College Station (Bernd F. Laeschke – December 2011): More than 40 non-indigenous species are spreading through the Gulf of Mexico, including lionfish and tiger shrimp. Pterois volitans and Pterois miles, known collectively as the lionfish, have been a growing problem in the South Atlantic and Caribbean Sea for most of a decade. Lionfish are strikingly colored, brightly striped and venomous. They can quickly populate an area and decrease native populations through either eating or chasing them away.
Black tiger shrimp are a relatively new phenomenon. A few were captured each year beginning in 2006, but the numbers rose significantly in 2011. More than 60 of the shrimp were brought by shrimp boats to one dock alone in Louisiana and the first captures off Texas' coast were reported. Black tigers are the largest species of shrimp in the world. Females are slightly larger than males and can grow to an average of about a foot in length and weigh close to three-fourths of a pound. Black tiger shrimp eat the same types of food as native shrimp species, but as they grow they also eat their smaller cousins.
"The biggest concern we have is what are the ecological impacts of these invasive species," says Dr. James Morris, an ecologist with the National Oceanic and Atmospheric Administration (NOAA) who has been working with lionfish for about 10 years and is now taking the lead in NOAA's efforts to study black tiger shrimp. "When you look across the history of invasive species, there have been some very extreme impacts that have resulted from invasions."
Invasive species often find themselves in foreign ecosystems devoid of the natural predators and diseases that kept their populations under control in their native ranges. Free of these challenges that plague native wildlife, invasive species can turn all of their energy toward feeding and reproducing. In some cases, the manner in which invasive species live can physically damage their adopted ecosystems to the point where it becomes poor habitat for native species.
Lionfish and black tiger shrimp, both native to the Indian and western Pacific Oceans, are noted for their aggressive feeding behaviors and hardiness. They can live in a wide range of water temperatures and salinities. These traits make them perfect, and dangerous, invaders.
Thus far, black tiger shrimp have left experts scratching their heads. No one seems to know where the shrimp came from, or what affect they will have on the three species of shrimp native to the Gulf of Mexico and, by extension, the $700 million shrimp fishing industry. "We just don't know what the long term impacts are going to be," says Gary Graham, Texas Sea Grant's Fisheries Specialist. "I don't know whether these shrimp will establish themselves in the Gulf of Mexico or play themselves out, but I think they could become a more serious problem than anyone originally thought."
Black tiger shrimp are an aqua cultured species in various places around the world, but their route to the Gulf remains uncertain pending genetic testing. There was an accidental release of black tigers from a research facility in South Carolina in 1988, but most of those animals were thought to have been caught by local fisherman by the early 1990s. No more tiger shrimp were reported caught until 2006. No aquaculture operation in the US grows black tiger shrimp. One popular theory holds that black tiger shrimp escaped into the sea from an aquaculture pond in the Caribbean that was breached by a hurricane in 2005. Others speculate that the shrimp hitched a ride from Asian to US waters in the ballast tanks of ships.
Leslie Hartman, Matagorda Bay Ecosystem Leader with the Texas Parks and Wildlife Department, is part of a casually organized group of people from various resource management agencies around the Gulf and South Atlantic who have banded together to perform genetic testing on the black tiger shrimp being caught around the nation's coastline. "We're trying to figure out where these animals came from," says Hartman. "If these are all genetically related back to the South Carolina shrimp, that tells us something about invasive species - that they will go into sort of a hiatus and then can re-surge. If the genetics show they are from different and unrelated populations, that tells us something else, like there was a second or third or fourth introduction. The more we understand about how invasive species spread, the more likely we are to intervene appropriately the next time."
Black tiger shrimp are susceptible to about 16 diseases, not all of them fatal, which can be transmitted to native shrimp and crabs. "The potential impact is roughly similar to the Europeans bringing smallpox to the new world," Hartman says. "They can put a hurt on the domestic shrimping and crabbing industries. Tiger shrimp are also active predators. Our native shrimp are active scavengers. As an active predator that is twice the size of its compatriots, its favorite foods are shrimp, crab and small bivalves. The most commonly collected small bivalve in Texas waters is the oyster. So between the diseases it carries and it being an active predator, the black tiger prawn can be a big issue."
Lionfish were most likely introduced to the Gulf through the aquarium trade - either as an accidental or intentional release from an aquarium. They have established themselves in the south Atlantic and Caribbean, and they were reported for the first time near Texas in mid-2011 at the Flower Garden Banks National Marine Sanctuary, located about 100 miles (161 kilometers) off the Texas-Louisiana border. Another was reported about 19 miles (31 kilometers) off South Padre Island in September 2011.
"The Gulf of Mexico comprises a wide array of habitats and anywhere you find structure you will find lionfish," says Morris. "Oil rigs provide high relief piling structures and I believe lionfish will recruit to these habitats in high densities. We have already seen high densities of lionfish around bridge pilings along the East Coast."
People visiting the coast generally play in the surf zones, which usually have barren sandy bottom, so lionfish-human interactions are not likely. Most interaction happen when people snorkel or dive around reefs or other structures. There are some reports that lionfish have acted aggressively toward humans, but Morris downplays these stories saying they are isolated. Lionfish are "curious animals," he says. The lionfish carries an impressive arsenal of venomous spines but uses them almost exclusively as defensive weapons. In humans, a lionfish sting can cause vomiting, fever, sweating and, in a few cases, even death.
Lionfish, which can grow to the size of a small football, are relentless predators that feed on recreationally and economically important reef fish like juvenile red snapper and grouper, and algae-eating species like parrotfish that keep reefs clean and healthy.