The Hydradephaga of the Segura basin (SE Spain): twentyfive years studying water beetles (Coleoptera)

We present the results of 25 years of study of the faunistics, biogeography, ecology and conservation of the Hydradephaga of the Segura river basin. Eighty one species have been recorded from the area, ca. 45% of the total of species found in the Iberian peninsula. Six of them are Iberian endemics, and fourteen are considered to be rare within the basin, although most of these are not rare in an Iberian context. The phenetic hierarchy of relationships among the western-Palaearctic regions considered shows a clear similarity of the fauna of the Segura basin with that of the Maghreb, which, together with the rest of the Iberian fauna form a well defined group isolated from the rest of the European areas. Within the Iberobalear region, there is also a clear north-south division, with a secondary classification into western and eastern basins. The Balearic islands seem to be a relatively independent biogeographical unit, although more related with the southern cluster. The environmental characteristics determining the distribution of the Hydradephagan fauna in the study area, as determined by Correspondence Analysis, are altitude, degree of mineralization of the water, and amount and type of riparian vegetation. Using a semi-quantitative scoring system to evaluate the vulnerability of the species only Hydroporus decipiens had a vulnerability value considered to be high (9), due to its rarity within the basin and to its general restricted distribution, although the incomplete knowledge of its distribution and taxonomy could be a distorting factor. With a similar value (8), Nebrioporus baeticus is a typical inhabitant of saline running waters, highly endangered habitat due to the increasing use of irrigation in the surrounding fields. The stations with the highest conservation interest were mountain streams in the NW of the basin, which are also of high conservation interest for other aquatic Coleoptera (e.g. Hydraenidae). A disadvantage of the index applied (IC, “conservation interest”) is the lack of reference to the conservation interest of habitats outside the study area. Thus, the saline or hypersaline streams, which are extremely rare in an European (or even global) context, are not considered of particular relevance due to the poor species richness and local abundance. The use of other criteria for the selection of sites of conservation value, such as complementarity, could overcome this limitation.