Both the physiology and distribution of intertidal organisms are strongly influenced by different kinds of physical stress. Temperature, UV radiation and desiccation in low tide conditions are usually considered the most important physical stresses. These factors impact cell metabolism, and the organism´s ability to rapidly adapt to altering environmental conditions sets its tidal distribution limits. The role of the HSP70 protein (stress protein) family in thermal stress responses has been widely demonstrated. Although it has been shown that stress protein expression is a useful tool to quantify part of this physical stress, few studies have been made with different in situ intertidal organisms. To test differences in HSP70 expression under natural conditions in the intertidal environment, we chose a common cnidarian of the eastern Pacific Ocean: the anemone Anthopleura elegantissima. Polyp HSP70 expression depends on the degree of emersion and the extent of physical stress (0.1-3.6 ± 1.5 ng HSP70 mg Protein-1 were registered between fully immersed and fully emersed polyps of the same clone). The time of immersion is reflected in the recovery of polyp HSP70 levels from the high tidal exposure (reaching again as shallower clones express more HSP70 (2.5 ng HSP70 mg P-1), than deeper ones (0.1 ng HSP70 mg P-1). Also sunny and foggy environmental situations influence the stress response. Anemone clones exposed to the sunny high intertidal zone express more than three times HSP70 (2.2 ng HSP70 mg P-1) than those on a foggy high intertidal day (0.6 ng HSP70 mg P-1). For A. elegantissima, shrinking of polyps, mucus secretion, sand covering, UV absorbing molecules, and a tight patch structure work concurrently with HSP70 expression to alleviate the effects of physical stress in low tidal emersion.