Abstract
Ocean acidification (OA) is altering the chemistry of the world’s oceans at rates unparalleled in the past roughly 1 million years. Understanding the impacts of this rapid change in baseline carbonate chemistry on marine organisms needs a precise, mechanistic understanding of physiological responses to carbonate chemistry. Recent experimental work has shown shell development and growth in some bivalve larvae, have direct sensitivities to calcium carbonate saturation state that is not modulated through organismal acid-base chemistry. To understand different modes of action of OA on bivalve larvae, we experimentally tested how pH, PCO2, and saturation state independently affect shell growth and development, respiration rate, and initiation of feeding in Mytilus californianus embryos and larvae. We found, as documented in other bivalve larvae, that shell development and growth were affected by aragonite saturation state, and not by pH or PCO2. Respiration rate was elevated under very low pH (~7.4) with no change between pH of ~ 8.3 to ~7.8. Initiation of feeding appeared to be most sensitive to PCO2, and possibly minor response to pH under elevated PCO2. Although different components of physiology responded to different carbonate system variables, the inability to normally develop a shell due to lower saturation state precludes pH or PCO2 effects later in the life history. However, saturation state effects during early shell development will carry-over to later stages, where pH or PCO2 effects can compound OA effects on bivalve larvae. Our findings suggest OA may be a multi-stressor unto itself. Shell development and growth of the native mussel, M. californianus, was indistinguishable from the Mediterranean mussel, Mytilus galloprovincialis, collected from the southern U.S. Pacific coast, an area not subjected to seasonal upwelling. The concordance in responses suggests a fundamental OA bottleneck during development of the first shell material affected only by saturation state.
Highlights
The uptake of carbon dioxide by ocean waters due to increasing atmospheric CO2 concentrations and resulting change in marine carbonate chemistry is called ocean acidification
We highlight these challenges for others who may want to take this experimental approach, as PCO2 is highly sensitive to small changes in the ratio of alkalinity to Dissolved inorganic carbon (DIC) (Table 1), even though our expected and measured DIC and total alkalinity values were in very close concordance (Fig 2)
We utilized a unique experimental approach to determine the response of shell development, shell growth, respiration rate, and doi:10.1371/journal.pone.0128376.g007
Summary
The uptake of carbon dioxide by ocean waters due to increasing atmospheric CO2 concentrations and resulting change in marine carbonate chemistry is called ocean acidification. During absorption and hydrolysis of CO2 by marine and estuarine waters a number of changes occur to the carbonate chemistry system: dissolved inorganic carbon increases, PCO2 increases, pH decreases, and the calcium carbonate saturation state decreases These changes are well understood and can be predicted using well-documented thermodynamic constants. Many temperate coastal zones are highly productive (or even eutrophic), with seasonal and daily peaks in production-respiration cycles related to the timing of freshwater delivery, light, stratification, and temperature [11,12,13] Subjected to this variability, reproduction in many marine invertebrates is timed to take advantage of the optimal conditions to help ensure success of the sensitive larval stages [14], [15]. Such an interpretation is not entirely possible with many of the currently used experimental methods
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
