Ostracoda (Crustacea) as ecological indicators: a case study from Iberian Mediterranean brooks

Although ostracods are common inhabitants of most types of continental wate r bodies, their ecologies are generally poorly known. Despite this, there i s a genuine need for data on species-habitat relationships, particularly be cause of the recent expansion of their use in Quaternary palaeoecology. We studied the responses of ostracod assemblages to environmental gradients in a variety of Mediterranean brooks. These differed in their geographical an d geological settings, water chemistries and degrees of anthropogenic distu rbance. The use of Canonical Correspondence Analysis (CCA) showed that the main sources of assemblage variation were related to the physical and chemi cal properties of the host environment. CCA separated species that inhabite d chloride-rich, shallow streams on evaporitic rocks at medium altitudes, f rom deeper, lowland streams with higher carbonate than chloride contents. T he second axis of CCA reflected ostracod species segregations derived from nutrient (nitrate) pollution of aquifers. It also showed a gradient from hi gh altitude sites with high BMWP' values, to disturbed lowland sites that w ere nitrate-enriched and had high oxygen concentrations. Multivariate logis tic regression showed that Sarscypridopsis lanzarotensis and Heterocypris s alina both relate to waters with low alkalinities with respect to calcium a nd, in the former case, also to high relative chloride contents. Both speci es are good indicators of aquatic ionic composition, which is related to lo cal geology. Our results also suggest that Herpetocypris brevicaudata, a co mmon ostracod in the area, may be valid as indicator of clean waters. Despi te these findings, further data are required before Ostracoda can be used e ffectively to monitor water quality. However, the present survey provides e vidence that supports their potential in the assessment of the present and past conditions of flowing waters.