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According to the entity, the zebra mussel (Dreissena polymorpha) is an invasive exotic species in clear expansion throughout much of the Iberian Peninsula. Its effect as a transformer of the environmental conditions where it is located, its impact on other native species, some of them threatened, and its effect on water facilities threatens the habitats where it is housed.

In 2008, a Zebra Mussel Vulnerability Index (IVMC) was developed, which made it possible, according to the University of Lleida, to establish with sufficient precision, the degree of vulnerability of the water bodies of the Ebro hydrographic demarcation to this species and the potential severity of its presence.

This project aims to be applied in the revision and updating of the structure and variables of the IVMC, taking as a reference the current distribution of the zebra mussel in pre-selected water masses for their variability and representativeness, belonging to different Spanish river basins where their presence is known. Once the new IVMC has been calibrated, it would be applied to all the bodies of water proposed by the hydrographic confederations, to obtain a detailed database of the vulnerability and severity of the effects.

The main objective of the project has been the creation and validation of an indicator system of the vulnerability of continental water bodies to the zebra mussel and application in the different river basin districts participating in the project, as a basis for population control actions based on hydraulic and hydrological management and possible climate change scenarios.

The specific objectives are:

• Review of the Zebra Mussel Vulnerability Index (IVMC). Update of its structure, variables and quantification ranges.
• Characterization of the geographical distribution of the zebra mussel in Spain. Analysis of the recognised ecological and socio-economic effects and the control measures applied.
• Calibration of the Zebra Mussel Vulnerability Index (IVMC).
• Protocol for the application of the new Zebra Mussel Vulnerability Index (IVMC).
• Calculation of the vulnerability and severity of the presence of zebra mussels in the different river basins participating in the project.
• Evaluation of the effectiveness of possible zebra mussel population control actions in various scenarios.
• Dissemination of project results.

• Bibliographic review of recent studies (under 12 years old) on biology and ecology of zebra mussels in Spain.
• Update of the variables of the Zebra Mussel Vulnerability Index (hereinafter IVMC) and its quantification ranges, based on the new information available.
• Compilation of information on the geographical distribution of zebra mussels in Spain, their documented ecological and socio-economic effects and the control measures applied.
• Selection of a varied sample of representative water bodies of different limnological characteristics (relating to aquatic ecosystems mainly lakes, reservoirs, rivers and wetlands) and socioeconomic inhabited and uninhabited by zebra mussel populations, within the framework of the hydrographic confederations participating in the project.
• Application of the updated IVMC to the selected sample. Analysis of results (precision ranges and tolerances). Implementation of possible readjustments.
• Development of an automated tool for calculating the new IVMC.
• Presentation of the new IVMC, through a technical document describing its operation (application protocol) and its dissemination through the hydrographic confederations participating in the project.
• Generation of a database with the IVMC variables, of the water bodies proposed by each hydrographic confederation participating in the project.
• Selection of water bodies in each participating river basin district with active or planned zebra mussel population control measures.
• Characterisation (description and grouping by type) of active or planned population control measures, based on hydraulic management and use management, of water bodies.
• Preparation of a synthesis document for the incorporation of the results of the study into the National Strategy for the Control of the Zebra Mussel (Dreissena polymorpha) in Spain.
• Dissemination and communication actions of the project.

According to the results of the project, zebra mussel populations inhabit at least 83 bodies of water, belonging to 7 river basin districts. The current distribution of the species assumes an expansion rate of about four to five new bodies of water each year, since 2002.

The impact of the species at an ecological and socioeconomic level and the low degree of study in Spain are also highlighted. The project carried out by the University of Lleida (UdL), has consisted of developing an early warning system against the zebra mussel, which measures the vulnerability of bodies of water not inhabited by the species, as well as the potential severity of their eventual colonization. This system is based on an update of the IVMC Index (Zebra Mussel Vulnerability Index) that the entity developed in 2008 and which made it possible to establish with sufficient precision the degree of vulnerability of the water bodies of the Ebro hydrographic demarcation to this invasive exotic species. Along with the update of the IVMC, a computer application has been developed that allows the quick, easy and secure calculation of the IVMC.

The results of the project on a sample of 46 available water bodies, without and with zebra mussels, from five peninsular river basin districts (Miño-Sil, Eastern Cantabrian/Basque Country, Ebro, Segura and Guadiana) has quantified the current degree of vulnerability of these water bodies, indicating that the river basin district most vulnerable to the species, among the five considered, it is that of the Ebro, followed by the hydrographic demarcation of the Segura. According to the entity, the Eastern Cantabrian/Basque Country basin also has a high level of vulnerability, although there are still few bodies of water affected.

By comparison between the IVMC in colonized and non-colonized water bodies, it can be inferred that the control measures applied to date have had very limited effectiveness. However, the objective of the IVMC is to estimate the vulnerability of water bodies where the zebra mussel is not yet present, in order to direct attention and control towards the most vulnerable. The IVMC also allows simulating scenarios, particularly of local changes (e.g., changes in control measures on recreational activities and uses of water bodies), as well as global changes (variations in the hydrological regime and/or water temperature). The project carried out complies with one of the measures proposed in the National Strategy for the Control of Zebra Mussels in Spain and has generated a document that can contribute to the updating of this strategy published in 2007.