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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.

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Abstract.Sedimentation and increasing temperature caused by human disturbances and global climate change are additive in their effects on coastal areas. To assess their influence on intertidal organisms, we studied the hermit crab, Pagurus samuelis, under acute temperature changes and shallow burial conditions. We applied three temperatures (5°C, 20°C, and 30°C) and two burial depths (3 cm and 6 cm) with a control at the surface (0 cm), and monitored survival, shell abandonment, and burial escape. Survival was primarily affected by temperature, with hermit crabs twice as likely to survive at 20°C than at 30°C, and at 5°C than at 30°C. The combined conditions of 30°C and 6 cm were the least favorable for survival. Hermit crabs which abandoned their shells were more likely to survive burial at 20°C and 30°C than those retaining their shells. Fewer hermit crabs abandoned their shells when exposed to 5°C than to 20°C and 30°C. Crabs buried at 6 cm were 85.0% less likely to abandon shells than those buried at 3 cm, and heavier shells were less readily abandoned than lighter shells. Although overall, 35% of hermit crabs escaped burial to the sediment surface, hermit crabs buried in the combined conditions of 30°C and 6 cm were significantly slower to reach the surface. Our results show that the combined stresses of temperature and burial can impact survival of hermit crabs in intertidal zones. While human activities, including dredging, industrial and domestic dumping, and coastal construction, result in relatively immediate increased inputs of sediment in coastal environments, climate change may endanger intertidal organisms, such as P. samuelis, living near their thermal tolerance over the long term, with both increasing temperature and sedimentation from more frequent storm events.