Abstract
The present study suggests that the Santa Eufemia-Ereñozar karst unit in northern Iberian Peninsula is a biodiversity hotspot for groundwater oligochaetes, due to (1) the presence of a high number of stygobiotic species (corresponding to 18% of the total stygobionts known in southern Europe); (2) the comparatively high number of oligochaete species collected (corresponding to 35% of the total epigean and hypogean oligochaete species in the region); and (3) the presence of 5 species endemic to the region. A list of the oligochaete taxa found in the karst unit is presented and a conservation ranking of the cavities in the karst is proposed based on the application of four biodiversity indices (Species richness, Rarity, Vulnerability and Complementarity) to the oligochaete taxa. Vulnerability was evaluated for the first time for groundwater oligochaete taxa and it provided a useful tool to assess the protection status of oligochaetes in karstic systems. Groundwater conservation management strategies could incorporate biodiversity data from the present study.



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Acknowledgements
We are indebted to Gotzon Aranzabal, who was very helpful in speleological prospections. This work was supported by Catedra UNESCO (project UNESCO 04/04), by the Department of Environment and Regional Planning of the Basque Country and by a predoctoral grant from the University of the Basque Country for the junior author. We also wish to thank Ana I. Camacho and Steve Fend for critically reviewing the manuscript, and Boris Sket and an anonymous reviewer who helped to improve this article.
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Achurra, A., Rodriguez, P. Biodiversity of groundwater oligochaetes from a karst unit in northern Iberian Peninsula: ranking subterranean sites for conservation management. Hydrobiologia 605, 159–171 (2008). https://doi.org/10.1007/s10750-008-9331-2
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DOI: https://doi.org/10.1007/s10750-008-9331-2