Establishing the thermal threshold of the tropical mussel Perna viridis in the face of global warming

•Upper and lower thermal limits of Perna viridis established.•Hierarchy of thermal tolerance of P. viridis explored.•Failure of higher level functions occurs earlier than lower ones.•No significant hierarchical cold thermal tolerance observed.•Narrow gap of optimal thermal window for mussel despite wide survival range. With increasing recognition that maximum oxygen demand is the unifying limit in tolerance, the first line of thermal sensitivity is, as a corollary, due to capacity limitations at a high level of organisational complexity before individual, molecular or membrane functions become disturbed. In this study the tropical mussel Perna viridis were subjected to temperature change of 0.4°C per hour from ambient to 8–36°C. By comparing thermal mortality against biochemical indices (hsp70, gluthathione), physiological indices (glycogen, FRAP, NRRT) and behavioural indices (clearance rate), a hierarchy of thermal tolerance was therein elucidated, ranging from systemic to cellular to molecular levels. Generally, while biochemical indices indicated a stress signal much earlier than the more integrated behavioural indices, failure of the latter (indicating a tolerance limit and transition to pejus state) occurred much earlier than the other indices tending towards thermal extremities at both ends of the thermal spectrum.