Zebra mussel invasion in Spain is irreversible, experts say

Scientists from the Faculty of Biological Sciences -- University of Valencia have led a statewide project funded by the Ministry of Environment with 690,000 Euros to characterize eleven Spanish populations of zebra mussels (Dreissena polymorpha). Project leader Professor Amparo Torreblanca of the Department of Functional Biology and Physical Anthropology explains that the mussel "is capable of adapting to different environmental conditions, including chemical pollution, and shows a prolonged reproductive period."

The comprehensive ecophysiological and genetic characterization of zebra mussel populations developed by researchers at the University of Valencia together with the Spanish National Research Council (CSIC) (through the Institute of Environmental Diagnosis and Water Research (IADEA) of Barcelona and the Institute of Aquaculture Torre de la Sal (IATS) of Castelló) will enable governments to devise specific strategies of control, as well as to create new methods to combat its future spreading in natural water areas or enclosed facilities. Moreover, the high rate of reproduction detected in the hormonal study suggests that the practice of water sports such as canoeing "should imply a strict adherence to the recommendations of the public bodies that manage the water resources in order to prevent its spread to other rivers of the peninsula or the continent, because mussel larvae easily hook to boats," says Torreblanca.

The zebra mussel is an invasive species that has proliferated in rivers and lakes in Spain and North America in recent decades. It arrived from the basins of the Black and Caspian seas, and is a serious environmental and socioeconomic problem. In Spain, the first populations were detected in 2001 in the Flix reservoir, from where there was a gradual spread to other reservoirs in the Ebro basin and other points of ecological interest until fully colonizing the basin. In addition, river Júcar was affected. The first population was found here in 2005 in the Sitjar reservoir on the river Mijares, and is now stabilized according to the researchers, while in the swamp Forata in Magro, a tributary of Júcar, the zebra mussel was found in 2006 but in the last two years there has been no sign of larvae. However, one can not completely rule out their presence. This invasion, according to the work coordinated by Amparo Torreblanca, "has not been produced directly from the original basins, but has come from Western populations, ie from areas geographically much closer."

The expansion of the zebra mussel has not only an environmental impact because of its impact on endemic species and on the environmental balance of ecosystems, but also a great economic impact. Amparo Torreblanca recalls that invasion of this species since the eighties has cost the United States millions of dollars, while the Confederación Hidrográfica del Ebro predicted in 2005 that the zebra mussel expansion would cost about 40 million Euros over twenty years. This is because the mollusk "creates significant problems and economic costs due to its ability to block all types of infrastructure and water pipes," adds the professor.

The control of the zebra mussel requires a huge knowledge of the main sources of colonization, dispersal ability, as well as the mechanisms and environmental factors that can regulate their growth and reproduction. For this reason, the project coordinated by scientists at the University of Valencia has studied ten populations of the Ebro basin and one of the Jucar, sampled at points with different water quality in order to get their characterization from various parameters such as genetic, ecophysiological, genomics and proteomics.

For example, they have determined the levels of metallothionein in the digestive gland and gills, a protein that indicates exposure to metals. In addition, among other actions, they have evaluated the responses of these populations of zebra mussels to heat stress and lack of water by determination of protein HSP70, while proteomic techniques have been used to detect changes in the global patterns of the protein expression of this invasive species. Thus, for the first time, "we have found unique metabolic pathways in the zebra mussel that can be used to develop specific treatments for their control," says Torreblanca.