As the sea surface temperatures in the North Atlantic Ocean continue to rise , it will be imperative to understand how increased temperature will affect ectothermic organisms such as Mytilus spp . Innerpollen , Norway is a shallow, pond-like inlet with limited water exchange with the open ocean during summer months, exposing wild mussels to high water temperatures (19.9 ± 1.8°C , 13.1-26.7°C July-August) . Approximately 11 km southwest of Innerpollen lies the IMR research station on the island of Austevollmussels are exposed to comparatively cooler water temperatures (15.0 ± 0.9° C, 11.0-20.0°C July-August) . Mussels were collected from these sites with the objective of comparing the thermal biology of animals originating from distinct thermal environments. Mussels were held under four temperatures ( 15, 20, 25, and 30°C) and their thermal biology was characterized using: (1) median lethal time (LT50), (2) valve gaping behaviours , (3 ) respiration, and (4 ) feeding rates, where physiological rates were measured after a 7-day exposure to the target temperature. Differential physiological and behavioural responses between mussel sources suggest that individuals from Innerpollen outperform those from Austevoll at 25° C and above , as exhibit ed by increased survival. This study highlights the potential for mussels from distinct thermal environments within a close geographic range to have diverse responses to future climatic scenarios , which could provide insight to how the distribution or abundance of mussels may be affected by increasing temperatures due to differences in survival between sources. Results could have important ecological implications for Norwegian waters and can assist in identifying traits associated with thermal tolerance, which could have applications to selective breeding programs for mussel aquaculture within Europe.