Lysmata rauli is native to the Indo-Pacific and introduced in its type locality (Brazil) and the Atlantic as a whole

At present, determining the natural distribution of L. rauli is confounded by the discovery of a phylogenetically close and currently undescribed species (L. sp. AUS2) collected from north Australia, which is morphologically similar (albeit with some differences in the number of carpal and meral second pereopod segments) and likely possesses a similar coloration pattern (thin red stripes with dark transverse bands on the pleon). Although we do not know the coloration pattern of the Australian individuals included in the present study, photographs of Australian “ L. vittata ” (Vaughan et al. 2018a; Barton et al. 2020) are similar to photographs/illustrations of L. rauli from Brazil (Laubenheimer & Rhyne 2010; Soledade et al. 2013; Almeida et al. 2018; Alves et al. 2018, 2019), as well as individuals cited as “ L. vittata ” from Panama (Pachelle et al. 2018), Singapore (Anker & De Grave 2016), and the Mediterranean (Abdelsalam 2018). Additionally, both species are likely to tolerate tropical conditions and could overlap in large portions of the Indo-Pacific. Thus, given that L. vittata is likely restricted to the temperate/subtropical waters of the northern Indo-Pacific and New Zealand, it is difficult to reclassify historic reports of “ L. vittata ” from the tropical Indo-Pacific as either L. rauli or L. sp. AUS2. However, natural biogeographic barriers in the region, such as the Sunda Shelf can affect gene flow and aid speciation events (Briggs & Bowen 2013; Bowen et al. 2016) and may provide insight into the biogeography of L. rauli and L. sp. AUS2. A directed sampling effort throughout the wider Indo-Pacific is required to determine the distribution of both species and others once confused with L. vittata in the region.

Our analyses confirm the occurrence of L. rauli in Panama, Brazil, Thailand, and Hong Kong. We posit that L. rauli is native to the subtropical and tropical Indo-Pacific and introduced in the western Atlantic, including the type locality, Salvador, northeastern Brazil. The phylogenetic and geographic affinity between L. rauli and other species that naturally occur in the Indo-Pacific suggests L. rauli is native to this region. We observed in our phylogeny that L. rauli comprised a monophyletic lineage with L. sp. AUS2 and L. sp. CHINA, two species from the Indo-Pacific (fig. 4). This clade was sister to a clade that included four other species from the Indo-Pacific (L. vittata, L. sp. AUS1, L. dispar, and L. lipkei).

Similar to L. vittata in the western Atlantic, we assume ballast water was the introduction vector for L. rauli in Brazil. To date, L. rauli has been reported along a large swath of Brazilian coastline, from Ilha de Anhatomirim in the south to the Vaza-Barris estuary in the north (Alves et al. 2018; Pachelle et al. 2018, 2020; Santos et al. 2021). It is uncertain if the Panamanian populations resulted from separate introduction events or if shrimp moved northward naturally from Brazil. Pachelle et al. (2018) surmised the introduction of L. rauli (cited as L. vittata) in the Western Atlantic resulted from a recent and very quick invasion. Reinforcing this hypothesis are the introductions of other Asian decapod crustaceans within Brazil, including another lysmatid shrimp, L. lipkei (Pachelle et al. 2016; Alves et al. 2018), the alpheid shrimp Athanas dimorphus Ortmann 1894, and the swimming crab Charybdis helleri A. Milne-Edwards 1867 (Pachelle et al. 2011; Almeida et al. 2012). Given the documented occurrence of L. rauli in Hong Kong and Thailand, indicating a tolerance of tropical and subtropical conditions, we surmise this species has the potential to spread further northward along the South and Central American coast and the Caribbean and possibly Gulf of Mexico, as well as further south as cooling waters allow.