Pomacea insularum is now Pomacea maculata!

P. maculata shells

Dr. Romi Burks from Southwestern University emailed me recently and asked me to “alert people about to the paper by Ken Hayes and his colleagues” that changes the taxonomy of the Island Apple Snail. After Dr. Robert Dillion of the College of Charleston suggested the same thing months ago, I published the abstract of the excellent and exhaustive report Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae in the Recent Reports section of this blog. However, I must admit some defiance (laziness?) to changing the scientific name throughout this site. My poor, old brain just wishes the taxonomists would make up their minds, so I would not have to relearn scientific names. I know I’m not alone. However, as Romi writes, “What’s in a name, one might ask? A whole lot!!” So, it’s official – – Pomacea insularum is no more, or as Ken Hayes et al put it: “Ampullaria gigas Spix, 1827 and Ampullaria insularum d’Orbigny, 1835 are herein synonymized with P. maculata.” Sorry, I’m just the messenger!

Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda) by KENNETH A. HAYES1,*, ROBERT H. COWIE1, SILVANA C. THIENGO2, and ELLEN E. STRONG3, 1Center for Conservation Research and Training, Pacific Biosciences Research Center, University of Hawaii, 3050 Maile Way, Gilmore 408, Honolulu, HI 96822, USA,2Instituto Oswaldo Cruz/Fiocruz, Av. Brasil 4365, 2104-900 Rio de Janeiro, RJ, Brasil,3Smithsonian Institution, National Museum of Natural History, P.O. Box 37012, MRC 163, Washington, DC, WA 20013-7012, USA, Zoological Journal of the Linnean Society, Volume 166, Issue 4, pp 723–753, December 2012

http://onlinelibrary.wiley.com/doi/10.1111/j.1096-3642.2012.00867.x/abstract;jsessionid=EFB0C1573E4E5BA869B0E679F7F3642F.d04t01?deniedAccessCustomisedMessage=&userIsAuthenticated=false

_____________________________________________________

New USGS Maps Depict Ranges of Exotic Pomacea in the Continential U.S.

Pomacea insularum map 03.19.2013 USGS

USGS Fact Sheet for Pomacea maculata (insularum)

http://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=2599

_____________________________________________________

P. canaliculata map 2.15.2013 USGS

USGS Fact Sheet for Pomacea canaliculata

http://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=980

USDA Profile for Pomacea canaliculata

http://www.invasivespeciesinfo.gov/aquatics/applesnail.shtml

____________________________________________________

How is the Island Apple Snail spreading so rapidly in Florida?

According to FWC’s data presented at the end of my last post, the Island Apple Snail (Pomacea insularum) was found in less than 1% of Florida’s public waterbodies in 2006. Five years later, its range has exploded to 22% the state’s lakes and rivers. How is that possible for an animal that moves an average of only 14 meters/week (Darby et al., 2002)? None other than Charles Darwin (1859) was also “perplexed much” when contemplating wide distribution of certain freshwater snail species among the distant Pacific Islands.

There are two modes of range expansion for organisms: active and passive. The active mode for mollusks is at a proverbial “snail’s pace.” Nevertheless, snails are common globally, including desert oases and newly formed volcanic islands. Clearly, mollusks possess an extraordinary capacity for passive means of dispersal. In the case of P. insularum, I have witnessed them using temporary buoyancy to move easily with the waves across lakes or with the current of creeks to rapidly float downstream. Such passive mobility can easily explain dispersal within a given watershed. However, I have also seen this primarily-aquatic species quickly and inexplicably appear in newly-constructed, isolated ponds. Passive dispersal by human activities is well-documented and, therefore, usually blamed, but I wonder. Range expansion in such far flung areas just seems too commonplace. There cannot be that many hobbyists recklessly dumping aquaria!

Charles Darwin (1859) conducted an experiment on a theory proposed by Lyell (1832) that external transport by birds is the most likely passive dispersal mechanism of freshwater snails: “I suspended the feet of a duck in an aquarium; where many ova of freshwater shells were hatching; and I found that numbers of the extremely minute and just-hatched shells crawled on their feet, and clung to them so firmly that when taken out of the water, they could not be jarred off, though at a somewhat more advanced age they would voluntarily drop off. These just-hatched mollusks, though aquatic in nature, survived on the duck’s feet, in damp air, from twelve to twenty hours; and in this length of time a duck or heron might fly at least six or seven hundred miles, and if blown across the sea to an oceanic island, or to any distant point, would sure to alight on a pool or rivulet.”

Many researchers after Darwin have been equally “perplexed” by the rapid and/or long distance dispersal of slow-moving mollusks, but a scientific consensus is developing. Vagvolgyi (1975) concluded that small body size facilitated the dispersal of land snails across broad expanses of ocean: “Support to the hypothesis is provided by the facts that land snails have been recovered from the plumage of birds [and] that recently formed volcanic islands have been colonized predominantly by minute land snails.”

In a study of 50 springs widely scattered across the arid regions of Australia, Wilmer et al. (2008) determined that “short range dispersal of aquatic snails occurs via active movement facilitated by aquatic connections among springs while long-range dispersal is likely facilitated by an animal vector (phoresy).” Aubry et al (2006) stated that passive dispersal of an invasive snail in France relied on “a behavior, called the ‘climbing reflex’ – – one of the main and most efficient features in the process of passive dispersal.”

Clearly, the theory that birds transport aquatic snails is not new.  In fact, it is no longer a theory but has been demonstrated convincingly, both experimentally and by field observations. “The pulmonate land snail Balea [has]even managed to travel over thousands of kilometers of open ocean, from Europe to the Azores and the Tristan da Cunha islands, and back again” (Gittenberger et al., 2006). In the case of the Island Apple Snail, I wonder if the “climbing reflex” is innate behavior for newly-hatched juveniles. It would certainly be easy for such small snails to attach to the legs of wading birds frozen in their common fishing stance.

To test that theory, I went back to my favorite experimental site, Wellman Pond, and placed 30 bamboo stakes with diameters similar to those of the legs of wading birds near hatching egg clusters of P. insularum. Upon return, I carefully inspected each stake and found only one juvenile snail. Quoting Gittenberger (2012) again, “Long-distance dispersal implies a series of unlikely events. However, time is available and a single snail may be sufficient for a successful range extension.” In Florida, the distance from lake to lake is relatively short. It seems reasonable to conclude that the rapid range expansion of the Island Apple Snail is via passive dispersal on the legs wading birds. Posted by Jess Van Dyke

Does Pomacea’s Aerial Respiration Requirement Determine Environmental Impact?

Aerial respiration of Pomacea via siphon (Jess Van Dyke)

Though Apple Snails are freshwater inhabitants, they are clearly amphibious. Pomacea possess combed, gill-like structures (ctenidium) for aquatic respiration and lung-like pulmonary sacks for aerial respiration, as well as buoyancy regulation. When dissolved oxygen levels are high (5-6 ppm), the snails remain mostly underwater, but when low (1-2 ppm), they rely on their siphons and “lungs” to breathe fresh air (San Martins et al., 2009). In any case, all Pomacea regularly come to the surface to ventilate their “lungs.” Such behavior is obligatory.  Preventing aerial respiration negatively affects activity, feeding, and survival (Seuffert and Martín, 2009). They must occasionally take a breather!

Darby et al. (2002) reported that Apple Snails prefer to inhabit shallow water areas ( < 50 cm) because of the need to breathe atmospheric air without expending a large amount of energy to move to the surface. Darby (1998) also suggested that unconsolidated organic material may restrict movement into deep water. However, recent observations of healthy Pomacea as deep as 14.6 m (48’) in Apopka Spring indicate that depth alone is not a deterrent to the snails (Bernatis, 2010). Seuffert and Martín (2009) have concluded that Pomacea are unevenly distributed relative to the access to air – – concentrated less than 2–4 m from the nearest emergent substrate. Simply put, Apple Snails need easy access to emergent plants (or other structure), so they can crawl up and catch a breath of fresh air.

According to the annual survey by FWCC, Pomacea insularum is now present in 22% of Florida’s public lakes and rivers (see below). The mystery in Florida is why this invasive, exotic snail will strip one lake and leave the vegetation relatively unaffected in another. Perhaps, three physical features of lakes play important roles: shoreline development, average depth, and mean slope. Shoreline development (SD) is simply the ratio of the length of the shoreline of a lake to the circumference of a circle with the same area as that lake. The higher the SD ratio is the more complex the shape of the lake. Average depth is self-explanatory, and mean slope is the proximity of bathymetric contours to one another. Taken together, these parameters determine the extent of the littoral zone and the abundance of emergent vegetation.

A relatively small, shallow lake with a gradual bathymetry but a complicated shoreline would seem to provide the best habitat for Pomacea insularum. In such a lake, on a per area basis, food would be more abundant; emergent vegetation would always be near for aerial respiration (and egg deposition); and dissolved oxygen would tend to be high, unlike in a deeper lake with an anaerobic hypolimnion. In short, a greater percentage of the lake would be within 2-4 m of substrate that Seuffert and Martín (2009) suggest is Pomacea’s preferred habitat. The greater the density of Pomacea insularum, the more likely the snail population could consume all of the aquatic vegetation in a given lake. Let’s see how this theory plays out. Posted by Jess Van Dyke

Annual Survey of Florida’s Public Waters  for Pomacea insularum by the FWC:
               Year

Number

        Area (ac)

2006

4

4779

2007

45

680301

2008

50

691045

2009

75

752529

2010

86

736263

2011

102

826860

Ebro Delta: The Exotic Apple Snail’s Bridgehead in Europe

The Ebro Delta (350 km2), located in Tarragona at the southern end of Costa Dorada, is the largest wetland in Catalonia and is the second most important natural wetland habitat in Spain. About 8,000 ha of the delta are natural park sites, part of the Natura 2000 network of the European Union. The delta has high biodiversity and productivity, excellent fish and wildlife habitat, and important water purification and storage functions. Plant diversity is extremely rich with 515 species catalogued. Large pools surrounded by giant reed beds occupy the coastal portions. No wonder the Ebro Delta is the second most important bird habitat in Spain. Economic activities include agriculture, fisheries, aquaculture and tourism. Rice cultivation, however, is the dominant use.

On August 1, 2009, the Island Apple Snail (Pomacea insularum) was first documented on the European Continent. Its conspicuous, bright-pink egg clusters were detected on shoreline vegetation along a small irrigation canal, adjacent to a fish farm in the Ebro Delta. The range expansion of the exotic snails was explosive. Within a month, they had colonized half of the interconnected canals in the northern half of the delta (up to 5.1 egg masses m-1) as well as the main river channel (up to 6.2 egg masses m-1). After reviewing the literature, local experts recognized the great potential of widespread economic and  environmental damage.

Government agencies quickly implemented plans to eliminate the pest manually, mechanically and chemically hoping to avoid harmful effects on agriculture and native biodiversity. All emersed vegetation from 16 miles (26 km) of shoreline in the initial area of infestation was harvested and incinerated to no avail. The desiccation of 9,500 hectares of the delta for five months at a cost of 3.5 million € in attempt to eradicate the snails proved fruitless. In spite of these and other extreme measures, “the ability of the Island Apple Snail to thrive and disperse in the Ebro Delta shows that this bridgehead is firmly established,” writes Miguel Angel López of the Catalonian Government Environmental Department.

I have been in communication with a biologist who is currently assisting the frustrating struggle to stem the Island Apple Snail’s invasion of Europe: “The Environmental Department has been hand-collecting adults, putting barrier traps in the irrigation canals, destroying egg clutches, and burning shoreline vegetation in non-sensitive areas to remove egg substrate. They are now using saponins as well. The snail is occupying an area of the delta where there are mostly canals for habitat. The Environmental Department has mapped about 240 km (150 miles) of canals which are infested. We regularly have sustained temperatures of 9 or 10º C during winter here with occasional drops below zero and there has been snow here during two of the last five years, and they seem to be doing just great! Copper is not permitted as there are native bivalve species sharing the irrigation canal habitat. Baits are problematic as the current in the canals rapidly disperses them. Despite the Environmental Department’s efforts with a crew of 30 people, there seems to be no end in sight. The bottom line is more funding is needed to get ahead of this pest. Any suggestions from your experiences would be appreciated.”

O.K., I’ll give it my best shot: Clearly, the situation is dire; the wetlands of an entire continent are at stake. In my opinion, the ultimate solution is biological control via some selective pathogen, though such an organism will not be easy to find (or create). At present, containment is paramount. Accidental transport of the exotic snails to other aquatic sites must be prevented. In my experience, anglers with boats on trailers are most often responsible for the inadvertent dispersal of invasive, aquatic species. In the case of Pomacea, however, aquarium hobbyists have played a major role.

Within the Ebro Delta, I suggest that you focus on Pomacea’s two key vulnerabilities: the conspicuousness of its eggs and its vulnerability to chemical attractants. Continue to collect eggs, as much as manpower will allow, and possibly make some money to subsidize your control efforts. Biotechnology companies in Taiwan are spending huge sums to develop technologies to extract the anti-oxidant Astaxanthin from Pomacea eggs. These companies estimate that the value of the anti-aging, skin care products based on that active ingredient could reach over $400,000,000 annually. Natural Astaxanthin is currently priced at $7000/kg (not a typo). Maybe, a Spanish biotech firm would like to participate and fund the collection of Pomacea eggs in the Ebro Delta!

Regarding baiting, do not underestimate the chemoreception capabilities of the Island Apple Snail. Even with some flow, Pomacea can be drawn to the right attractant. For collection (or poisoning), bait stations make sense. I have shipped Miguel one of our traps with non-toxic bait to test. By doing so, I am not
suggesting that trapping and collecting snails along 240 km of canals is practical. However, with an attractant bait that is also toxic, progress could be made in reducing the population of adult snails. I am in touch with a company that produces an innovative, plant-derived molluscicide, and am eager to incorporate it into the bait we produce for laboratory testing. I will let you know how that goes. Good luck with your battle, Miguel! Posted by Jess Van Dyke

For more information, contact:

Miguel Angel López

Catalonian Government Environmental Department

Miguel.Lopez@gencat.cat

False Hope of the Boom-and-Bust Model

It has been a long time since my last post. The problem has not been “writer’s block” but the lack of an interesting topic. It has been very quiet in the southern U.S. regarding exotic Pomacea. Though the USFWS in Alabama continues to struggle against Pomacea insularum at two locations, officials in the rest of the South seem complacent regarding exotic Pomacea. In Florida, the official dogma is that “they tend to boom-and-bust without causing much harm. Besides, they have already spread everywhere.” I am less sanguine.

Regarding the boom-and-bust rationale for official inaction, Dr. Daniel Simberloff and Leah Gibbons (2004) said it best: “Substantial populations of invasive non-indigenous species occasionally collapse dramatically. Although disease is often invoked, the causes are rarely studied experimentally and/or quantitatively, and some collapses remain quite mysterious. Except for the few species in which spontaneous collapse has been repeatedly observed, the possibility of such an event is unwarranted as a potential rationale for a do-nothing approach to management.”

In an exhaustive study of the impact of alien species in the Mediterranean Sea, Dr. Charles Boudouresque et al. (2005) concluded, “The boom-and-bust model predicts the eventual decline of the invasive species and the recovery of the native ecosystem. In fact, species introductions are irreversible, even at a geological scale, and the natural decline of introduced species is quite uncommon. Data have been misinterpreted, leading to the generalization of the probably rare boom-and-bust model.” The graph below depicts the typical population volatility of an introduced species which is not to be confused with a permanent “bust.”

Often, the interaction between a species’ population size and its habitat is subtle. Populations fluctuate due to density-dependent factors, such as disease,
parasitism, predation, and competition, and due to density independent factors, like the weather. As I was driving my tractor through the smoky haze blanketing my farm while disking fire lanes, I pondered, “What is the primary factor causing the perceived bust in the exotic snail populations? What if it is not subtle in this case but so obvious that it is hidden in plain sight?” Then, it hit me – – the exceptional drought plaguing the Southern U.S. has temporarily stemmed the proliferation of exotic Pomacea and spawned official complacency. It makes sense because current “exceptional drought” map of the U.S. generously overlaps the range of P. insularum.

While flooding is documented to assist the range expansion of exotic Pomacea, if not the eggs, one can logically conclude that extreme drought should be detrimental. To test my hypothesis, I took a walk around Wellman Pond, the test site for our apple snail traps and my favorite place to observe Pomacea insularum. I had not visited the site for months, and while I expected some impact of the recent drought, I was amazed to see the lowest water level ever. As I walked on the dry lake bottom within the periphery of emersed vegetation, I saw numerous dead snails, stranded egg clusters, and an army of foraging fire ants (See “Rematch: Pomacea versus the Red Fire Ant”). Clearly, the exotic Pomacea have had a difficult spring season in 2011 at Wellman Pond . . . and likely elsewhere in the South.

The image above is typical of the entire shoreline of Wellman Pond. Fire Ants are devouring most of the snail eggs, while the adult snails have lost access to the refuge from predation and egg laying substrate provided by the emersed vegetation. These hard times for exotic apple snails will surely end on Wellman Pond and elsewhere in the southern United States. The current rainfall deficit will inevitably swing the other way. In some future wet period, the expansion of the exotic Pomacea will likely resume with a vengeance. The snails are more vulnerable to control efforts now than ever. This is no time for official complacency based on the false hope of the boom-and-bust model. Posted by Jess Van Dyke

Pomacea’s Incredible, Indigestible Eggs

I have often wondered why the eggs of Pomacea canaliculata and P. insularum are not quickly devoured by any number of predators. The pink clusters draped on emergent plant stems around lakes could not be more obvious. However, these numerous clumps of protein and carbohydrates go largely untouched aside from occasional attacks by red fire ants, Solenopsis invicta (see post entitled, “Rematch: Pomacea versus Red Fire Ant”). Finally, a fascinating answer to this mystery has been provided by the outstanding team of Professors Dreon, Ituarte, and Heras of the National University of La Plata in Argentina.

Throughout the natural world, undefended eggs provide easy, nutritious meals. It is common for half of them to be lost to predation. Most animals rely on either hiding their vulnerable ova, guarding them, or producing so many eggs that a future generation is assured. No doubt Pomacea are prodigious breeders, but they also employ “aposematism,” a common characteristic of dangerous prey. Using warning signals, such as color, sound, or odors, certain prey clearly advertize that it is unwise to attack them. Such warnings are beneficial to both predator and prey. Certainly, the blatant display of bright-pink eggs by exotic Pomacea is the form of aposematism, called “warning coloration,” but what could possibly be danger in eating them?

Endowing eggs with chemical defenses in not uncommon in invertebrates, and Dreon, Heras, et al., (2008) already established that Pomacea canaliculata eggs contained such a predator repellant. The authors found that a rare protein neurotoxin was produced by albumen secretory cells in developing Pomacea canaliculata eggs. Further, they demonstrated that injections of this neurotoxin, called Perivitellin-2 or PV2, had lethal effects on rodents (LD50, 96 h @ 2.3 mg/kg) primarily because of damage to their spinal cords. However, this neurotoxin was fragile (heat sensitive), however, and there was evidence of antibody response to sublethal doses. The presence of PV2 did not seem enough to dissuade almost all predators from consuming Pomacea eggs suggesting some complementary defensive mechanism.

The rest of the story is provided in a publication this month by the same team (see Dreon, Ituarte, and Heras (2010) in Recent Publications). It is hard to imagine eggs that are not highly nutritious, and developing apple snail ova are “filled with large amounts of polysaccharides and proteins,” as the authors put it. However, there is another surprise for predators in the perivitellin fluid that surrounds the fertilized Pomacea oocyte, besides PV2. The same brightly-colored, caratenoid  protein, called ovorubin, that warns away predators and blocks damaging solar radiation is also a proteinase inhibitor. Feeding trials revealed that rats fed ovorubin lost weight because it binds to trypsin, a common digestive enzyme that breaks down proteins.

In an elegant defense of her young, the female snail not only adds a neurotoxin to the perivitellin fluid, but for good measure, colors it bright-pink with a compound that impedes digestion of protein. “This [protease inhibitor] role has not been reported in the animal kingdom, but it is similar to plant defenses against herbivory,” state the authors. Only red fire ants are determined enough to ignore the apple snail’s clear warning. A common TV advertisement trumpets that chicken ova are “incredible, edible eggs.” Well, the apple snail’s brightly-colored advertisement to predators is: “These are my incredible, indigestible eggs!” Posted by Jess Van Dyke

[Note: I started this weblog two years ago. Subsequently, there have been 24,000 hits from all over the world. I am grateful to all my old and new friends. Thanks for your help and encouragement!]


About Snail Busters

The Snail Busters Blog was created to facilitate communication between aquatic resource managers who are fighting the spread of invasive, South American apple snails, specifically Pomacea maculata (formerly P. insularum) and P. canaliculata, in the U.S.

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

Join 21 other followers


Follow

Get every new post delivered to your Inbox.