Long-term exposure of Mytilus galloprovincialis to temperatures beyond 26oC triggers mussels' mortality. The present study aimed to integratively illustrate the correlation between intermediary metabolism, Hsp gene expression and oxidative stress related proteins in long-term thermally stressed Mytilus galloprovincialis and whether they are affected by thermal stress' magnitude and duration. We accordingly evaluated the gene expression profiles, in the posterior adductor muscle (PAM) and the mantle, concerning hsp70 and hsp90, and the antioxidant defense indicators Mn-SOD, Cu/Zn-SOD, catalase, glutathione S-transferase, and the metallothioneins mt-10 and mt-20. Moreover, we determined antioxidant enzymes' activities, oxidative stress through lipid peroxidation and activities of intermediary metabolism enzymes. The pattern of changes in relative mRNA expression levels indicate that mussels are able to sense thermal stress even when exposed to 22oC and before mussels' mortality is initiated. Data indicates a close correlation between the magnitude and duration of thermal stress with lipid peroxidation levels, changes in the activity of antioxidant enzymes and the enzymes of intermediary metabolism. The gene expression and increase in the activities of antioxidant enzymes support a scenario, according to which exposure to 24oC might trigger ROS production, which is closely correlated with anaerobic metabolism under hypometabolic conditions. Increase and maintenance of oxidative stress in conjunction with energy balance disturbance seems to trigger mussels' mortality after long term exposure at temperatures beyond 26oC. Eventually, in the context of preparation for oxidative stress, certain hypotheses and models are suggested, integrating the several steps of cellular stress response.

The role of thermal stress phenomena in setting stratified distribution limits was investigated in the bearded horse mussel Modiolus barbatus in response to the seasonal temperature regime in the field. Mussels were transplanted from their natural depth range at ca. 20 m to 3 m depth, where they then experienced enhanced variability of ambient conditions. In specimens from both depths, thermal stress was assessed from the inducible heat shock response (HSR), the accumulation of irreversibly damaged proteins, and from metabolic characters including the putative shift from aerobic to anaerobic metabolism. During both winter and summer, the HSR became involved more at shallow depths than at 20 m depth. The accumulation of succinate during summer indicates transition to anaerobiosis. The results suggest that the development of anaerobic conditions and the exploitation of the HSR are closely intertwined. The field data corroborate that glycolytic capacity, the level of energy turnover, and also protection from protein damage play a role in setting passive tolerance to extremes in environmental temperature. We suggest that limits to vertical distribution of M. barbatus are set by the time and degree of exploitation of the mechanisms sustaining passive thermal tolerance and the avoidance of protein damage in the warmth. KEY WORDS: Bivalves · Modiolus barbatus · Environmental warming · Physiological patterns · Heat shock response · HSR Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 449: [183][184][185][186][187][188][189][190][191][192][193][194][195][196] 2012 warming at ecosystem level will build on speciesspecific responses (Pörtner 2001, Somero 2010. For reliable projections of future changes it is important to develop a mechanism-based cause-and-effect understanding. The latter must be integrative and encompass effects of climate change at various levels of biological organization, from molecular, cellular, organismal, population, and community-ecosystem.Many laboratory studies have defined the thermal limits and thermotolerance of bivalves by studying the expression of heat shock proteins (Hsps) (Hofmann & Somero 1995, Buckley et al. 2001. Hsps may co-define extreme thermal limits, and it has been hypothesized that they are related to species boundaries in intertidal ecosystems (Hofmann 2005, To manek 2010. Moreover, physiological processes such as heart functioning or metabolic adaptations setting aerobic scope through regulated capacities of glycolytic and mitochondrial metabolism, including the respiratory chain and the tricarboxylic acid cycle, appear equally important and may even take priority in determining the thermal windows of species, and thereby biogeographical limits. Their limited capacity at thermal limits may also be crucial in initiating the heat shock response (HSR) (Pörtner 2001, Braby & Somero 2006, Anestis et al. 2007, Somero 2010. Following the principles of the concept of oxygen and capacity limited thermal tolerance (OCLTT), the ...