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Abstract: Heat shock proteins are important components in the cellular defense against proteotoxic stress. This work aimed to reveal HSP70 (hsc70 plus hsp70) expression patterns in several marine species (fish, crabs and shrimps) within a community along a temperature gradient and at the upper thermal limit. The organisms were collected in the Tagus estuary and adjacent shore (in Cabo Raso), Portugal. Exposure trials were performed using the critical thermal maximum (CTMax) method in order to recreate a stress gradient of ecological relevance. Protein analysis was performed using an enzyme linked immunosorbent assay (ELISA). Organisms within each community (estuary, coast; subtidal, intertidal, supratidal) responded in several different ways: no change in HSP70 levels, an increase in HSP70 levels, or increases and decreases in HSP70 levels. These patterns of response occurred independently of taxa, CTMax and habitat type. Magnitude of expression relates to the habitat''s thermal conditions. Species from highly variable and hot habitats i.e. intertidal/supratidal zone, and living in greater shore heights produce higher amounts of HSP70. Demersal and subtidal species inhabit colder and more stable waters thus they seem to have a slower heat shock response. No clear pattern was observed for species of the same group (fish, crabs and shrimps) or congeneric species. HSP70 expression showed high intraspecific variability potentially due to genetic traits, environmental traits and condition status. [Copyright &y& Elsevier]