This project concluded the first systematic research on spatial and temporal distribution of ecotoxic trace metals (Cd, Cu, Hg, Pb and Zn) in aquatic anchialine ecosystems. These systems are partly submerged speleological objects with highly stratified water column. Significantly elevated trace metal concentrations in both anchialine caves (Bjejajka and Lenga, Mljet National Park) compared to adjacent seawater, were of natural origin. Anchialine caves could be used as suitable natural laboratories for investigation under conditions that are present in deep oceans.