The fragile cockle Fulvia fragilis (Forsskål, 1775) is a cardiid bivalve presumably native to coastal waters in the Indian Ocean, known from the Persian Gulf to the southeastern African coast and from a single population located along the central-western African coast (Vidal 1994, Cosel 1995, Angelidis 2013, Gvozdenović et al. 2019, Rizgalla et al. 2019). In recent times, human activity has led to the spread of F. fragilis to additional areas and mostly to the Mediterranean Sea, becoming first established in the eastern part of it and then gradually expanding to its westernmost parts (Angelidis 2013, Crocetta et al. 2013, Forner i Valls 2018, Gvozdenović et al. 2019, Rizgalla et al. 2019). Its expansion into the Mediterranean Sea seemed to be influenced both by Lessepsian migration through the Suez Canal, supported by its initial reports coming from inside the canal (Moazzo 1939, Rizgalla et al. 2019), and further dispersal through ship ballast water, as evidenced by its frequent occurrence in and around ports (Zenetos et al. 2004, Goud & Mifsud 2009, Rizgalla et al. 2019). Despite its increasing distribution, F. fragilis had not yet been reported in Brazil by previous assessments of its bivalve fauna (Passos et al. 2024).

From May to July 2025, numerous shells identified as Fulvia fragilis were found washed up on Barequeçaba beach in São Sebastião, São Paulo state, southeastern Brazil (23°49'39.432"S, 45°26'09.204"W). A sample of 11 shells was collected for analysis (Figs 1–4). In July 2025, an additional shell was found at Segredo beach (23°49'40.728"S, 45°25'23.192"W), which is located within the Center for Marine Biology of the University of São Paulo (CEBIMar/USP) and relatively near Barequeçaba (circa 1 km), indicating the presence of F. fragilis in that area as well. The specimens appeared recently dead as their shells were intact and showed no signs of erosion (Figs 1–4). Following the discovery of the shells, efforts were made to find live F. fragilis specimens in the intertidal and shallow subtidal zones of both Barequeçaba and Segredo beaches, but these attempts were unsuccessful, and no further dead shells were found in subsequent months. The species was identified as Fulvia fragilis based on its morphology following the description by Reeve (1843). Diagnostic characters included an obliquely ovate outline, very delicate and papyraceous thickness, smooth radial ribs, and a color pattern that is white with irregular orange stripes externally and a purple posterior margin internally. All collected shells were deposited in the Mollusca collection at the Museum of Zoology of the University of São Paulo (MZSP; São Paulo, Brazil) under the lot number MZSP 171368. A survey on the iNaturalist citizen science platform has revealed one additional record of Fulvia fragilis from Vitória, Espírito Santo state (20°18'13.3"S, 40°17'25.0"W), dating from March 2024, which shows the external view of an empty shell washed ashore (Reis 2024).

Figs 1–4

Shells of Fulvia fragilis collected in Barequeçaba beach, São Sebastião, São Paulo state, Brazil (MZSP 171368): 1 – specimen #1, external view; 2 – same, internal view; 3 – specimen #2, external view; 4 – same, internal view. Scale bar 10 mm

The species was not reported by previous surveys at São Sebastião (e.g., Migotto et al. 1993, Tallarico et al. 2014, Amaral et al. 2024), suggesting a recent introduction. As São Sebastião has a large port, ship ballast water is the likely vector for the introduction of F. fragilis in Brazil too. However, it is currently unknown if a population of F. fragilis has formed in São Sebastião and whether the specimens found originated from native populations in the Indian Ocean and West Africa or from the non-native populations in the Mediterranean Sea. On the other hand, the record found on iNaturalist, which may be the earliest record of F. fragilis in Brazil, was likely from an independent introduction since Vitória is also home to a large port and quite distant from São Sebastião (circa 740 km; Fig. 5). This finding further highlights the potential of social media platforms and citizen science to track biological invasions, as previously reported for various other non-native molluscs in Brazil (Rosa et al. 2022, 2025, Akira-Umeno et al. 2025, Barbieri et al. 2025).

Fig. 5

Localities with records of Fulvia fragilis in Brazil. Records from São Sebastião (SP) refer to the specimens studied herein, while the record from Vitória (ES) is sourced from iNaturalist (https://www.inaturalist.org/observations/201964471). State abbreviations: BA – Bahia; DF – Distrito Federal; ES – Espírito Santo; GO – Goiás; MG – Minas Gerais; MS – Mato Grosso do Sul; MT – Mato Grosso; PR – Paraná; RJ – Rio de Janeiro; RS – Rio Grande do Sul; SC – Santa Catarina; SP – São Paulo

Despite the currently widespread distribution of F. fragilis across the world, information about its biology and potential ecological impacts in newly invaded areas is scarce (Rizgalla et al. 2019), with the sole exception that it is a simultaneous hermaphroditic species, known to spawn continuously throughout the year, which likely contributes to its ability to quickly establish populations in new areas where it is introduced (Rifi et al. 2011).

Since F. fragilis appears to have reached the Brazilian coast recently, it is still uncertain whether it will form established populations and have any impacts on local ecosystems. This report of yet another introduced species highlights the need for further monitoring of non-native molluscs in Brazil, as the country has been increasingly affected by biological invasions in recent years (Carranza et al. 2023, Machado et al. 2023, Darrigran et al. 2025).