Pomacea maculata

Invasion History

First Non-native North American Tidal Record: 1996
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1996

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General Invasion History:

Pomacea maculata is native to South America from Uruguay, Paraguay, and the bordering areas of Brazil and Argentina, north to the Amazon River (Rawlings et al. 2007; Hayes et al. 2012). It was initially identified as the very similar P. canaliculata (Thompson 1997), also widely introduced around the world. Genetic studies indicated that in North America, P. canaliculata is only established in California and Arizona, and that apple snails established in Florida, Texas, Georgia, Alabama and Louisiana, were P. maculata (=P. insularum) (Rawlings et al. 2007; Hayes et al. 2012).

Pomacea maculata was probably introduced by the aquarium industry, and was first collected at a pond in Lantana, Florida (FL) in 1987 (Thompson 1997, USGS Nonindigenous Aquatic Species Program 2009). This snail's bright colors and large size attracts aquarists, but its appetite for aquarium plants may lead to frequent releases (Cowie and Hayes 2012). It has become widespread in freshwater ponds, swamps, and canals from South Carolina and Georgia to Florida and the Everglades (Rawlings et al. 2007; USGS Nonindigenous Aquatic Species Program 2009; Byers et al. 2013). It may occur in tidal fresh wetlands on the East Coast of Florida, but we do not have definite records from these habitats. It is established in tidal freshwater wetlands on the Gulf Coast from Tampa Bay, FL to Galveston Bay, Texas (TX) (Kyle et al. 2011; Martin et al. 2012; USGS Nonindigenous Aquatic Species Program 2013). This snail has an upper salinity tolerance of about 7 PSU and a lower temperature tolerance of 15°C, which will limit its distribution in the US (Ramakrishnan 2007). Byers et al. (2013) found that this species has occupied most of its potential range, based on current climate conditions, and that low pH would limit its occurrence in acidic wetland regions.

North American Invasion History:

Invasion History on the Gulf Coast:

Pomacea maculata was found in a tidal canal in Tampa, Florida (FL) in 1996, and is widespread in Tampa River tributaries (Florida Fish and Wildlife Commission 2006; USGS Nonindigenous Aquatic Species Program 2013). In 2000, it was found in Mustang Bayou and the American Canal, in the suburbs around Houston, Texas (TX). In 2003, an established population was found in Langan Park, Mobile, Alabama, and by 2009 it had spread to within a mile of the Mobile-Tensaw Delta, at the head of Mobile Bay (Martin et al. 2012). In 2007, one population had reached tidal waters of Galveston Bay, at Horsepen Bayou, TX (Kyle et al. 2009). In coastal Louisiana, in 2006-2009, this snail was found to be established in the Verrett Canal, in Gretna, near New Orleans, and in swamps in Terrebonne Parish (USGS Nonindigenous Aquatic Species Program 2009).

Invasion History Elsewhere in the World:

Pomacea spp. (then presumed to be all P. canaliculata) were illegally introduced from Argentina to Taiwan around 1980, as a food animal, and then, with multiple introductions from 1981 to 1982 became widespread in Asia, from southern China, Korea, and Japan to Indonesia (Hayes et al. 2008; Cowie and Hayes 2012). Most of the populations were P. canaliculata, but P. maculata were genetically identified in South Korea, Vietnam, Cambodia, Thailand, and Malaysia (Hayes et al. 2008). In 2009, P. maculata was detected in rice fields and irrigation channels in the Ebro Delta, Spain, the first 'wild' occurrence in Europe. Occurrences in Europe are probably due to the aquarium trade, although importation with rice shipments is also a possibility (Ministry of Environment, Rural and Maritime 2011). Currently P. maculata is known from 13 countries (Cowie et al. 2017).

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Description

Pomacea maculata has a relatively thick, dextrally coiled and globose shell with a low spire. The shell is smooth, with fine growth lines and occasional growth arrests. The adult shell has 4-5 whorls, separated by a deep suture. The shell opening is large and oval to round, with a reflected edge. The upper shoulder of the aperture is curved, and projects out at an angle of less than 90 degrees, in contrast to a right angle in P. diffusa. The umbilicus is narrow, but deep. The operculum is large and horn-colored. Adult shells range from 35 to 165 mm, and are highly variable in color, ranging from yellow to yellow-brown, frequently with a dark banding pattern. The body is grey-brownish with dark spots. The egg masses are pink, and deposited up to 1 m above water level on hard surfaces or vegetation. Description from: Thompson 2004, Howells et al. 2006, Rawlings et al. 2007, Hayes et al. 2012, and Ghesquiere 2013.

Pomacea maculata (=P. insularum) and the unidentified species formerly known as P. haustrum and P. canaliculata belong to a species complex of South American apple snails, which have been widely introduced in warmer parts of North America and Asia. The three species have only small differences in shell morphology, but their egg masses are more distinct in color and shape. Molecular identification has been important in clarifying the identity and origin of these snails (Rawlings et al. 2007; Hayes et al. 2008; Hayes et al. 2012; Cowie and Hayes 2012). The egg masses of P. maculata average about 1500 eggs, but can contain up to 25000 eggs, smaller than those of P. maculata The eggs are ~2 mm in diameter (Hayes et al. 2012).

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Taxonomy

Ecology

General:

Pomacea maculata has separate sexes and females tend to be larger than males. Fertilization is internal and eggs are laid in masses, out of the water, up to 1 m above the water line on rocks or vegetation (Cowie and Hayes 2012). In coastal Texas, eggs were laid from March to November, and snails born in spring could reach maturity (~35 mm) in 4 months (Burlakova et al. 2010). In experiments, P. maculata females preferred round poles to flat structures and an exotic Asian plant, Taro (Colocasia esculenta) to a native plant, Pickerelweed (Pontedaria cordata) (Kyle et al. 2011). Females lay about one clutch per week, averaging 2064 eggs per clutch. The egg masses are bright pink and are easily visible. Eggs take about 2 weeks to hatch, varying with temperature, with the young snails falling into the water. Out-of-water egg deposition is probably an adaptation to stagnant tropical waters (Cowie and Hayes 2012). Immersion reduces hatching success by 75%, while predation on submerged eggs reduced hatching by 99% (Horn et al. 2008).

Pomacea maculata is limited to fresh and oligohaline waters in warm-temperate to tropical climates. The lower temperature limit for long-term survival is 15°C, but it can tolerate lower temperatures for shorter time periods, eg. 55% survival at 5 days at 5°C (Ramakrishnan 2007; Matsukura et al. 2016). The upper experimental salinity limit was 6.9 PSU (Ramakrishnan 2008), but we have not found records from saline waters, so far. Apple Snails are obligate air-breathers and have a pulmonary sac as well as a gill, and are amphibious in their habits (Cowie and Hayes 2012). The Spotted Apple Snail can tolerate 33-300 days of air exposure, depending on temperature and humidity (Ramakrishnan 2007; Glasheen et al. 2017). This could facilitate overland transport with crops or other cargo.

Pomacea maculata grazes on emergent aquatic plants, terrestrial plants adjacent to the water, and submerged plants. Pomacea maculata and P. canaliculata are believed to have similar diets and are documented to feed on more than 40 species of plants (Carlsson et al. 2004; Morrison and Hay 2011; Burks et al. 2011; Kyle et al. 2011; Ministry of Environment, Rural and Maritime 2011). These include exotic aquatic plants from South America and elsewhere (e.g. Alligatorweed- Alternanthera philoxeroides; Water Hyacinth- Eichhornia crassipes; Eurasian Watermilfoil- Myriophyllum spicatum, etc., Hydrilla verticillata), native North American aquatic plants (e.g. Waterlily- Nymphaea odorata; Bladderwort- Utricularia spp.; Pickerelweed- Pontederia cordata, Vallisneria americana), and crops such as Lettuce (Lactuca sativa) and Rice (Oryza sativa) (Gettys et al. 2008; Morrison and Hay 2011; Burks et al. 2011; Kyle et al. 2011; Ministry of Environment, Rural and Maritime 2011). Pomacea maculata fed and grew most actively in fresh water, on freshwater plants (Alternanthera philoxeroides or Sagittaria lancifolia), and showed minimal activity and feeding on brackish-water plants (Typha angustifolia and Scirpus validus) at 5 PSU (Low and Anderson 2017). Feeding was greatest between 20 to 30 C, and was reduced at 15 and 35 C (Gettys et al. 2008).

Food:

Submerged vegetation, emergent vegetation

Consumers:

birds, fishes, mammals, humans

Competitors:

Other Ampullarid snails

Trophic Status:

Herbivore

Herb

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Habitats

General Habitat	Grass Bed	None
General Habitat	Terrestrial	None
General Habitat	Canals	None
General Habitat	Tidal Fresh Marsh	None
General Habitat	Nontidal Freshwater	None
General Habitat	Swamp	None
General Habitat	Coarse Woody Debris	None
General Habitat	Fresh (nontidal) Marsh	None
Salinity Range	Limnetic	0-0.5 PSU
Salinity Range	Oligohaline	0.5-5 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None
Tidal Range	Mid Intertidal	None
Tidal Range	High Intertidal	None
Tidal Range	Supratidal	None
Tidal Range	Emergent	None
Vertical Habitat	Epibenthic	None

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	15	Experimental (Ramakrishnan 2007). Pomacea maculata can tolerate short exposures to lower temperatures (0-5 °C) for 2-5 days (Ramakrishnan 2007; Matsukura et al. 2015).
Maximum Temperature (ºC)	37	Experimental (Ramakrishnan 2007); 50% survival for 10 days at 7 C
Minimum Salinity (‰)	0	This is a freshwater species.
Maximum Salinity (‰)	10	Experimental (Ramakrishnan 2007, 7 PSU; Martin and Valentine 2012, Bernatis et al., 8 PSU, Martin et al. 2014, 10 PSU, survival with some growth for 2 weeks)
Minimum pH	4	Ramakrishnan 2007
Maximum pH	10	Ramakrishnan 2007
Minimum Reproductive Salinity	0	This is a freshwater species.
Maximum Reproductive Salinity	10	Egg masses hatched and developed at 10 PSU, though with reduced growth rates (Martin and Valentine 2014). Hatchlings in South Carolina survived well at 4 PSU, but had 17% survuval at 8 PSU wa 18% (Underwood et al. 2019).
Minimum Length (mm)	35	Minimum adult length (Hayes et al. 2012)
Maximum Length (mm)	165	Maximum adult length (Hayes et al. 2012)
Broad Temperature Range	None	Subtropical-Tropical
Broad Salinity Range	None	Nontidal Limnetic-Oligohaline

General Impacts

Pomacea maculata and P. canaliculata (Channelled Applesnail) have had a wide range of ecological and economic impacts. Their large size and varied colors and markings make them attractive aquarium pets (Ghesquiere 2013). They were shipped to Asia, in an unsuccessful attempt to introduce them as food and soon became serious agricultural pests in rice fields (Carlsson et al. 2004; Cowie and Hayes 2011; Ministry of Environment, Rural and Maritime 2011). In the southern US, they are regarded as potentially serious agricultural and ecological pests. Possible ecological impacts include extensive herbivory in wetlands, effects on wetland water quality, and in Florida, competition with the native Florida Apple Snail (P. paludosa) and interference with the native snails' specialized avian predator, the Snail Kite (Rostrhamus sociabilis) (Carlsson et al. 2004; Darby et al. 2007; Morrison and Hay 2010; Martin et al. 2012; Posch et al. 2013). So far, the extent of actual impacts in Gulf Coast estuaries is unclear.

Economic Impacts

Agriculture: Pomacea maculata is regarded in Asia as one of the most damaging pests in irrigated rice culture. Pesticides are extensively and often illegally used to control snails in rice fields. It is also a pest of cultivated Taro (Colocasia esculenta) in Hawaii (Cowie and Hays 2011). In coastal rice-growing areas of Texas, snails reproduce much more rapidly and reach much higher densities, than in stable pond environments (Burlakova et al. 2010). However, we do not have data on economic losses due to Applesnails in Texas or elsewhere in the US.

A control attempt in the Ebro Delta, Spain, in November 2013, involves flooding irrigation channels with saltwater. Volunteers rescued native mussels and snails, before the flooding, and after saltwater flooding, the area will be flooded with freshwater again. The activity was coordinated by Delta del Ebro Natural Park and involved the government of Catalonia, the irrigation community, Forestal Catalana, and SEO/BirdLife (posted on Aliens-L listserve, 11/13/2013).

Ecological Impacts

Herbivory: Pomacea maculata feeds on a wide range of aquatic and riparian plants, including native and introduced invasive plants. Experiments and field studies in Thailand indicate that Apple Snails (P. canaliculata) at high densities can eliminate aquatic plants, resulting in domination of water by phytoplankton (Carlsson et al. 2004). In experiments in Florida, P. maculata and P. canaliculata both consumed some native plants (Bladderwort, Utricularia sp. and Blue Water Hyssop, Bacopa caroliniana) at higher rates than the native P. paludosa (Morrison and Hay 2010). In experiments, the Spotted Applesnail grew rapidly on three invasive plants that had been considered less palatable (Eurasian Watermilfoil- Myriophyllum spicatum; Wild Taro- Colocasia esculenta; Water Hyacinth- Eichhornia crassipes; Burks et al. 2011).

Habitat Change: Experiments and observations of Apple Snails (P. canaliculata) in Thailand can alter water quality and nutrient cycling in wetlands by eliminating macrophytes, leading to dominance by phytoplankton, increased turbidity, and elevated concentrations of nitrogen and phosphorus (Carlsson et al. 2004). In coastal wetlands, potential impacts include loss of habitat for ecologically and economically important fish and invertebrate species, loss of protection against erosion, and loss of aesthetic qualities (Gossett et al. 2004; Martin et al. 2012). Control of P. maculata populations was attempted in the Mobile-Tensaw Delta, Alabama, in 2009, motivated by concerns for habitat quality of the wetlands, using several doses of copper sulfate in the water, releases of snail-eating Redear Sunfish (Lepomis microlophus), and hand-picking of snails and their egg-masses. These efforts reduced the population, but did not eliminate all the snails. The population recovered rapidly, leading the authors to stress prevention as the best form of control (Martin et al. 2012).

Competition: Field observations and experiments indicate that P. maculata appears to compete with the Florida Apple Snail (P. paludosa), replacing the native in Florida lakes and wetlands (Darby et al. 2007; Posch et al. 2013). In rearing experiments, juvenile P. paludosa had a reduced growth rate in the presence of P. maculata, but the mechanism of competition was not clear (Posch et al. 2013).

Food/Prey: Adult Pomacea maculata are larger than any of the native freshwater snails in Florida and pose a challenge to snail-eating predators, though juveniles can be eaten by fish, ducks, etc. (Cowie and Hayes 2012). The Snail Kite (Rostrhamus sociabilis) is a raptorial bird, with an endangered population in southern Florida, which specializes in preying on the native Florida Apple Snail (P. paludosa). The Spotted Applesnail has partially replaced the native snail in many Florida lakes and wetlands, and its larger size has posed some difficulties for the Kite, resulting in frequent dropping of snails and longer time spent feeding. These problems are greatest for juvenile birds. They might be offset by the higher meat content of the exotic snail, but further study is required (Darby et al. 2007).

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