when only a few fish are present."

"This behavior is unusual and alarming.”

Ingeman conducted his research on replicated natural reefs in the Bahamas, measuring mortality of a particular prey species, the fairy basslet – a popular aquarium fish and a common prey of lionfish.

Predation rates were compared between reefs with the invasive lionfish and reefs with native predators alone, and across a range of population levels of the fairy basslet. It found that at a low population density of this prey fish, the rate of mortality with lionfish present was four times higher than that caused by native predators alone, such as medium-sized groupers or trumpet fish.

Fairy basslet
Fairy basslet, common prey of lionfish

Since fairy basslet live in small local populations, they are most vulnerable to local extinction. These findings are rather important, researchers say, because it reveals that the mechanisms that ordinarily regulate population size can be altered.

“Reef fish usually hide in rocks and crevices for protection, and with high populations, there is a scramble for shelter,” Ingeman said. “Native predators take advantage of this by primarily eating when the prey is abundant. As prey population levels decline, it takes a lot more energy to catch other fish, so they move on to other areas.”

Because of this process—scientists call it “density-dependent” predation—populations of native prey fish tend to shrink when they get too large, grow when they get too small, and are rarely ever wiped out completely.

Lionfish, however, have such advantages as an invasive species that they apparently feel no need to move on for better or easier hunting. They may not be recognized as a predator by other fish, leading to high mortality even when shelter is abundant. Lionfish are also very efficient hunters, can defend themselves well with their poisonous spines, and can thrive even at deeper levels in the ocean. They tolerate a wide range of habitats and conditions and reproduce rapidly most of the year.

Still unclear, Ingeman said, is whether evolutionary pressures may allow native fish in the Atlantic Ocean to adapt new behaviors that provide better defense against lionfish.

“Clearly there’s a strong pressure here for natural selection to come into play,” Ingeman said. “We know that fish can learn and change their behavior, sometimes over just a few generations. But we don’t have any studies yet to demonstrate this is taking place with native fish populations in the Atlantic.”

The lionfish invasion in the Atlantic Ocean began in the 1980s and now covers an area larger than the entire United States. With venomous spines, no natural predators to keep them under control and an aggressive behavior, lionfish have wiped out as much as 95% of the native fish in some hard-hit areas. These terminators will eat almost anything smaller than they are and can withstand starvation for long periods.

And many of their prey species may disappear before they do.