Louisiana Waterways Under Siege: The Giant Applesnail Invasion
Jan 01 2021

Louisiana Waterways Under Siege: The Giant Applesnail Invasion

By: Michelle Nicholson

Our South Louisiana wetlands have long been heralded as the most fecund ecosystem in the United States, but these wild places of refuge are welcoming hosts to newcomers as well as natives. Invasive species disrupt, destabilize, and potentially threaten the vitality of the wetlands they depend upon and call home—for "invasive" species are, in fact, making themselves at home, wherever they go.

For example, it has been a century since our bayous became clogged with water hyacinths, thanks to the World Cotton Expo of 1903. The Louisiana Works Progress collection includes an archived photo of a steamboat struggling to traverse a hyacinth-blanketed bayou in 1920. By the 1950s, the New Orleans Department of Public Buildings and Parks was struggling to manually remove this choking "malodorous" overgrowth in Bayou St. John, by the truckload, and the Sewerage and Water Board, which was losing equipment in the battle, wanted nothing more than to bury and cover the canals.

Today, the National Park Service has an entire page dedicated to the water hyacinth, "a GREAT invasive species but a challenging plant to control," although some may disagree with labelling a stinking plant that has shut down canoeing in the Barataria Preserve as "GREAT." On the other hand, Airboat Adventures in Lafitte, Louisiana, prefers to praise the plant's "stunning flowers" when sharing what is "iconic" in Bayou Barataria, before moving along with the tour.

In recent years, talk about invasive species in Louisiana wetlands is rapidly expanding from a quiet behind-doors mutter among government agencies to a cry of alarm by the media about the giant applesnail—the Pomacea maculata, or island applesnail, to be specific. The island applesnail is a native South American freshwater mollusk, but snails have long been a favorite tank-cleaner among aquarium keepers, which is how they were brought to the U.S. Applesnails grow to be apple-sized and are voracious, omnivorous eaters, so they do not perform as well as some others, such as Nerite and Ramshorn snails, in aquariums. By the 1980s, applesnails were being dumped. Thanks to this aquarium dumping, the applesnail invasion was first discovered by U.S. Fish and Wildlife in 1989 in Palm Beach County, Florida.

The water hyacinth, a native of South America, was introduced to Louisiana wetlands in 1903. Here, we see how successfully the species takes total control of waterways. Photo Credit: Wikimedia/KenB

Now, according to the U.S. Geological Survey, applesnails have spread to 76 hydrological units, or watersheds, along the entire Gulf Coast: from Texas to Florida, and as far north as the Mississippi, Atchafalaya, and Red Rivers confluence. In 2006, they were first sighted in Gretna, Louisiana, in the Verret Canal, which is connected to the Barataria Preserve by the Intracoastal Canal. By 2008, the applesnail was popping up in ponds and bayous along Lake Pontchartrain's Northshore. In 2012, applesnails were infiltrating pump houses and drainage ditches around Lake Maurepas. By 2015, they had penetrated New Orleans's City Park, where you will now find the edges of the park's isolated bayous littered by piles of empty applesnail shells.

Such massive unburied graveyards of applesnails might appear to indicate a holocaust. However, applesnails are one of the most successful animals on the planet. According to Dr. Phil Bucolo, an aquatic biologist at Loyola University New Orleans, they are simply "outcompeting" all of their neighbors. Besides eating anything and everything at their trophic level, they spend their lives submerged in water, safe from predators, only emerging at dusk and dawn to lay eggs—and they are prolific breeders.

According to a 2017 study conducted by a coalition of Gulf coast universities, just one applesnail clutch holds an average of 1,500 eggs. Over a lifetime of three years, a single snail may produce 54,000 eggs. Basically, even if a mere 0.01% (or 1 in 10,000) eggs survives, a single snail will replace herself with three to five offspring in her lifetime—and this number is probably an underestimate of snails' reproductive rates in the southern USA, where warm weather means a longer breeding period. Ultimately, every applesnail shell washed ashore represents exponentially greater numbers of them in the water—and exponentially more problems for the creatures competing with them for life.

There is no question about the havoc applesnails are wreaking in South Louisiana wetlands. According to the Louisiana State University AgCenter, their consumption of both vegetation and the eggs of amphibians in their habitats makes inhospitable waters for ducks as well as fish—bad news for a state nicknamed Sportman's Paradise. In 2020, South Louisiana's extensive applesnail colony succeeded in decimating a 50-acre field of rice and shutting down production in crawfish farms in three parishes. According to LSU's sugarcane entomologist Dr. Blake Wilson, even the farms and harvests that were not completely halted suffered "revenue reductions of as much as 50 percent."

Not only Louisiana's wetlands, but the Louisiana coast itself is embattled. The applesnail devours plants that hold together the coastline and transforms clear water into turbid algae-infested waterways, or water that Dr. Bucolo warns may host the kinds of dangerous algal blooms creating dead zones in Lake Pontchartrain and at the mouth of the Mississippi River. As was the problem with water hyacinths, applesnails seem to have the potential to smother all other life in their eco-communities, causing a big stink—and they seem to be collaborating with water hyacinths in that endeavor as their colonies grow.

In 2008, the invasive species coordinator for the Barataria-Terrebonne National Estuary Program, Michael Massimi, noticed that applesnails were attaching eggs to boats traveling the Intracoastal Waterway, or "hitching a ride on the superhighway" connecting previously uninvaded wetlands across the entire Gulf coast. Water hyacinths also traveled, conveniently, via the Intracoastal Waterway. Dr. Bucolo has noticed that applesnails seem to be developing a preference for depositing their eggs on water hyacinths—which always float above the water and will therefore keep their eggs dry, increasing their likelihood of survival—rather than the wood and plant structures they have preferred in the past.

Applesnails, apparently, are highly adaptive—even smart. We need to be smarter.

More often than not, in Louisiana, where there are water hyacinths, there are applesnails. To outdoor recreationists, this may seem a mere nuisance, if a problem at all. However, these colonies present a growing threat to coastal and wetland restoration projects as well as to the Department of Environmental Quality. For example, the Riverbend Oxidation Pond, in St. Bernard Parish, part of the Coastal Impact Initiative, is an essential source of fresh water to the Poydras-Verret Wetlands, with the ultimate goal being reforestation of the cypress-tupelo swamp that once thrived there. However, the water hyacinths and applesnails are engaged in their own growth initiative, and since 2018, the St. Bernard Department of Environmental Quality has struggled to control the invasion at the Riverbend Oxidation Pond.

Water hyacinths cover the surface of the pond, disrupting the natural cycle of oxidation; applesnails clog the channels, blocking UV lights and slowing the flow of water. Jake Groby, the Superintendent of the Environmental Department's Water & Sewerage Division, reports that they must regularly manually remove the water hyacinths, but the applesnails are a more complicated problem with no obvious solution. The result of the applesnail infestation is that for the past two and a half years, the Riverbend Oxidation Pond has been discharging improperly treated waste (i.e., water with excessively high levels of coliform bacteria) into the wetlands, just on the other side of the 40 Arpent levee.

Dr. Chris Murray, a vertebrate toxicologist at Southeastern Louisiana University, says citizens should not be terribly concerned by these exceedances, as they are unlikely to enter the human water supply. However, Dr. Bucolo argues that vast devastating disruptions may occur within eco-communities in a three-year period, and that the potential combined impacts of the water hyacinths, applesnails, and discharge of waste that fails to comply with today's relatively lax environmental regulations warrant investigation.

Limpkin were first sited in Louisiana in 2017 and were spotted breeding at Lake Houma in 2018. There are still few on record though—this feathered-friend was spotted in Florida. They are a vision of hope for our wetlands to adapt to applesnails. Photo credit: Flickr/Melissa McMasters

Groby also asserts in an email that, in St. Bernard Parish, the applesnails "are in the drainage system as well from end to end … All parishes seem to have them." Beyond incurring the malfunction and failure of the Riverbend Oxidation Pond, the applesnail colony, then, presents a farther-reaching threat to health and restoration. Discharging treated waste material into freshwater wetland systems has become a widespread practice, not only as a part of the Central Wetlands Assimilation Project, but throughout South Louisiana—a practice pioneered and promulgated by scientists such as Dr. Gary Shaffer, a wetlands ecologist at Southeastern Louisiana University.

When asked about how the applesnail is impacting similar operations with which he is involved in the Central Wetlands, Lake Maurepas, Hammond, and Ponchatoula—all places identified as infiltrated by applesnails—and what measures they are taking to control their populations and protect these restoration initiatives, he was unavailable for comment. The Louisiana Department of Environmental Quality was also unavailable for comment. Groby believes that "the state has been caught off guard" by the applesnails and the infrastructural problems they are causing. And no one has yet to examine whether applesnails' clogging New Orleans's drainage system (along with the water hyacinths) is related to pump failures and the noticeable increase in flooding that started in 2017.

We need to be smarter.

Dr. Bucolo posed a provocative question: How can we consider established populations invasive? Without a doubt, these colonies are here to stay. Killing their massive populations might prove to be even more deadly, just as one of Dr. Bucolo's recent (yet-to-be-published) studies showed that chemically killing water hyacinths rapidly depleted oxygen in the water and created a dead zone. Killing is a solution that, simply put, only leads to more death—a literally bigger stink—never mind that blanketing applesnails with salt or copper means adding those elements to our freshwater environments, which may also add to the death toll.

Every creature represents a vital link in the great rhizome of life—most obviously, as a part of the food web. But the applesnail has evaded natural predators such as the snail kite by migrating to the Louisiana coast and wetlands. Many humans do find snails appetizing, and applesnails are landing on tables throughout the world, particularly in Asia, or in Cajun homes—in cultures that are accustomed to living closely with and off the land. Unfortunately, because of what applesnails are eating in our drainage systems (rat feces), their populations in the Gulf of Mexico region carry rat lungworm, a potentially fatal parasite. Fully cooking the snails before consumption kills this parasite, but eating them, unless necessary for survival, is ill-advised.

As of now, our best course of action is to suppress their reproduction before they fatally tip the natural balance of the eco-communities that applesnails call home. Dr. Bucolo encourages people to manually scrape applesnail eggs into the water, where they are much less likely to hatch, whenever and wherever we find them: the shorelines, piers, and boats in backyards and parks under their care. Farmers may protect their crops by removing plants and structures that applesnails might use to lay eggs from the perimeters of their fields. Local governments may aggressively manually remove and reduce water hyacinth colonies as a strategic defense.

In the meantime, some people have even decided to profit from the invasion by collecting, cleaning, polishing, and embellishing empty applesnail shells, for sale on Etsy. A local poet collects them while kayaking in City Park and converts them into fun little poetry-filled fortune cookies.

We certainly need to be smarter, but nature may still prove to be smartest over time.

In Asia, carnivorous ducks have been introduced to agricultural practice, thereby reducing the applesnail population in those areas by 95 percent. However, such artificial human introduction of new plants and animals to ecosystems often means transforming creatures of beauty into "invasive species" when they suddenly disrupt the intricate balance of local eco-communities. Fortunately, other animals may adapt more quickly than we: The limpkin, one of two avian applesnail predators, arrived and began breeding in Terrebonne Parish, at Lake Houma, in 2018. And like the bright purple spring of the hyacinth's bloom and the algorithmic appeal of applesnail shells, the limpkin is an absolute cutie—an invisible tug on heartstrings—especially when spotted passing, beak to beak, a feast of applesnails among friends.

Cover photo:

The shells of dead applesnails litter the old bayou circumnavigating the interior of City Park in New Orleans, and their bubble-gum-colored clutches dot the water foliage, cypress knees, and decked overlooks in the park's Couterie Forest, where this photo was taken in October 2020. Photo by Michelle Nicholson.



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