| Summary: | Oceans are becoming more acidic as a consequence of absorbing elevated levels of atmospheric CO2 , a process known as ocean acidification (OA). Responses to OA are likely related to an organisms' natural habitat and their capacity to buffer environmental change. Few studies assess physiological impacts on coastal intertidal organisms living in environments with C02--induced pH minima lower than IPCC OA projections for year 2100. We used an intertidal crab, Petrolisthes cinctipes, to explore variation in energetic processes across early life-history stages during exposure to low pH. Physiological mechanisms allowing larvae to transition from stable pH environments (pelagic) to habitats with pH fluctuations (intertidal zone) are poorly understood. To determine whether metabolic responses to OA vary among early developmental stages we measured metabolic rates, total protein, dry weights, total lipids and C/N in embryos, larvae and juveniles reared in ambient (7.96±0.04) or low pH (7.60±0.06). Embryos exposed to pH 7.60 displayed 11% and 6% lower metabolism and dry weight, respectively. However, responses varied by clutch indicating significant maternal effects among six females. Larval and juvenile metabolism was not affected by C02. Larvae contained 7% less nitrogen and C/N was 6% higher in individuals reared at pH 7.60, representing a switch from lipid to protein metabolism. Dry weight was 19% reduced in juveniles after 8 d in pH 7.60, however differences disappeared at 33d suggesting compensation after long-term exposure. Differences in energy partitioning likely underlie varying sensitivities to OA among stages and clutches. Understanding organism responses to high C 0 2 in variable pH environments is vital in predicting future influences of OA on near-shore ecosystems.
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