Two new nonindigenous isopods in the Southwestern Atlantic: Simultaneous assessment of population status and shipping transport vector

The Southwestern Atlantic is often perceived as remote region, yet it is not immune to biological invasions. Patchy information on historical community composition hinders our ability to identify introductions to coastal ecosystems in this region. Hull fouling is an under-managed shipping vector that likely continues to transport large numbers of marine species worldwide. The port of Mar del Plata is a comparatively well-studied shipping and commercial hub that may serve as an observatory to monitor new introductions to the Argentine coast. Following detection of nonindigenous isopods during preliminary port sampling in 2007–2008, we organized regular port surveys aimed at assessing the level of population establishment and evaluated hull fouling as a potential introduction vector in the Port of Mar del Plata. In 2011–2012, we conducted 12 monthly dive surveys of port isopod communities in combination with three opportunistic surveys (two in-water, one in dry-dock) of hull fouling communities attached to a domestic research vessel during consecutive port calls at its base in this port. Replicate biofouling samples from underwater dock structures and the vessel's hull were collected by scraping invertebrates in 20 × 20 cm quadrats (even surfaces) and 1000 cm3 of biofouling organisms (uneven surfaces). Both in port- and hull-fouling communities, we discovered the presence of the nonindigenous isopods Dynamene edwardsi and Paracerceis sculpta. This report constitutes the first detection of these two global marine invaders in American and Argentine waters, respectively. They likely represent relatively recent introductions to this corner of the world's oceans, yet our data indicate that both species are currently well established in Mar del Plata. These results demonstrate (for the first time in the case of D. edwardsi) the potential for hull fouling to disperse both species, and raise a warning on their potential expansion to other Southwestern Atlantic ports and Antarctica in a near future. Research on the marine communities of the Southwestern Atlantic is pressingly needed to establish pre-invasion communities and detect new introductions. Simultaneous surveillance of ports (invasion hubs) and vessels (vectors) can effectively detect invaders and inform prevention efforts in this region.