Physella acuta (Draparnaud, 1805)

Régis-Silva, Caio Correia, Rosa, Leonardo Cruz da & Dornellas, Ana Paula Siqueira, 2025, The most cosmopolitan freshwater gastropod invades the Lower São Francisco River: first record of Physella acuta in Sergipe, Biota Colombiana 26 (1), pp. 1-8 : 4-5

The 17 collected specimens display shell features consistent with those of

Physella acuta :

a sinistral thin shell with longitudinal striations, oval shape, moderately lustrous, short-pointed spire, and a large ear-shaped aperture. The shells of live organisms had an external coloration ranging from dark brown to beige ( Figure 2 and Figure 3 ). In the laboratory, the empty shells are opaque with coloration ranging from beige to cream on both outer and inner surfaces ( Figure 4 ). The shell height ranged from 2.6 to 6.3 mm, mean = 5.14± 0.23 mm ( Figure 4 ). This interval (4- 6 mm) was the most frequently encountered by Paul & Aditya (2021) and Miyahira et al. (2023), and it allows to estimate that the specimens were approximately 30 weeks old ( Nuñez, 2010).

These specimens confirm the first record of Physella acuta in Sergipe, in the Lower São Francisco River, thus filling a gap in the understanding of its distribution in Brazil ( Table 1 ; Figure 5 ). The record represents a new addition to the growing list of invasive freshwater mollusks in the São Francisco River basin, such as Melanoides tuberculata ( Souto et al., 2011) , Corbicula fluminea (O. F. Müller, 1774) ( Santana et al., 2013) , Limnoperna fortunei (Dunker, 1857) ( Barbosa et al., 2016) , and C. largillierti (Philippi, 1844) ( Rosa, 2023) . The unintentional introductions of P. acuta individuals and eggs are attributed to aquarium-related activities, especially through the transport of aquatic plants ( Dillon et al., 2002; Miyahira et al., 2010; Latini et al., 2016; Vinarski, 2017; Ng et al., 2018; NIWA, 2020; Miyahira et al., 2023). P. acuta exhibits exceptional tolerance to water pollution ( Brackenbury & Appleton, 1991; Appleton, 2003; Collado et al., 2020; Paul & Aditya, 2021), facilitating its proliferation within disturbed habitats. This tolerance potentially fosters a link between the species distribution and anthropogenic activities associated with pollution ( Appleton, 2003; Wethington, 2004; Paul & Aditya, 2021).

Physella acuta has a high degree of habitat plasticity, including artificial ones, such as sewage drains ( Appleton, 2003; Paul & Aditya, 2021), controlled aquatic environments ( Alexandre, 2017), areas around major urban centers (particularly ports) ( Appleton, 2003; Miyahira et al., 2010), reservoirs ( Coelho et al., 2024; Miyahira et al., 2020), dams ( Kock & Wolmarans, 2007; Latini et al., 2016; Miyahira et al., 2020), artificial lakes ( Leme, 1966; Paraense & Pointier, 2003), channels and ditches ( Kock & Wolmarans, 2007; Moratelli et al., 2023), small tanks ( Latini et al., 2016), concrete pots and ponds with ornamental aquatic plants ( Kock & Wolmarans, 2007), ornamental ponds ( Appleton 2003; Ng et al. 2018), irrigation furrows ( Kock & Wolmarans, 2007), paddy fields ( Ng et al. 2018), pans ( Kock & Wolmarans, 2007), quarries ( Kock & Wolmarans, 2007), and as hitchhikers on aquatic plants being sold in ornamental pet trade shops ( Ng et al. 2018). In natural environments, the species occurs in springs ( Kock & Wolmarans,2007), estuaries ( Ng et al., 2018), wetlands (NIWA, 2020), swamps ( Kock & Wolmarans, 2007), bogs ( Paul & Aditya, 2021), rivers ( Appleton, 2003; Taylor, 2003; Lydeard et al., 2016; Kock & Wolmarans, 2007; Lydeard et al., 2016; Thiengo et al., 2017; Ng et al., 2018; Collado et al., 2020), streams ( Appleton, 2003; Latini et al., 2016; Lydeard et al., 2016) (including insular ones) ( Miyahira et al. 2010; Miyahira et al., 2023), Vlei (shallow, usually seasonal or intermittent bodies of water, typically found in South Africa) ( Kock & Wolmarans, 2007), lakes ( Latini et al., 2016; Collado et al., 2020; NIWA, 2020), ponds ( Appleton, 2003; Kock & Wolmarans, 2007; Lydeard et al., 2016; Paul & Aditya, 2021; NIWA, 2020), waterholes ( Kock & Wolmarans, 2007), on rocks and sandy substratum ( Appleton, 2003), roots of floating water hyacinths ( Kock & Wolmarans, 2007), on macrophytes (Dillon Junior, 2000; Miyahira et al., 2023), and attached to other marginal aquatic vegetation, stones, and leaf litter ( Miyahira et al., 2023).

The success of Physella acuta as an invasive species might be attributed partially to its adaptability to diverse environmental conditions. This species exhibits high tolerance and resilience to fluctuations in rainfall, water body levels ( Brackenbury & Appleton, 1991; Gulanicz et al., 2018; Miyahira et al., 2023), varying current velocities ( Appleton, 2003), and salinity ( Dunlop et al., 2008; Zukowski & Walker, 2009). Interestingly, despite its tolerance to fluctuations, P. acuta populations appear negatively impacted by increased rainfall volume, especially in anthropic water bodies lacking marginal vegetation ( Miyahira et al., 2023). Its tolerance for strong current speeds and apparent indifference to marginal vegetation allow P. acuta access to a wider range of suitable substrata compared to native snail species ( Appleton, 2003). For P. acuta adults, experiments on instantaneous salinity tolerance (72 h and lethal dose for 50% of the sample) demonstrate a high tolerance, with a> 5.2-11.8 gL-1 limit ( Dunlop et al., 2008; Zukowski & Walker, 2009).

Previous studies have documented the detrimental effects of Physella acuta on native communities across diverse ecosystems ( Brackenbury & Appleton, 1991; Zukowski & Walker, 2009; Nuñez, 2010). Compared to many native snails, P. acuta exhibits high fecundity and shorter egg hatching times, features that grant it a competitive advantage for establishing populations ( Zukowski & Walker, 2009; Núñez, 2011). As a microphagous feeder, it competes with native grazers like other snails and insects for shared food sources such as detritus and algae. Moreover, its ability to reach high densities in new habitats ( Zukowski & Walker, 2009; Núñez, 2010; Vinarski, 2017) raises concerns about potential food resource depletion for native competitors ( Appleton, 2003). Potential physical interactions between P. acuta and native invertebrates in high-density situations could further magnify its negative impacts ( Appleton, 2003; Zukowski & Walker, 2009; Nuñez, 2010). Finally, the species has medical significance, as it serves as an intermediate host for human trematodes such as Fasciola hepatica L., 1758 ( Barros et al., 2002) and Echinostoma Rudolphi, 1809 (Zimmerman et al., 2014).

The record of Physella acuta in the Lower São Francisco River expands our knowledge of its distribution and emphasizes the importance of continuous monitoring programs to ensure early detection and prompt management interventions to mitigate potential ecological and health risks. Controlling the aquarium trade and associated goods remains critical to prevent freshwater snail invasions. These vectors are well-established pathways for the introduction of invasive species into ecosystems. Despite uncertainty around its full ecological impact, addressing key questions about its distribution, abundance, potential health risks, and effects on native species is crucial. Future research involving additional sampling is necessary to map the distribution pattern of P. acuta throughout the Lower São Francisco River. This information will help understand interactions with both native and invasive species and determine their impacts on local environments.

Figures

Figure 2. Collection sites of Physella acuta (Draparnaud, 1805) in the reservoir of the Xingó Hydroelectric Power Plant.

Figure 3. Live specimens of Physella acuta (Draparnaud, 1805).

Figure 4. Shells of Physella acuta (Draparnaud, 1805).

Figure 5. Updated map of Physella acuta (Draparnaud, 1805) distribution in Brazil.