Impacts of seawater acidification on mantle gene expression patterns of the Baltic Sea blue mussel: implications for shell formation and energy metabolism, link to supplementary material

Marine organisms have to cope with increasing CO2 partial pressures and decreasing pH in the oceans. We elucidated the impacts of an 8-week acclimation period to four seawater pCO2 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 CO2 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 CO2 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.

Localization of ion-regulatory epithelia in embryos and hatchlings of two cephalopods

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 alpha (H-300) raised against the human alpha1-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/g FM/h) than in those of L. vulgaris (31.8 ± 3.3 µmol/g FM/h). S. officinalis gills and pancreatic appendages achieved activities of 94.8 ± 18.5 and 421.8 ± 102.3 µmol ATP/g FM/h, 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.

Data compilation on the biological response to ocean acidification: environmental and experimental context of data sets and related literature

The exponential growth of studies on the biological response to ocean acidification over the last few decades has generated a large amount of data. To facilitate data comparison, a data compilation hosted at the data publisher PANGAEA was initiated in 2008 and is updated on a regular basis (doi:10.1594/PANGAEA.149999). By January 2015, a total of 581 data sets (over 4 000 000 data points) from 539 papers had been archived. Here we present the developments of this data compilation five years since its first description by Nisumaa et al. (2010). Most of study sites from which data archived are still in the Northern Hemisphere and the number of archived data from studies from the Southern Hemisphere and polar oceans are still relatively low. Data from 60 studies that investigated the response of a mix of organisms or natural communities were all added after 2010, indicating a welcomed shift from the study of individual organisms to communities and ecosystems. The initial imbalance of considerably more data archived on calcification and primary production than on other processes has improved. There is also a clear tendency towards more data archived from multifactorial studies after 2010. For easier and more effective access to ocean acidification data, the ocean acidification community is strongly encouraged to contribute to the data archiving effort, and help develop standard vocabularies describing the variables and define best practices for archiving ocean acidification data.

Experiment: Acidified seawater impacts sea urchin larvae pH regulatory systems relevant for calcification

Calcifying echinoid larvae respond to changes in seawater carbonate chemistry with reduced growth and developmental delay. To date, no information exists on how ocean acidification acts on pH homeostasis in echinoderm larvae. Understanding acid-base regulatory capacities is important because intracellular formation and maintenance of the calcium carbonate skeleton is dependent on pH homeostasis. Using H(+)-selective microelectrodes and the pH-sensitive fluorescent dye BCECF, we conducted in vivo measurements of extracellular and intracellular pH (pH(e) and pH(i)) in echinoderm larvae. We exposed pluteus larvae to a range of seawater CO(2) conditions and demonstrated that the extracellular compartment surrounding the calcifying primary mesenchyme cells (PMCs) conforms to the surrounding seawater with respect to pH during exposure to elevated seawater pCO(2). Using FITC dextran conjugates, we demonstrate that sea urchin larvae have a leaky integument. PMCs and spicules are therefore directly exposed to strong changes in pH(e) whenever seawater pH changes. However, measurements of pH(i) demonstrated that PMCs are able to fully compensate an induced intracellular acidosis. This was highly dependent on Na(+) and HCO(3)(-), suggesting a bicarbonate buffer mechanism involving secondary active Na(+)-dependent membrane transport proteins. We suggest that, under ocean acidification, maintained pH(i) enables calcification to proceed despite decreased pH(e). However, this probably causes enhanced costs. Increased costs for calcification or cellular homeostasis can be one of the main factors leading to modifications in energy partitioning, which then impacts growth and, ultimately, results in increased mortality of echinoid larvae during the pelagic life stage.

Seawater carbonate chemistry and biological processes of Sepia officinalis during experiments, 2010

Acidification of ocean surface waters by anthropogenic carbon dioxide (CO2) emissions is a currently developing scenario that warrants a broadening of research foci in the study of acid-base physiology. Recent studies working with environmentally relevant CO2 levels, indicate that some echinoderms and molluscs reduce metabolic rates, soft tissue growth and calcification during hypercapnic exposure. In contrast to all prior invertebrate species studied so far, growth trials with the cuttlefish Sepia officinalis found no indication of reduced growth or calcification performance during long-term exposure to 0.6 kPa CO2. It is hypothesized that the differing sensitivities to elevated seawater pCO2 could be explained by taxa specific differences in acid-base regulatory capacity. In this study, we examined the acid-base regulatory ability of S. officinalis in vivo, using a specially modified cannulation technique as well as 31P NMR spectroscopy. During acute exposure to 0.6 kPa CO2, S. officinalis rapidly increased its blood [HCO3] to 10.4 mM through active ion-transport processes, and partially compensated the hypercapnia induced respiratory acidosis. A minor decrease in intracellular pH (pHi) and stable intracellular phosphagen levels indicated efficient pHi regulation. We conclude that S. officinalis is not only an efficient acid-base regulator, but is also able to do so without disturbing metabolic equilibria in characteristic tissues or compromising aerobic capacities. The cuttlefish did not exhibit acute intolerance to hypercapnia that has been hypothesized for more active cephalopod species (squid). Even though blood pH (pHe) remained 0.18 pH units below control values, arterial O2 saturation was not compromised in S. officinalis because of the comparatively lower pH sensitivity of oxygen binding to its blood pigment. This raises questions concerning the potentially broad range of sensitivity to changes in acid-base status amongst invertebrates, as well as to the underlying mechanistic origins. Further studies are needed to better characterize the connection between acid-base status and animal fitness in various marine species.