Combined effects of temperature and ocean acidification on the juvenile individuals of the mussel Mytilus chilensis

Anthropogenic CO₂ emissions have led to increasing global mean temperatures (a process called global warming) and ocean acidification. Because both processes are occurring simultaneously, to better understand their consequences on marine species their combined effects must be experimentally evaluated. The aim of this study was to evaluate for the first time the combined effects of ocean acidification and water temperature increase on the total calcification rate, growth rate and survival of juvenile individuals of the mytilid mussel Mytilus chilensis (Hupe). Two temperature levels (12 and 16°C) and three nominal CO₂ concentrations (390, 700 and 1000ppm of CO₂) were used. We found that the net rate of calcium deposition and total weight were not significantly affected by temperature, but were negatively affected by the levels of CO₂. The interactive effects of temperature and CO₂ levels affected only the shell dissolution, but this process was not important for the animal's net calcification. These results suggest that individuals of M. chilensis are able to overcome increased temperatures, but not increments of CO₂ levels. It is well known that mussels influence their physical and biological surroundings. Therefore, the negative effects of a CO₂ increase could have significant ecological consequences, mainly in those habitats where this group is dominant in terms of abundance and biomass. Finally, taking into account that this species inhabit a wide geographic range, with contrasting environmental conditions (e.g., temperature, salinity and, pH), further studies are needed to evaluate the intraspecific variability in the responses of this species to different environmental stressors.