Combined effects of short-term ocean acidification and heat shock in a benthic copepod Tigriopus japonicus Mori

Warming of the world's oceans is predicted to have many negative effects on organisms as they have optimal thermal windows. In coastal waters, however, both temperatures and pCO(2) (pH) exhibit diel variations, and biological performances are likely to be modulated by physical and chemical environmental changes. To understand how coastal zooplankton respond to the combined impacts of heat shock and increased pCO(2), the benthic copepod Tigriopus japonicus were treated at temperatures of 24, 28, 32 and 36 degrees C to simulate natural coastal temperatures experienced in warming events, when acclimated in the short term to either ambient (LC, 390 mu atm) or future CO2 (HC, 1000 mu atm). HC and heat shock did not induce any mortality of T. japonicus, though respiration increased up to 32 degrees C before being depressed at 36 degrees C. Feeding rate peaked at 28 degrees C but did not differ between CO2 treatments. Expression of heat shock proteins (hsps mRNA) was positively related to temperature, with no significant differences between the CO2 concentrations. Nauplii production was not affected across all treatments. Our results demonstrate that T. japonicus responds more sensitively to heat shocks rather than to seawater acidification; however, ocean acidification may synergistically act with ocean warming to mediate the energy allocation of copepods.