Azolla filiculoides invasion in the Doñana marshland (Spain)
The Doñana marshland in Southwest Spain is one of the most extensive protected marshland networks in Europe covering over 360 km2. Azolla filiculoides (Azollaceae: EPPO Observation List of Invasive Alien Plants) an invasive aquatic fern species native to North America was first recorded in the marsh in 2001. Since this first record the occurrence of A. filiculoides has been mapped throughout the marsh using medium resolution remote sensing Landsat satellites. Since 2001, the annual variation in the cover of A. filiculoides has varied considerably ranging from approximately 400 ha in 2001 to 1600 ha in 2007 where cover was at its highest. Over ten years when the mapping of A. filiculoides took place, the average minimum temperature during the summer and winter months was shown to increase. In this study it was shown that there was a positive relationship between the annual cover of A. filiculoides and air temperature in the winter months. Warmer winter temperatures may promote the growth of A. filiculoides early in the season before the spring establishment of submerged macrophytes. At present Azolla management has not been attempted within the Doñana marshland – the Azolla biological control agent Stenopelmus rufinasus (Coleoptera: Curculionidae) has not been recorded at the site but it is present in the wider vicinity. The potential negative effect of A. filiculoides on native macrophyte abundance necessitates careful monitoring of the population and integrated control programmes throughout the marshland network.
Espinar JL, Días-Delgado R, Bravo-Utrera MA, Vilà (2015) Linking Azolla filiculoides invasion to increased winter temperatures in the Doñana marshland (SW Spain). Aquatic Invasions 10, 17–24.