Louisiana: A Hotspot for Species Introduction

Most large rivers host extraordinary communities near their mouths. Human societies tend to be more culturally diverse at these strategic positions; their economies and histories tend to be more far-reaching and tumultuous. The meeting point of vast interior hinterlands with large exterior water bodies—where rio joins mar at the brink of continents—also creates rich, productive natural ecosystems; in Louisiana, these environments include our inland wetlands and swamps as well as the estuaries where fresh and salt water mix. To scientists, urbanists, poets, and engineers, these port cities and their environs comprise arguably the most fascinating places on Earth. But communities at the mouths of great rivers are also more vulnerable to invasion by species that did not evolve under these specialized conditions. Centuries of shipping merchandise and raw materials from suppliers in one part of the world, through ports and waterways to consumers in other parts of the world, have seen the accidental relocation of thousands of species to new environs.

Louisiana, especially the porous netherlands of the southeast, forms an especially vulnerable site for species introduction. Port activity accounts for much accidental introduction, and Louisiana is home to one of the world's great ports, New Orleans, the gatekeeper of the Mississippi River and entry point to the richest valley of the richest country on Earth. It is neighbored by dozens of smaller ports, perched on nearly every waterway that penetrates the Deep South, as well as larger facilities in nearby Houston, Gulfport, and Mobile. Louisiana's mild, humid subtropical climate allows many incoming species to survive upon arrival; of these, some thrive by exploiting niches in the state's diverse ecosystems (made vulnerable by the large quantity of disturbed land) and then spreading. Railroads, canals, roads, and interstates crisscross the region, performing critical economic functions but also serving as conduits for this diffusion. Even the waters of the Mississippi carry species introduced in northern ports to Louisiana’s waterways and estuaries downstream.

As a link between the American heartland and world beyond the Gulf of Mexico, Louisiana is a hotspot for invasive species. Consider these figures:

  • Of the world's 100 worst invasive species identified by the Fondation d'Entreprise, at least 13 occur in southern Louisiana. Those species are the Asian tiger mosquito, Formosan termite, zebra mussel, water hyacinth, feral cat, cogon grass, house mouse, nutria, rabbit, kudzu, rat, red imported fire ant, and feral pig.
  • According to the US Geological Survey's database of nonindigenous aquatic species, Louisiana has more introduced aquatic plants (32) than any other state save Florida, which has 45. Louisiana has almost 2 times the average number of introduced aquatic plants per state.
  • The Nature Conservancy's "Dirty Dozen" list of most destructive invasive species in the US cites four (33%) occurring in Louisiana, a state that comprises 1.4% of the conterminous US land area. Those species are the zebra mussel, tamarisk, hydrilla, and Chinese tallow.

Louisiana bears a disproportionate share of the ecological and economic burden imparted by invasive species, in a natural and built environment that offers so many unique aspects to the nation and world.