One of the main threats to ecosystem biodiversity is the introduction of non-native (i.e. exotic or invasive) species (see textbook p.188). Well-known examples of this are the introduction of the grey squirrel from North America into Europe, where it has led to the reduction in population density of the indigenous red squirrel, and the proliferation of the cane toad in Australia following its introduction in 1935 to eradicate the cane beet beetle.
Over the past decade the lionfish (Pterois volitans), a reef fish native to the Indo-Pacific, has become increasingly abundant in the Atlantic and Caribbean, in oceans where it has not historically been found. Current distribution includes the Atlantic coast of the USA, the Caribbean coasts of Central and South America, the Gulf of Mexico, the Greater Antilles, and the Leeward Islands. Scientists believe that the fish escaped from aquaria in Florida into United States coastal waters, and has since expanded in numbers due to a lack of competition and predation, along with abundant food supplies.
Lionfish are venomous and aggressive marine fish. They belong to the family Scorpaenidae: the genus to which they belong (Pterois) is characterized by red, white and black stripes (used to put off predators by indicatingtoxicity, or by breaking up body form), and elaborate pectoral and dorsal fins. All members of the Scorpaenidae have venom glands in dorsal, anal, and pelvic spines: the main function of these spines is to defend against
Pterois volitans (Lionfish)
competitors and predators. Lionfish have been shown to overpopulate reef areas and force native species to move to areas where conditions may be less favourable for them. They therefore pose a major potential threat to reef ecological systems on the east coast of the USA and Caribbean.
Lionfish are a benthic species – feeding at the bottom layers of the reef rather than in the water columns above (where pelagic fish feed). They suck small fish, crabs and other food off the surface of the reef, and can use their pectoral (side) fins to trap food. The largest of lionfish can grow to about 15 inches (0.4 meters) in length, but the average is closer to 1 foot (0.3 meters).
Download a factsheet about lionfish here.
For more information on the non-indigenous aquatic species off the east coast of America see the US Geological Survey site.
Effects of the invasive species
Lionfish have become the second most abundant species of fish from the Bahamas to North Carolina. In the Bahamas they feed on more than 41 species of fish, including commercially valuable species like grouper and snapper as well as fish that keep the reefs clean of algae. Pterois could have a significant impact on prey population numbers, thereby directly affecting complex food web relationships and having knock-on effects for many food chains. Reef deterioration and the collapse of food chains could therefore be direct results of the lionfish invasion.
Thorough and repeated removal of lionfish from invaded waters will be necessary to control their numbers (which are currently growing exponentially). Conservation groups are organizing hunting expeditions for Pterois, and other scientists are training reef sharks to hunt and eliminate the lionfish.
Lionfish are used extensively in cooking – they are tasty and succulent with a similar texture to grouper. Many recipes for lionfish exist, including fried lionfish, lionfish ceviche, lionfish jerky and grilled lionfish. Human consumption of lionfish may prove to be one of the best ways to reduce population numbers and aim for total eradication from the invaded waters.
Tasks Research and write about another example of an invasive species that has adversely affected native biodiversity.
What other factors cause a loss of biodiversity? (HINT: the mnemonic ‘H.I.P.P.O.’ helps to recall the various threats that biodiversity faces, with each letter representing a different threat.)
If you live on the eastern seaboard of the USA, the Caribbean, or other areas in its distribution zone, keep your eyes open for lionfish. To report sightings of the fish use this report sheet. Knowledge of the distribution of the species will be essential in planning ways of removing this unwanted invader.
If you live in an area where lionfish are commonly available, find a recipe and prepare a fish for family or friends. Promote this fish as an alternative to other edible species and help reduce population densities in areas where the fish are found outside their natural distribution.
Suggested answers For example: red-clawed signal crayfish (Pacifastacus leniusculus), a large, aggressive American species which has wiped out almost 95% of the native UK white-clawed species (Austropotamobius pallipes) since it was introduced to the country in the late 1970s; human activity has led to an increase in numbers of crown of thorns starfish which eats coral reef leading to extensive damage (e.g. Great Barrier Reef).
Habitat destruction or fragmentation; Invasive species; Pollution; Population growth (human); Overhunting (see pages 188 and 211 of textbook).