The marine hermit crabs, Clibanarius taeniatus (H. Milne-Edwards, 1848) and C. virescens (Krauss, 1843) are common rocky intertidal species along the coast of Queensland, Australia. Laboratory experiments in dilute (8‰) seawater at 15°, 25° and 35°C over an extended period (up to 77 h) showed that C. taeniatus had significantly better survival than C. virescens. In extended exposure to a low salinity, estuarine environment C. taeniatus also survived significantly better than C. virescens. Repeated sampling at selected sites revealed that a site with no freshwater influence maintained a low percentage of C. taeniatus and high percentage of C. virescens, while at a site influenced by regular, low level freshwater runoff, the percentage of C. taeniatus remained high. A survey of the Queensland coast, showed that C. virescens tended to be more dominant on open coasts uninfluenced by freshwater, while C. taeniatus tended to be more abundant in areas influenced by freshwater. These two species therefore are a convenient indicator system for the influence of freshwater on tropical intertidal rocky shores and may therefore constitute an important management tool in areas experiencing coastal development with concomitant storm water runoff into marine habitats.