ALBERT

Description: Marine teleost fish sustain compensation of extracellular pH after exposure to hypercapnia by means of efficient ion and acid-base regulation. Elevated rates of ion and acid-base regulation under hypercapnia may be stimulated further by elevated temperature. Here, we characterized the regulation of transepithelial ion transporters (NKCC1, NBC1, SLC26A6, NHE1 and 2) and ATPases (Na(+)/K(+) ATPase and V-type H(+) ATPase) in gills of Atlantic cod (Gadus morhua) after 4 weeks of exposure to ambient and future PCO2 levels (550 μatm, 1200 μatm, 2200 μatm) at optimum (10 °C) and summer maximum temperature (18 °C), respectively. Gene expression of most branchial ion transporters revealed temperature- and dose-dependent responses to elevated PCO2. Transcriptional regulation resulted in stable protein expression at 10 °C, whereas expression of most transport proteins increased at medium PCO2 and 18 °C. mRNA and protein expression of distinct ion transport proteins were closely co-regulated, substantiating cellular functional relationships. Na(+)/K(+) ATPase capacities were PCO2 independent, but increased with acclimation temperature, whereas H(+) ATPase capacities were thermally compensated but decreased at medium PCO2 and 10 °C. When functional capacities of branchial ATPases were compared with mitochondrial F1Fo ATP-synthase strong correlations of F1Fo ATP-synthase and ATPase capacities generally indicate close coordination of branchial aerobic ATP demand and supply. Our data indicate physiological plasticity in the gills of cod to adjust to a warming, acidifying ocean within limits. In light of the interacting and non-linear, dose-dependent effects of both climate factors the role of these mechanisms in shaping resilience under climate change remains to be explored.

Description: Understanding mollusk calcification sensitivity to ocean acidification (OA) requires a better knowledge of calcification mechanisms. Especially in rapidly calcifying larval stages, mechanisms of shell formation are largely unexplored—yet these are the most vulnerable life stages. Here we find rapid generation of crystalline shell material in mussel larvae. We find no evidence for intracellular CaCO3 formation, indicating that mineral formation could be constrained to the calcifying space beneath the shell. Using microelectrodes we show that larvae can increase pH and [CO32−] beneath the growing shell, leading to a ~1.5-fold elevation in calcium carbonate saturation state (Ωarag). Larvae exposed to OA exhibit a drop in pH, [CO32−] and Ωarag at the site of calcification, which correlates with decreased shell growth, and, eventually, shell dissolution. Our findings help explain why bivalve larvae can form shells under moderate acidification scenarios and provide a direct link between ocean carbonate chemistry and larval calcification rate.

Description: The unusual rate and extent of environmental changes due to human activities may exceed the capacity of marine organisms to deal with this phenomenon. The identification of physiological systems that set the tolerance limits and their potential for phenotypic buffering in the most vulnerable ontogenetic stages become increasingly important to make large-scale projections. Here, we demonstrate that the differential sensitivity of non-calcifyingAmbulacraria (echinoderms and hemichordates) larvae towards simulated ocean acidification is dictated by the physiology of their digestive systems. Gastric pH regulation upon experimental ocean acidification was compared in six species of the superphylum Ambulacraria.We observed a strong correlation between sensitivity to ocean acidification and the ability to regulate gut pH. Surprisingly, species with tightly regulated gastric pH were more sensitive to ocean acidification. This study provides evidence that strict maintenance of highly alkaline conditions in the larval gut of Ambulacraria early life stages may dictate their sensitivity to decreases in seawater pH. These findings highlight the importance of identifying and understanding pH regulatory systems in marine larval stages that may contribute to substantial energetic challenges under near-future ocean acidification scenarios.

Description: Occan acidification due to anthropogenic emissions of CO, is the rew kid on the block of climate change research and has received considerable attention as changes in seawater acidity and carbonate chemistry caa severely affect marine organisms from the species to the ecosystem level. The degree of sensitivity within a species can vary greatly aloeg ontogeny. olVr leading to highest sensitivities .n early life stages Recent ssadies using the cuttlefish Septa officinalis, demonstrated that it's oviparous developmental mode can constitute an additional dulSenge for early life stages as increases in environmental pCO, add on top lo the already high COj concentration irtiide the egg The nucnxnvironment inside the egg is characterized by low pH. hypoxia, hypercapnia and high ammonia concentrations as a result of the animal's metabolism and the limited diffusion permeability of the egg capsule. This oviparous developmental mode ia combination with tower pH regulatory capacities are probably the major reasons why S officinalis embryo∗ respond more sensitively towards seanater acidification compared to adalts Although stronger hypercapnia levels (〉0.3 kPa; 〈 pH 75) could demonstrate potentially negative effects on the development, metabolism and calcification, acidification levels as predicted for the coming century will probably not severely affect S. officinalis. This relative tolerance may be a consequence of a lifestyle in benthac coastal habitats, pre- Adapiiag S. officinalis to natural fluctuations in environmental. Effects of C02 driven ocean acidification on ontogenetic stages of the cutllefisii SEPIA OFFICINALIS (PDF Download Available). Available from: https://www.researchgate.net/publication/304749386_Effects_of_C02_driven_ocean_acidification_on_ontogenetic_stages_of_the_cutllefisii_SEPIA_OFFICINALIS [accessed Jan 10 2018].

Description: Ocean acidification is an escalating environmental issue and associated changes in the ocean carbonate system have implications for many calcifying organisms. The present study followed the growth of Sepia officinalis from early-stage embryos, through hatching, to 7-week-old juveniles. Responses of cuttlefish to elevated pCO(2) (hypercapnia) were investigated to test the impacts of near-future and extreme ocean acidification conditions on growth, developmental time, oxygen consumption, and yolk utilization as proxies for individual fitness. We further examined gross morphological characteristics of the internal calcareous cuttlebone to determine whether embryonically secreted shell lamellae are impacted by environmental hypercapnia. Embryonic growth was reduced and hatching delayed under elevated pCO(2), both at environmentally relevant levels (0.14 kPa pCO(2) similar to predicted ocean conditions in 2100) and extreme conditions (0.40 kPa pCO(2)). Comparing various metrics from control and intermediate treatments generally showed no significant difference in experimental measurements. Yet, results from the high pCO(2) treatment showed significant changes compared with controls and revealed a consistent general trend across the three treatment levels. The proportion of animal mass contributed by the cuttlebone increased in both elevated pCO(2) treatments. Gross cuttlebone morphology was affected under such conditions and cuttlebones of hypercapnic individuals were proportionally shorter. Embryonic shell morphology was maintained consistently in all treatments, despite compounding hypercapnia in the perivitelline fluid; however, post-hatching, hypercapnic animals developed denser cuttlebone laminae in shorter cuttlebones. Juvenile cuttlefish in acidified environments thus experience lower growth and yet increased calcification of their internal shell. The results of this study support recent findings that early cuttlefish life stages are more vulnerable towards hypercapnia than juveniles and adults, which may have negative repercussions on the biological fitness of cuttlefish hatchlings in future oceans.

Description: The tissue distribution and ontogeny of Na+/K+-ATPase has been examined as an indicator for ion-regulatory epithelia in whole animal sections of embryos and hatchlings of two cephalopod species: the squid Loligo vulgaris and the cuttlefish Sepia officinalis. This is the first report of the immunohistochemical localization of cephalopod Na+/K+-ATPase with the polyclonal antibody α (H-300) raised against the human α1-subunit of Na+/K+-ATPase. Na+/K+-ATPase immunoreactivity was observed in several tissues (gills, pancreatic appendages, nerves), exclusively located in baso-lateral membranes lining blood sinuses. Furthermore, large single cells in the gill of adult L. vulgaris specimens closely resembled Na+/K+-ATPase-rich cells described in fish. Immunohistochemical observations indicated that the amount and distribution of Na+/K+-ATPase in late cuttlefish embryos was similar to that found in juvenile and adult stages. The ion-regulatory epithelia (e.g., gills, excretory organs) of the squid embryos and paralarvae exhibited less differentiation than adults. Na+/K+-ATPase activities for whole animals were higher in hatchlings of S. officinalis (157.0 ± 32.4 µmol gFM−1 h−1) than in those of L. vulgaris (31.8 ± 3.3 µmol gFM−1 h−1). S. officinalis gills and pancreatic appendages achieved activities of 94.8 ± 18.5 and 421.8 ± 102.3 µmolATP gFM−1 h−1, respectively. High concentrations of Na+/K+-ATPase in late cephalopod embryos might be important in coping with the challenging abiotic conditions (low pH, high pCO2) that these organisms encounter inside their eggs. Our results also suggest a higher sensitivity of squid vs. cuttlefish embryos to environmental acid-base disturbances.

Description: The stomachs of most vertebrates operate at an acidic pH of 2 generated by the gastric H+/K+-ATPase located in parietal cells. The acidic pH in stomachs of vertebrates is believed to aid digestion and to protect against environmental pathogens. Little attention has been placed on whether acidic gastric pH regulation is a vertebrate character or a deuterostome ancestral trait. Here, we report alkaline conditions up to pH 10.5 in the larval digestive systems of ambulacraria (echinoderm + hemichordate), the closest relative of the chordate. Microelectrode measurements in combination with specific inhibitors for acid-base transporters and ion pumps demonstrated that the gastric alkalization machinery in sea urchin larvae is mainly based on direct H+ secretion from the stomach lumen and involves a conserved set of ion pumps and transporters. Hemichordate larvae additionally utilized HCO 3- transport pathways to generate even more alkaline digestive conditions. Molecular analyses in combination with acidification experiments supported these findings and identified genes coding for ion pumps energizing gastric alkalization. Given that insect larval guts were also reported to be alkaline, our discovery raises the hypothesis that the bilaterian ancestor utilized alkaline digestive system while the vertebrate lineage has evolved a strategy to strongly acidify their stomachs.