By Mark Young
European explorers led by Christopher Columbus were actually searching for a sea route to Asia when by luck they discovered the Caribbean and the Americas. This wasn’t so lucky for the various native populations, however; they couldn’t defend themselves against conquest, but the most devastating import was biological. Where the people of the three known continents had long been exposed to each other’s diseases and developed a strong immunity, the cultures that the “Columbuses” discovered were powerless against the import of smallpox, measles and influenza. Mere contact killed millions of indigenous people.
In a sense you could say that throughout history subsets of man have been an invasive species. And wherever we humans have gone, nature has been along for the ride.
People tend to think of “invasive species” only in negative terms, but the phrase has several degrees of definition. Toward the “OK” scale it refers to “introduced species or nonindigenous species that are rapidly expanding outside of their native range.” A not-so-OK connotation is, “alien species whose introduction or spread threatens the environment, the economy, and/or society, including human health.”
Degrees of the definition are appropriate. For example, an argument can be made that the introduction of most exotic species has richly enhanced biodiversity. Consider traveling plants; more than 4,000 species introduced into North America during the past 400 years make up nearly 20 percent of our current plant biodiversity. And, with no evidence, according to some biologists, that a single resident species has been driven to extinction. In other words, with some pesky exceptions, plants that invade fit in.
As divers we tend to think negatively about the arrival of nonindigenous marine life, yet the opening of the Suez Canal in 1869 introduced 250 new fish species into the Mediterranean from the Red Sea, reportedly resulting in only a single extinction. So there’s that.
On the other hand, who wants the Burmese python at the top of the Everglades food chain? (Have you seen the YouTube video of the snake that exploded while digesting an alligator?) Their numbers in the Glades are estimated at more than 100,000, growing fast, and pose a threat to natural balance in a truly spectacular ecosystem — all because a few pets outgrew their welcome. Perhaps the Nile monitor lizard, an African heavy that grows to 7 feet (2 m) in length can give the pythons a run for the top; they’ve also established Florida residency. Kind of makes the U.S. invasions of zebra mussels and Asian carp seem tame.
This month’s cover feature is an update on the Atlantic/Caribbean invasion of lionfish, another pet let loose. There’s no debate that this has the possibility of an environmental disaster. One hope against it is the commercial potential of lionfish as a culinary dish; that would at least put something above them in the food chain. Another possibility is whatever mechanism keeps them in check in their far-Pacific homeland, something that is being studied to determine.
However this plays out, we’re about to see in the extreme how well natural balance can occur where it must, while we humans continue to move nature past the geographic boundaries that once contained the Earth’s biota, and into our own backyards.
