title: Temperature tolerance of different larval stages of the spider crab Hyas araneus exposed to elevated seawater PCO2.
abstract: BACKGROUND
  Exposure to elevated seawater PCO2 limits the thermal tolerance of crustaceans but the underlying mechanisms have not been comprehensively explored. Larval stages of crustaceans are even more sensitive to environmental hypercapnia and possess narrower thermal windows than adults.
  
  
  RESULTS
  In a mechanistic approach, we analysed the impact of high seawater CO2 on parameters at different levels of biological organization, from the molecular to the whole animal level. At the whole animal level we measured oxygen consumption, heart rate and activity during acute warming in zoea and megalopa larvae of the spider crab Hyas araneus exposed to different levels of seawater PCO2. Furthermore, the expression of genes responsible for acid-base regulation and mitochondrial energy metabolism, and cellular responses to thermal stress (e.g. the heat shock response) was analysed before and after larvae were heat shocked by rapidly raising the seawater temperature from 10°C rearing temperature to 20°C. Zoea larvae showed a high heat tolerance, which decreased at elevated seawater PCO2, while the already low heat tolerance of megalopa larvae was not limited further by hypercapnic exposure. There was a combined effect of elevated seawater CO2 and heat shock in zoea larvae causing elevated transcript levels of heat shock proteins. In all three larval stages, hypercapnic exposure elicited an up-regulation of genes involved in oxidative phosphorylation, which was, however, not accompanied by increased energetic demands.
  
  
  CONCLUSIONS
  The combined effect of seawater CO2 and heat shock on the gene expression of heat shock proteins reflects the downward shift in thermal limits seen on the whole animal level and indicates an associated capacity to elicit passive thermal tolerance. The up-regulation of genes involved in oxidative phosphorylation might compensate for enzyme activities being lowered through bicarbonate inhibition and maintain larval standard metabolic rates at high seawater CO2 levels. The present study underlines the necessity to align transcriptomic data with physiological responses when addressing mechanisms affected by an interaction of elevated seawater PCO2 and temperature extremes.
authors.affiliation: Integrative Ecophysiology, Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Schiffer
authors.affiliation: Scientific Computing, Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: Lars
authors.initials: L
authors.lastname: Harms
authors.affiliation: Integrative Ecophysiology, Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: Magnus
authors.initials: M
authors.lastname: Lucassen
authors.affiliation: Integrative Ecophysiology, Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: Felix Christopher
authors.initials: FC
authors.lastname: Mark
authors.affiliation: Integrative Ecophysiology, Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: Hans-Otto
authors.initials: HO
authors.lastname: Pörtner
authors.affiliation: Integrative Ecophysiology, Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Storch
keywords: Climate change; Gene expression; Hyas araneus; Larvae; Ocean acidification; Thermal tolerance