Heat Shock Proteins are an important component of the cellular defense against proteotoxic stress. This work aimed to uncover HSP70 expression patterns in several marine species along a temperature gradient and at the upper thermal limit. Congeneric species were compared to test genetic versus environmental influences on HSP production. Exposure trials were performed through the Critical Thermal Maximum (CTMax) method and protein analysis was performed using ELISA. Several trends in HSP70 expression profiles were identified in several species independently of taxa, CTMax and habitat type. In general, magnitude of expression relates to the habitat’s thermal conditions. In Diplodus genus HSP70 production pattern seems to be influenced by thermal conditions while in Palaemon genus it seems to be more genetically fixed. Species living on higher shore heights produce higher amounts of HSP70. Cold and stable environment species that lack an inducible Heat Shock Response or have a narrow range for HSP70 production may be vulnerable to sea warming.