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Assessment of Zebra Mussel (Dreissena polymorpha) Infestation Risk Using GIS for Water Basins in the North-West Bulgaria

Contract No. N62558-05-P-0476
Project No. R&D 1021-EN-01
Co-ordinator: Institute of Zoology, Bulgarian Academy of Sciences
Project Manager: Prof. Dr Mladen Zivkov, DSc

Project Duration: 2005 - 2006

Funding: U.S. Army Engineer Research and Development Center's International Research Office

Project Summary:
In Bulgaria, zebra mussel (Dreissena polymorpha) occurred originally in the Danube River and the Black Sea coastal lakes and rivers. During the last 10 years a rapid spread of this species in the inland water bodies has been observed. Two of the reservoirs in the North-West Bulgaria have been reported as infested. The goal of the present study was to determine the risk of zebra mussel infestation in this region by combining available biological and environmental data and by subsequent processing and analyzing of these data using Geographic Information System (GIS). This is the first step in developing an action plan for vulnerable regions in Bulgaria.

The evaluation of physical and chemical characteristics of water bodies and their suitability to the zebra mussel requirements was made based on existing data from monitored river stations, spatial data and reservoir field survey. Fifteen reservoirs were sampled to determine which physicochemical variables explain the occurrence and abundance of zebra mussel. The principal component analysis used showed that the first two principal components related mainly to calcium concentration, pH, electroconductivity and Secchi disk transparency, explained the majority of total variance of data. pH, calcium concentration and dissolved oxygen were selected as habitat suitability parameters, and corresponding tolerance ranges based on the environmental requirements of zebra mussels during the larval and early growth stages, were defined. These parameters were divided into three main categories that reflected the infestation potential of zebra mussel: Low, Moderate and High. After all spatial and attributive data were collected, they were processed and analyzed in a GIS environment, which included the GIS database development, spatial and geostatistical interpolation of limiting factors, reclassification and overlay.

The results showed that based on water chemistry, 63.81% of the territory can be classified with high potential, 15.45% - with moderate potential, and 20.74% - with low potential for zebra mussel infestation. Additional factors in reservoirs contributing to the increased risk of infestation are large surface area (over 90 ha) and depth, high substrate diversity, moderate amount of nutrients and easy accessibility to human users. As potential zebra mussel dispersal mechanisms were identified the direct waterway connections with the Danube, as well as transport of larvae or adult individuals with fishing equipment, boats and fish stocking material from the Danube and fish farms nearby.

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Photo: R. Kennedy

Photo: R. Dimitrov

Photo: D. Kozuharov


This website is developed with support from the Bulgarian Science Fund, Ministry of Education, Youth and Science,
within the Project "Assessment and Management of Dreissena spp. Invasions in the Bulgarian Water Bodies",
Contract Number: DO-02-283/2008.

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