First record of the non-native medusa Blackfordia virginica (Hydrozoa, Leptomedusae) on the coast of Uruguay, Southwestern Atlantic

Editor: Rubens M. Lopes Marine invasions are a growing threat challenging the preservation of ocean biodiversity. These invasions occur in a context of global change due to increasing anthropogenic activities, with maritime transport being the main mechanism of introduction of aquatic invertebrates (Grigorovich et al., 2003). Shipping serves as a vector for the dispersal of organisms through ballast water, sediment, or hull fouling (Minchin & Gollash, 2002). Aquaculture and aquarium trade are also vectors of transfer and introduction of alien species (Minchin, 2007; Grosholz et al., 2015). Among marine species, hydrozoans are considered successful invaders due to their environmental flexibility, small size, wide variety of life cycles, and reproductive processes that allow them to be easily transported and to establish in new regions (Graham & Bayha, 2008; Rilov and Crooks, 2009; Folino-Rorem et al., 2008). However, due to their relatively inconspicuous and seemingly low environmental impact on ecosystems, hydrozoans may be overlooked in invasion biology (Miglietta and Lessios, 2008). Nevertheless, there are several examples of invasions by hydromedusa species in different ecosystems around the world, including the cases of Maeotias marginata, Moerisia lyonsi, Gonionemus vertens, and Blackfordia virginica, among others (Ma & Purcell, 2005, Gaynor et al., 2016, Harrison et al., 2013). Blackfordia virginica (Hydrozoa, Leptomedusae) is thought to be native to the Black and Caspian Sea and is recognized to be a successful invader of estuarine coastal waters around the world (Europe, North America, Asia, and Central America) (Bayha & Graham, 2014). In the Southwestern Atlantic, it was recorded for the first time in the northeast of Brazil (Paranaguá, 1963) and then, nearly four decades later, in the Rio de la Plata estuary on the Argentine shelf (Genzano et al., 2006) and in different estuarine ecosystems along the southern and southeastern Brazilian coast (Nogueira & Oliveira, 2006). This hydromedusa is considered an euryhaline species, which has been shown to tolerate a wide range of salinity, from 2.2 to 36 (Moore, 1987). It displays a metagenetic life cycle comprised of a benthic polyp phase, which reproduces asexually, and a planktonic sexual phase, the medusa. Pelagic medusae and benthic polyps have been observed in brackish water ecosystems, and polyps have also been found in estuaries and coastal saltwater swamps (Bardi & Marques 2009). In several tropical and temperate estuaries, B. virginica occurs seasonally, developing higher biomasses and abundances at temperatures ≥ 14 ° C (e.g. Wintzer et al., 2013; Freire et al., 2013; Jaspers et al., 2018). It feeds on adults and nauplii of copepods, barnacle nauplii (Mills & Sommer, 1995), and fish larvae (Wintzer et al., 2013). Morais et al. (2015) demonstrated that it also feed on phytoplankton and ciliates and is able to maintain a good nutritional condition during periods of low availability of metazooplanktonic prey, basing its diet on sources of particulate organic matter. © 2021 The authors. This is an open access article distributed under the terms of the Creative Commons license. Ocean and Coastal Research http://doi.org/10.1590/2675-2824069.20013vmvm Brief CommuniCation