Ecology and distribution of ostracods associated with flowing waters in the eastern Iberian Peninsula

The ostracod fauna of the three main rivers of the central Mediterranean sl ope of the Iberian Peninsula was studied, with special attention being paid to ecology and distribution. Forty-six stations were sampled in spring and autumn 1995 and thirty ostracod species were collected, two of these (Traj ancypris serrata and Heterocypris reptans) new to the Iberian fauna. The mo st common species were Ilyocypris bradyi, Herpetocypris brevcaudata, Cyprid opsis vidua. and Limnocythere inopinata. Cluster analysis showed that these species, together with Ilyocypris inermis and Sarscypridopsis spp. form th e most widespread ostracod assemblage in the area, although its widespread distribution is not related to any of the environmental variables monitored . However, factors such as attitude, mean January air temperature, distance from source, Row discharge, water quality, and degree of organic pollution play an important role in explaining the occurrence of less common species . One species group was linked to high elevations and BMWP' biotic index va lues and low winter temperatures. Candona neglecta best characterizes this assemblage. In the apposite part of this environmental gradient, Ilyocypris gibba, associated with lower altitudes. epitomizes the third species group . Heterocypris salina and Heterocypris incongruens were the species that we re most tolerant of organic pollution. Our results are compared with those reported in studies from different habitats (e.g., springs) and latitudes. The implications of our findings for paleoenvironmental reconstruction and water resources management are discussed.