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Experimental ocean acidification leads to a shift in resource allocation and to an increased [HC[O.sub.3.sup.-]] within the perivisceral coelomic fluid (PCF) in the Baltic green sea urchin Strongylocentrotus droebachiensis. We investigated putative mechanisms of this pH compensation reaction by evaluating epithelial barrier function and the magnitude of skeleton (stereom) dissolution. In addition, we measured ossicle growth and skeletal stability. Using chamber measurements revealed that the intestine formed a barrier for HC[O.sub.3.sup.-] and was selective for cation diffusion. In contrast, the peritoneal epithelium was leaky and only formed a barrier for macromolecules. The ossicles of 6 week high C[O.sub.2]-acclimatised sea urchins revealed minor carbonate dissolution, reduced growth but unchanged stability. On the other hand, spines dissolved more severely and were more fragile following acclimatisation to high C[O.sub.2]. Our results indicate that epithelia lining the PCF space contribute to its acid-base regulation. The intestine prevents HC[O.sub.3.sup.-] diffusion and thus buffer leakage. In contrast, the leaky peritoneal epithelium allows buffer generation via carbonate dissolution from the surrounding skeletal ossicles. Long-term extracellular acid-base balance must be mediated by active processes, as sea urchins can maintain relatively high extracellular [HC[O.sub.3.sup.-]]. The intestinal epithelia are good candidate tissues for this active net import of HC[O.sub.3.sup.-] into the PCF. Spines appear to be more vulnerable to ocean acidification which might significantly impact resistance to predation pressure and thus influence fitness of this keystone species., Introduction Ocean acidification, caused by either anthropogenic C[O.sub.2] emission or seasonal changes in seawater stratification and heterotrophy, alters carbonate chemistry and thereby challenges marine organisms in terms of acid-base homoeostasis, [...]

Ocean acidification is elicited by anthropogenic carbon dioxide emissions and resulting oceanic uptake of excess C[O.sub.2] and might constitute an abiotic stressor powerful enough to alter marine ecosystem structures. For surface waters in gas-exchange equilibrium with the atmosphere, models suggest increases in C[O.sub.2] partial pressure (pC[O.sub.2]) from current values of ca. 390 µatm to ca. 700-1,000 µatm by the end of the century. However, in typically unequilibrated coastal hypoxic regions, much higher pC[O.sub.2] values can be expected, as heterotrophic degradation of organic material is necessarily related to the production of C[O.sub.2] (i.e., dissolved inorganic carbon). Here, we provide data and estimates that, even under current conditions, maximum pC[O.sub.2] values of 1,700-3,200 µatm can easily be reached when all oxygen is consumed at salinities between 35 and 20, respectively. Due to the nonlinear nature of the carbonate system, the approximate doubling of seawater pC[O.sub.2] in surface waters due to ocean acidification will most strongly affect coastal hypoxic zones as pC[O.sub.2] during hypoxia will increase proportionally: we calculate maximum pC[O.sub.2] values of ca. 4,500 µatm at a salinity of 20 (T = 10°C) and ca. 3,400 µatm at a salinity of 35 (T = 10°C) when all oxygen is consumed. Upwelling processes can bring these C[O.sub.2]-enriched waters in contact with shallow water ecosystems and may then affect species performance there as well. We conclude that (1) combined stressor experiments (pC[O.sub.2] and p[O.sub.2]) are largely missing at the moment and that (2) coastal ocean acidification experimental designs need to be closely adjusted to carbonate system variability within the specific habitat. In general, the worldwide spread of coastal hypoxic zones also simultaneously is a spread of C[O.sub.2]-enriched zones. The magnitude of expected changes in pC[O.sub.2] in these regions indicates that coastal systems may be more endangered by future global climate change than previously thought., Introduction Currently, large research efforts are directed toward studying anthropogenic climate change effects on marine ecosystems. Global warming, primarily caused by increasing C[O.sub.2] emissions, has the potential to restructure marine [...]

Marine organisms have to cope with increasing C[O.sub.2] partial pressures and decreasing pH in the oceans. We elucidated the impacts of an 8-week acclimation period to four seawater pC[O.sub.2] treatments (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 µatm) on mantle gene expression patterns in the blue mussel Mytilus edulis from the Baltic Sea. Based on the M. edulis mantle tissue transcriptome, the expression of several genes involved in metabolism, calcification and stress responses was assessed in the outer (marginal and pallial zone) and the inner mantle tissues (central zone) using quantitative real-time PCR. The expression of genes involved in energy and protein metabolism (F-ATPase, hexokinase and elongation factor alpha) was strongly affected by acclimation to moderately elevated C[O.sub.2] partial pressures. Expression of a chitinase, potentially important for the calcification process, was strongly depressed (maximum ninefold), correlating with a linear decrease in shell growth observed in the experimental animals. Interestingly, shell matrix protein candidate genes were less affected by C[O.sub.2] in both tissues. A compensatory process toward enhanced shell protection is indicated by a massive increase in the expression of tyrosinase, a gene involved in periostracum formation (maximum 220-fold). Using correlation matrices and a force-directed layout network graph, we were able to uncover possible underlying regulatory networks and the connections between different pathways, thereby providing a molecular basis of observed changes in animal physiology in response to ocean acidification., Introduction Ongoing C[O.sub.2]-induced ocean acidification threatens marine ecosystems (Doney et al. 2009). In the eutrophic Western Baltic Sea, ocean acidification is accompanied by seasonal upwelling of C[O.sub.2]-enriched water masses, resulting [...]

Changes in seawater carbonate chemistry that accompany ongoing ocean acidification have been found to affect calcification processes in many marine invertebrates. In contrast to the response of most invertebrates, calcification rates increase in the cephalopod Sepia officinalis during long-term exposure to elevated seawater pCO.sub.2. The present trial investigated structural changes in the cuttlebones of S. officinalis calcified during 6 weeks of exposure to 615 Pa CO.sub.2. Cuttlebone mass increased sevenfold over the course of the growth trail, reaching a mean value of 0.71 ± 0.15 g. Depending on cuttlefish size (mantle lengths 44-56 mm), cuttlebones of CO.sub.2-incubated individuals accreted 22-55% more CaCO.sub.3 compared to controls at 64 Pa CO.sub.2. However, the height of the CO.sub.2-exposed cuttlebones was reduced. A decrease in spacing of the cuttlebone lamellae, from 384 ± 26 to 195 ± 38 [mu]m, accounted for the height reduction The greater CaCO.sub.3 content of the CO.sub.2-incubated cuttlebones can be attributed to an increase in thickness of the lamellar and pillar walls. Particularly, pillar thickness increased from 2.6 ± 0.6 to 4.9 ± 2.2 [mu]m. Interestingly, the incorporation of non-acid-soluble organic matrix (chitin) in the cuttlebones of CO.sub.2-exposed individuals was reduced by 30% on average. The apparent robustness of calcification processes in S. officinalis, and other powerful ion regulators such as decapod cructaceans, during exposure to elevated pCO.sub.2 is predicated to be closely connected to the increased extracellular [HCO.sub.3.sup.-] maintained by these organisms to compensate extracellular pH. The potential negative impact of increased calcification in the cuttlebone of S. officinalis is discussed with regard to its function as a lightweight and highly porous buoyancy regulation device. Further studies working with lower seawater pCO.sub.2 values are necessary to evaluate if the observed phenomenon is of ecological relevance., Author(s): Magdalena A. Gutowska [sup.1] [sup.4] , Frank Melzner [sup.2] , Hans O. Pörtner [sup.1] , Sebastian Meier [sup.3] Author Affiliations: (1) grid.10894.34, 0000000110337684, Alfred-Wegener-Institute for Polar and Marine Research, [...]

Changes in seawater carbonate chemistry that accompany ongoing ocean acidification have been found to affect calcification processes in many marine invertebrates. In contrast to the response of most invertebrates, calcification rates increase in the cephalopod Sepia officinalis during long-term exposure to elevated seawater pCO2. The present trial investigated structural changes in the cuttlebones of S. officinalis calcified during 6 weeks of exposure to 615 Pa CO2. Cuttlebone mass increased sevenfold over the course of the growth trail, reaching a mean value of 0.71 ± 0.15 g. Depending on cuttlefish size (mantle lengths 44–56 mm), cuttlebones of CO2-incubated individuals accreted 22–55% more CaCO3 compared to controls at 64 Pa CO2. However, the height of the CO2-exposed cuttlebones was reduced. A decrease in spacing of the cuttlebone lamellae, from 384 ± 26 to 195 ± 38 μm, accounted for the height reduction The greater CaCO3 content of the CO2-incubated cuttlebones can be attributed to an increase in thickness of the lamellar and pillar walls. Particularly, pillar thickness increased from 2.6 ± 0.6 to 4.9 ± 2.2 μm. Interestingly, the incorporation of non-acid-soluble organic matrix (chitin) in the cuttlebones of CO2-exposed individuals was reduced by 30% on average. The apparent robustness of calcification processes in S. officinalis, and other powerful ion regulators such as decapod cructaceans, during exposure to elevated pCO2 is predicated to be closely connected to the increased extracellular [HCO3 −] maintained by these organisms to compensate extracellular pH. The potential negative impact of increased calcification in the cuttlebone of S. officinalis is discussed with regard to its function as a lightweight and highly porous buoyancy regulation device. Further studies working with lower seawater pCO2 values are necessary to evaluate if the observed phenomenon is of ecological relevance. [ABSTRACT FROM AUTHOR]

Low pO2 values have been measured in the perivitelline fluids (PVF) of marine animal eggs on several occasions, especially towards the end of development, when embryonic oxygen consumption is at its peak and the egg case acts as a massive barrier to diffusion. Several authors have therefore suggested that oxygen availability is the key factor leading to hatching. However, there have been no measurements of PVF pCO2 so far. This is surprising, as elevated pCO2 could also constitute a major abiotic stressor for the developing embryo. As a first attempt to fill this gap in knowledge, we measured pO2, pCO2 and pH in the PVF of late cephalopod ( Sepia officinalis) eggs. We found linear relationships between embryo wet mass and pO2, pCO2 and pH. pO2 declined from >12 kPa to less than 5 kPa, while pCO2 increased from 0.13 to 0.41 kPa. In the absence of active accumulation of bicarbonate in the PVF, pH decreased from 7.7 to 7.2. Our study supports the idea that oxygen becomes limiting in cephalopod eggs towards the end of development; however, pCO2 and pH shift to levels that have caused significant physiological disturbances in other marine ectothermic animals. Future research needs to address the physiological adaptations that enable the embryo to cope with the adverse abiotic conditions in their egg environment. [ABSTRACT FROM AUTHOR]

Low pO2 values have been measured in the perivitelline fluids (PVF) of marine animal eggs on several occasions, especially towards the end of development, when embryonic oxygen consumption is at its peak and the egg case acts as a massive barrier to diffusion. Several authors have therefore suggested that oxygen availability is the key factor leading to hatching. However, there have been no measurements of PVF pCO2 so far. This is surprising, as elevated pCO2 could also constitute a major abiotic stressor for the developing embryo. As a first attempt to fill this gap in knowledge, we measured pO2, pCO2 and pH in the PVF of late cephalopod ( Sepia officinalis) eggs. We found linear relationships between embryo wet mass and pO2, pCO2 and pH. pO2 declined from >12 kPa to less than 5 kPa, while pCO2 increased from 0.13 to 0.41 kPa. In the absence of active accumulation of bicarbonate in the PVF, pH decreased from 7.7 to 7.2. Our study supports the idea that oxygen becomes limiting in cephalopod eggs towards the end of development; however, pCO2 and pH shift to levels that have caused significant physiological disturbances in other marine ectothermic animals. Future research needs to address the physiological adaptations that enable the embryo to cope with the adverse abiotic conditions in their egg environment. [ABSTRACT FROM AUTHOR]