Non-marine invasive gastropods on Ilha Grande (Angra dos Reis, Rio de Janeiro, Brazil): distribution and implications for conservation

: Invasive species are one of the main causes of biodiversity loss and the knowledge of their distribution is essential for conservation efforts. The present study inventoried the land and freshwater invasive molluscs of 25 villages of Ilha Grande (Rio de Janeiro, Brazil), an island with Atlantic Rainforest remnants. Three invasive species are found: Melanoides tuberculata (Müller, 1774), Physa acuta Draparnaud, 1805, both on two localities; and Achatina fulica Bowdich, 1822, on 16 localities. Most records were done on the island continental side, in anthropic areas, probably due to ease of access. One record was inside a conservation area, that calls concern about the spread of those species on the island and possible effects.

Physa acuta is an invasive freshwater gastropod worldwide distributed (Paraense & Pointier 2003, Taylor 2003). The first record on Brazil was in 1966, under the name Physa (Physella) cubensis Pfeiffer, 1839 (Leme 1966), but nowadays it is widespread especially in southeastern Brazil  and some records in the states of Bahia and Goiás (Santos et al. 2016). This species is hermaphrodite and recognized for some environmental impacts (Taylor 2003, Zukowski & Walker 2009.
Ilha Grande is one of the largest insular remains of the Atlantic Rainforest in Brazil, and place of four conservation areas: Ilha Grande State Park, Praia do Sul Biological Reserve, Aventureiro Marine State Park, and Tamoios Ambiental Protection Area. The first two include almost all terrestrial surface of the island, except for most villages, that are included in Tamoios Ambiental Protection Area.
Those three invasive species were already recorded for Ilha Grande: Achatina fulica was first mentioned in 2002 (Santos et al. 2002), M. tuberculata in 2005 (Santos et al. 2007), and P. acuta in 2009  to the main village of Ilha Grande, Vila do Abraão. However, the distribution of these species on the island is unknown. The main goal of this study was to present the distribution of these species on Ilha Grande, as also some observations on conservation issues, as the first step for future managing, conservation, and educational plans.

Material and Methods
Ilha Grande (23° 05', 23° 15' S and 44° 06', 44° 23' W), is an island located on the southern coast of the Rio de Janeiro state, southeast Brazil, far from 150 km from the city of Rio de Janeiro, in the municipality of Angra dos Reis. The island is covered with important remnants of Atlantic Forest especially on highlands (Callado et al. 2009), but near the coast, the habitats are modified by deforestation, non-native plants, domestic animals, and domestic sewage (Santos et al. 2007). The island can be divided into two sides, one facing the mainland (Continental or North side), with the most villages; and the other facing the open ocean (Oceanic or South side) with fewer villages and more difficult access by boats or trails.
Twenty-five localities were surveyed for invasive snails, were included the villages and nearby areas (anthropic and perianthropic). The localities were reached by trails or boats. Each locality was visited at least twice, and the search for the snails was done by three people at all kinds of suitable habitats. For A. fulica we did a visual inspection on walls, plants, under vegetation debris, and garbage for 30 minutes/ person. Melanoides tuberculata and P. acuta were searched using a handled metallic scoop in freshwater streams for 30 minutes/person. At each village were recorded the "presence" or "absence" regarding the occurrence of the target invasive species: A. fulica, M. tuberculata, and P. acuta. All collecting stations were georeferenced using a Garmin Etrex. Samples of live molluscs were placed in plastic bags or pots and took back to the laboratory for biological observations, taxonomic identification, and further parasitological studies.
Voucher specimens are housed at the Malacological Collection of the Universidade do Estado do Rio de Janeiro (UERJ).

Results
Sixteen localities of Ilha Grande present at least one invasive mollusc species: M. tuberculata, P. acuta, or A. fulica ( Figure 1 and Table 1). In most localities only A. fulica was found; in Praia Vermelha, two species were recorded (M. tuberculata and P. acuta), and on Vila do Abraão, all the three species occurs. There are only two villages with invasive species on the oceanic side (Provetá and Vila Dois Rios), and 14 on the continental side ( Figure 1 and Table 1). All the records of freshwater invasive molluscs were on the continental side, on only two villages (Vila do Abraão and Praia Vermelha). Achatina fulica has distributed along 16 (64%) villages: 14 on the continental side and two on the oceanic side. Achatina fulica was found colonizing not only the urban environments but also the surroundings of the villages in areas of secondary Atlantic Forest. The two freshwater invasive gastropods were found only at impacted water bodies, M. tuberculata in sandy bottoms, and P. acuta attached to aquatic vegetation. The two species also colonize debris and/or man-made habitats.
Most of the records were done on the borders of Ilha Grande State Park (Fig. 1), except for the occurrence of A. fulica in Vila Dois Rios that is inside the park. On Praia do Sul Biological Reserve no invasive molluscs were found.

Discussion
Achatina fulica was widespread on villages of Ilha Grande ( Figure 1 and Table 1), this is related to some features of this species like hermaphroditism, a high number of egg-laying per year (3 to 4), a high number of eggs per laying episode (200 to 400), and high adaptability to environmental conditions (Kosloski et al. 2002, Fischer & Colley 2004. This species was probably dispersed on Ilha Grande attached to plants and other goods. The distribution of A. fulica on Ilha Grande seems to be restricted to anthropic and nearby areas of secondary forest. The species was so adapted to the anthropic environment of Ilha Grande that were found at gardens, walls, and streets. Fischer et al. (2008) stated that these urban areas offer resting sites and shelters against predation. Other authors already observed these environmental preferences of A. fulica (Colley & Fischer 2009, Goldyn et al. 2017. The urban population can expand to nearby preserved forests (Raut & Baker 2002, Fischer et al. 2006, Faraco 2011. Ilha Grande has a rich and diverse fauna of land snails (Haas 1953, Santos & Monteiro 2001, Nunes & Santos 2012, Cuezzo et al. 2018), but few occur in anthropic habitat, as preferred by A. fulica. However, the expansion of this species to preserved areas can increase the negative impacts of giant African land snail on the island; although some studies do not show so drastic outputs (Miranda et al. 2015, Miranda & Pecora 2017, O'Loughlin & Green 2017. Melanoides tuberculata and P. acuta were restricted to two localities of Ilha Grande (Figure 1 and Table 1); the first record of M. tuberculata was in 2005 in Vila do Abraão (Santos et al. 2007) and P. acuta was in 2009  in the same locality. The population of M. tuberculata at Vila do Abraão was initially found in low numbers (Santos et al. 2007), therefore the population increased, also affecting negatively the native fauna (Braga et al. 2014). A subsequent record of M. tuberculata was done at Praia Vermelha ) in low numbers, probably indicating a recent introduction event, but the population still present on the following collecting events, probably indicating that population was established. This last locality is far from Vila do Abraão, therefore it is probable that this distribution extension was human-mediated (e.g. discharge of aquarium water with aquatic plants and snails). The aquatic species need more factors to be transported from one place to another, resulting in a slower dispersion, and narrow distributions on Ilha Grande. Another factor that possibly restricts the distribution of aquatic invaders is the morphology of the streams of Ilha Grande, usually small and running across small stretch before reaches the sea. Thus, these are streams with a low amount of nutrients and conductivity, preventing some newly introduced species to Most records of invasive molluscs in Ilha Grande were done on the North (or continental) side, facing the mainland. The two sides of the island present different environmental conditions (Nunes & Santos 2012) but it is probably that observed distribution is not related to those environmental factors. On the North side, there is a large number of villages, and an easier movement of goods and people, thus increasing the likelihood of an introduction. Vila do Abraão, the village with a greater flow of people on the island, was the unique place where the three invasive species were found together. The two villages on the oceanic side that presented invasive species were Provetá and Vila Dois Rios. Provetá has the second-largest resident population of the island, and Vila Dois Rios is connected by road to Vila do Abraão, one of the few roads on the island. Thus, the uncontrolled movement of people and goods seems to be important to understand and mitigate the spread of invasive molluscs on the island. This phenomenon was probably related to the explosive increase of touristic activities after the closing of Ilha Grande's Prison in 1994 (Prado 2003, Cadei et al. 2009), although a previously detailed inventory of non-marine molluscs is not available. Haas (1953) pointed out some species of land and freshwater molluscs of Ilha Grande, and at that time, no non-native species were reported.
In addition to the tourism, the villages have experienced population growth and urban expansion, this can easily be noted at Vila do Abraão, Provetá, Bananal, Matariz, and Longa. In these villages there were always new buildings that demand a continuous trade of goods with the mainland, increasing the risk of unwanted introduction of species. Moreover, Ilha Grande doesn't have any kind of sanitary barrier; villagers and tourists can bring almost all kinds of animals and plants to the island. This lack of inspection can be a highway to the introduction of non-native species. The eight villages that do not present invasive species on Ilha Grande, also do not present a great touristic flow, except for Palmas.
Most records of invasive molluscs on Ilha Grande were out of restrictive conservation areas, except for A. fulica inside the Ilha Grande State Park. This record inside the park and those on the borders of conservation areas causes concern and calls attention to the need for inspection on the goods transported to the island. Those three invaders can expand their distribution on the island if the proper conditions were offered. Another important consequence of the dispersion of invasive species is the introduction and dispersal of parasites (Font 2003). Oliveira & Santos (2019) recorded cysts of the nematode Strongyluris Müller, 1894 in the pallial system of A. fulica collected in two populations from Ilha Grande: Vila do Abraão and Vila Dois Rios. This parasite has as final host lizards or rarely anurans (Vicente et al. 1993, Bursey et al. 2003, although A. fulica can also harbor other helminths that have the man as the final common host (Thiengo et al. 2007). Some habitat of this species, like coprophagy, can make easy the establishment of new cycles (Mead 1961, Fischer 2009, Goldyn et al. 2017. Ximenes et al. (2017) reported the occurrence of Centrocestus formosanus (Nishigori, 1924) in M. tuberculata in the population from Vila do Abraão, a helminth that has birds as the final hosts.
The occurrence of A. fulica, M. tuberculata, and P. acuta represent a risk to conservation of native species and public health, an effort to control those species must be done together with environmental education, public health, and environmental authorities to prevent and mitigate the spread of these invasive species on Ilha Grande.

Author Contributions
Jaqueline L. de Oliveira: Substantial contribution in the concept and design of the study; Contribution to data collection; Contribution to data analysis and interpretation; Contribution to manuscript preparation; Contribution to critical revision, adding intelectual content.
Igor C. Miyahira: Substantial contribution in the concept and design of the study; Contribution to data collection; Contribution to data analysis and interpretation; Contribution to manuscript preparation; Contribution to critical revision, adding intelectual content.
Isabela Cristina B. Gonçalves: Contribution to data collection; Contribution to data analysis and interpretation; Contribution to manuscript preparation.
Renata F. Ximenes: Contribution to data collection; Contribution to data analysis and interpretation; Contribution to manuscript preparation.
Luiz Eduardo M. de Lacerda: Contribution to data collection; Contribution to data analysis and interpretation; Contribution to manuscript preparation.
Patrícia S. C. da Silva: Contribution to data collection; Contribution to data analysis and interpretation; Contribution to manuscript preparation.
Francielle C. Fonseca: Contribution to data collection; Contribution to data analysis and interpretation; Contribution to manuscript preparation.
Amilcar B. Barbosa: Contribution to data collection; Contribution to data analysis and interpretation; Contribution to manuscript preparation.
Gleisse Kelly M. Nunes: Contribution to data collection; Contribution to data analysis and interpretation; Contribution to manuscript preparation. Sonia B. dos Santos: Substantial contribution in the concept and design of the study; Contribution to data collection; Contribution to manuscript preparation; Contribution to critical revision, adding intelectual content.