Volume 43 - Number 2 - 2008
Artículo

The invasive seaweed Undaria pinnatifida (Harvey) Suringar in Ría Deseado (Southern Patagonia, Argentina): sporophyte cycle and environmental factors determining its distribution

Juan P. Martin¹ y Ricardo Bastida^2,3

¹Unidad Académica San Julián, Universidad Nacional de la Patagonia Austral, Colón y Sargento Cabral (9310) Puerto San Julián, Argentina
¹Depto. de Ciencias Marinas, Universidad Nacional de Mar del Plata, Mar del Plata, Argentina
¹Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)

E-mail:  martin_jpablo@yahoo.com.ar

Undaria pinnatifida was registered in Ría Deseado (47º45´S, 65º55´W – southern Patagonia) by the first time in spring 2005, colonizing the intertidal and shallow subtidal. A seasonal survey in 2006 showed that U. pinnatifida was established in a sheltered zone inside the estuary, along a coastal fringe of 8 km between Punta Cascajo and Cañadón del Puerto. This continuous distribution was only interrupted in the mouth of canyons that flow into Ría Deseado, where the bottom is conformed by mud and sand. The sporophytes were mainly found colonizing the rocky bottom in the lower intertidal, bordering the Macrocystis pyrifera population. The highest density and biomass of sporophytes (12.13 ind. m^-2; 254.60 g m^-2) were registered during spring, when the population was mainly conformed by individuals of medium sizes. The lowest density and biomass (0.33 ind. m^-2; 5.69 g m^-2) were registered in autumn. Juvenile sporophytes recruited throughout the year, but presented the highest percentage in the population during autumn and winter. First mature sporophytes appeared in spring and attained their maximum size in summer. After this, the sprophytes decayed and disappeared. Environmental factors such as rocky bottoms availability and water transparency may be the main factors determining the sporophytes distribution in Ría Deseado. The field experiment point out that M. pyrifera population is an important factor controlling the dispersion of U. pinnatifida towards the subtidal

Key words: Invasive species, exotic species, life cycle, Laminariales, Macrocystis pyrifera