The rapid variation of global climate occurring in the last decades together with the consequential effect on the whole life forms has originate an accurate multidisciplinary exploration on the cause, the status and the potential relapse of these environmental alteration. A central goal in exploring the consequences of global climate change is to accurately predict the alteration of thermal stresses on organisms together with the subsequent modification of animal distribution and populations/species diversity. The aim of the present project is to investigate the physiological tolerance and the adaptative flexibility of two marine model organisms in order to forecast and test the animal resilience to the effect of global climate change. The hypothesis consider that the species tolerance range could be narrower in particular selective stages and distribution, the “weakest links”, as at the edges of geographical distribution or in gametes and early ontogenetic stages. The physiological analyses will be addressed to successive hierarchical levels from molecular to cellular to organismic, in order to achieve the broader possible scenario. The researches will be focused on different aspects of respiratory, circulatory and metabolic physiology, on the temperature kinetics and the thermodynamics of selected enzymes, on the modification of protein expressions, and on the metabolic performances of sperm and eggs. This information then will be used, alone and in combination with data from the literature, to test models of global climate change and its relevant effect on marine populations in different thermal and geographical regions. All the results will finally converge into a theoretical evaluation providing further indications on the climate change influences on ecosystems.