Does change in an adriatic hydromedusan fauna indicate an early phase of marine ecosystem destruction?

One of the most critical problems in human efforts to combat consequences o f pollution is the proper identification of the initial phases of ecosystem disturbance. Investigation of hydrographic conditions and medusan species composition in the Northern Adriatic region from 1992 to 1997 showed persis tence of hypoxic conditions and low numbers of meroplanktonic hydromedusae. The changes observed in the hydromedusan fauna demonstrate one aspect of t he long-term consequences of oxygen deficiencies in marine ecosystems: decr eased biodiversity. We suggest that the species composition of meroplankton ic hydromedusae may be a useful indicator of the early phase of such change s.