Rapid expansion and potential range of the invasive kelp Undaria pinnatifida in the Southwest Atlantic

Coastal Patagonia, often regarded as a pristine area of the world, has been invaded by non-indigenous species that are rapidly modifying local ecosystems. One of the most conspicuous invaders is the kelp Undaria pinnatifida. First recorded near the city of Puerto Madryn (Argentina, 42.75 degrees S) in 1992, Undaria's range has expanded more than five degrees of latitude to the south during the last 15 years. By 2007 it was first detected north of Valdes Peninsula (a natural barrier to dispersal), beginning its northward expansion, and between 2007 and 2011 spread along the coasts of San Jose and San Matias gulfs at an average rate of similar to 50 km yr(-1). A small population was detected in Mar del Plata (Argentina, 38.04 degrees S) in 2011, more than three degrees of latitude to the north, suggesting a new human-mediated inoculation. A thermal tolerance window is hypothesized based on experimental information and remotely sensed sea-surface temperature (SST) at the latitudinal range limits of U. pinnatifida populations worldwide. The window is defined by average SSTs ranging between -0.6 degrees C and 16.8 degrees C in the coldest month, and between 13 degrees C and 28 degrees C in the warmest month. Using climatologic satellite SST from several locations, a potential latitudinal thermal range extending between Puerto Deseado (Argentina, 47.75 degrees S) and Cape Torres (Brazil; 29.35 degrees S) is predicted. Salinity and substrate quality however constrain suitable habitat in the Southwest Atlantic to discrete stretches of coastline, suggesting that the northern potential boundary would be around La Coronilla (33.90 degrees S), on the Uruguayan coast.