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Second Story – Spring 2015
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The Wonders of Discovery: Reviving Interest in Natural History
VOLUME 29, NUMBER 1, SPRING 2015             

By John H. Tibbetts                                                                       back to main story

Naturalists keep watch over biological invasions

Scientists see growing evidence that climate change is altering the range of many wild organisms, including aquatic species that have recently arrived in the Carolinas for the first time.

Naturalists are keeping watch over changes in ranges of numerous species. The methods of field monitoring and taxonomy—natural history—allow scientists to locate, track, and understand non-native species and their impacts from place-to-place.

David Knott, a Charleston-based consulting biologist for natural-resource agencies, has documented more than 65 non-native invertebrate species that have moved into South Carolina freshwater and saltwater ecosystems over the past three decades, though none has shown to be a nuisance. Of the 65 species, 13 are fresh-water, 48 are brackish to marine, and four are semi- or fully-terrestrial in nature.

Nine of those 65 species expanded their range to South Carolina from regions to the south partly because of warming waters here, says Knott.

A much larger fraction of those 65 new species in South Carolina were originally introduced to tropical areas of the western North Atlantic from other tropical regions around the world.

“The non-natives became established in waters to our south and have gradually, or in some cases abruptly, moved into South Carolina,” says Knott. “That dispersal may be attributed to [warmer] temperatures that allow those species to creep north until they reach the limit of their current tolerance range.”

Climate conditions, in other words, appear to allow some non-native species that have gained a niche in regions to the south—the eastern coast of Florida, the Caribbean, and the Gulf of Mexico—to stretch their range northerly, moving into the Carolinas.

As a non-native species moves into a new habitat, it can become invasive and out-compete natives for food and other resources. Or the non-native species might have left behind predators that kept its pop-ulation under control in its former habitat. As a result, the non-native species population can grow very rapidly.

The red lionfish (Pterois volitans) is one example of that problem. The invasive red lionfish, originally a native of the Indo-Pacific region, has expanded its range from eastern Florida farther north to the Carolinas, following the warm Gulf Stream. This range expansion could be influenced by climate change, scientists say.

The red lionfish has been called the most invasive reef species in the world, gobbling up prey that are unfamiliar with its hunting techniques. This fish has become a hugely abundant and destructive predator in the western Atlantic and the Caribbean.

Some non-native species arriving from locations farther south, however, haven’t yet survived South Carolina’s winter temperatures.

In 2006, a non-native, tropical green mussel (Perna viridis) was found in South Carolina for the first time. The green mussel is a saltwater pest that invaded Florida thousands of miles from its Asian native habitat in coastal waters along the Persian Gulf to Hong Kong.

Green mussels grow large; they are hand-size at full maturity. In Florida, they have proliferated in dense layers on marine facilities and boats. Their accumulated weight has sunk navigational buoys and floating docks. Colonies of the mussel have clogged water intakes in Florida power plants.

But not long after the mussel arrived in South Carolina, it died off because of cold winter events, especially during the winter of 2009-2010, and did not return.

That especially cold winter also dramatically knocked back populations of two other tropical marine invertebrates that had invaded South Carolina: the green porcelain crab, Petrolisthes armatus, and the titan acorn barnacle, Megabalanus coccopoma. These two species have apparently not returned in significant numbers to South Carolina.

But will their populations expand again in South Carolina as the ocean warms?

That could depend on the intensity of winter cold extremes along the coast. Bitterly frigid weather appears to be the limiting factor for the northerly expansion of some tropical species.

The number of very cold days in South Carolina’s coastal waters has increased in frequency since the early 1990s, although average annual temperatures have been rising over the same period, scientists say. These winter cold snaps are largely driven by a long-term trend in ocean circulation—called the North Atlantic Oscillation—that drives Arctic blasts southward, scientists say.

But are these cold extremes in the region also enhanced by climate change? Could global warming somehow help drive Arctic blasts farther south along the Atlantic coast? Scientists are trying to answer those questions.

Yet there are fewer and fewer professional naturalists with hard-won observational skills and experience to track non-native species and spread alarms when those species become biological invaders.  

“We need more people who know which native species are out there,” says Knott. “If you don’t know which species are native, then you can’t recognize which species don’t belong there and could become invasive. If you can’t recognize invasive species early, you can’t control them early.”

Last updated: 6/24/2015 12:58:09 PM
Second Story – Spring 2015


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