The mechanism of action of a novel benzo[c]phenanthridine alkaloid, NK314 and the cellular responses

NK314 is a novel synthetic benzo[c]phenanthridine alkaloid that is currently in clinical trials as an antitumor compound, based on impressive activities in preclinical models. However, its mechanism of action is unknown. The present investigations were directed at determining the mechanism of action of this agent and cellular responses to NK314. My studies demonstrated that NK314 intercalated into DNA, trapped topoisomerase IIα in its cleavage complex intermediate, and inhibited the ability of topoisomerase IIα to relax super-coiled DNA. CEM/VM1 cells, which are resistant to etoposide due to mutations in topoisomerase IIα, were cross-resistant to NK314. However, CEM/C2 cells, which are resistant to camptothecin due to mutations in topoisomerase I, retained sensitivity. This indicates topoisomerase IIα is the target of NK314 in the cells. NK314 caused phosphorylation of the histone variant, H2AX, which is considered a marker of DNA double-strand breaks. DNA double-strand breaks were also evidenced by pulsed-field gel electrophoresis and visualized as chromosomal aberrations after cells were treated with NK314 and arrested in mitosis. Cell cycle checkpoints are activated following DNA damage. NK314 induced significant G2 cell cycle arrest in several cell lines, independent of p53 status, suggesting the existence of a common mechanism of checkpoint activation. The Chk1-Cdc25C-Cdk1 G2 checkpoint pathway was activated in response to NK314, which can be abrogated by the Chk1 inhibitor UCN-01. Cell cycle checkpoint activation may be a defensive mechanism that provides time for DNA repair. DNA double-strand breaks are repaired either through ATM-mediated homologous recombination or DNA-PK-mediated non-homologous end-joining repair pathways. Clonogenic assays demonstrated a significant decrease of colony formation in both ATM deficient and DNA-PK deficient cells compared to ATM repleted and DNA-PK wild type cells respectively, indicating that both ATM and DNA-PK play important roles in the survival of the cells in response to NK314. The DNA-PK specific inhibitor NU7441 also significantly sensitized cells to NK314. In conclusion, the major mechanism of NK314 is to intercalate into DNA, trap and inhibit topoisomerase IIα, an action that leads to the generation of double-strand DNA breaks, which activate ATM and DNA-PK mediated DNA repair pathways and Chk1 mediated G2 checkpoint pathway. ^

Role of telomere dysfunction, DNA damage response and p53 mutations in tumorigenesis and aging

The ends of eukaryotic chromosomes are protected by specialized ribonucleoprotein structures termed telomeres. Telomeres protect chromosomes from end-to-end fusions, inappropriate repair and degradation. Disruption of this complex activates an ATM/ATR DNA damage response (DDR) pathway. One component of the complex is the Protection Of Telomeres 1 (POT1) protein, an evolutionarily conserved protein which binds single-stranded 3' overhang and is required for both chromosomal end protection and telomere length regulation. The mouse contains two POT1 orthologs, Pot1a and Pot1b. Here we show that both proteins colocalize with telomeres through interaction with the adapter protein TPP1. In addition, compared to Pot1a, the OB-folds of Pot1b possess less sequence specificity for telomeres. Disruption of POT1 proteins result in telomere dysfunction and activation of an ATR-dependent DDR at telomeres, suggesting that this response is normally suppressed by POT1 binding to the single-stranded G-overhang. ^ Telomeres are maintained by telomerase, and its absence in somatic cells results in telomere progressive loss that triggers the activation of p53. Telomere dysfunction initiates genomic instability and induces both p53-dependent replicative senescence and apoptosis to suppress tumorigenesis. In the absence of functional p53, this genomic instability promotes cancer. It was previously not known which aspect of the p53 dependent DNA damage response is important to suppress tumorigenesis initiated by dysfunctional telomeres. The p53R172P knock-in mouse, which is unable to induce apoptosis but retains intact cell cycle arrest/cellular senescence pathways, allowed us to examine whether p53-dependent apoptosis is a major tumor suppression pathway initiated in the setting of telomere dysfunction. Spontaneous tumorigenesis remains potently suppressed in late generation telomerase null mice possessing the p53P/P mutation. These results suggest that suppression of spontaneous tumorigenesis initiated by dysfunctional telomeres requires activation of a p53-dependent senescence pathway. In addition, we used another knock-in mouse model with a p53R172H (p53H) point mutation to test the hypothesis that telomere dysfunction promotes chromosomal instability and accelerates the onset of tumorigenesis in vivo in the setting of this most common gain-of-function mutation in the human Li Fraumeni cancer syndrome. We unexpectedly observed that telomerase null mice possessing dysfunctional telomeres in the setting of the p53H/+ mutation develop significantly fewer tumors, die prematurely and exhibit higher level of cellular senescence, apoptosis and elevated genomic instability compared to telomerase intact p53H/+ and telomerase null p53+/+ mice. These contrasting results thus link cancer and aging to the functional status of telomeres and the integrity of the p53 pathway. ^

Emerging roles for the double strand break repair protein 53BP1 in transcriptional regulation

Disruption of the mechanisms that regulate cell-cycle checkpoints, DNA repair, and apoptosis results in genomic instability and often leads to the development of cancer. In response to double stranded breaks (DSBs) as induced by ionizing radiation (IR), generated during DNA replication, or through immunoglobulin heavy chain (IgH) rearrangements in T and B cells of lymphoid origin, the protein kinases ATM and ATR are central players that activate signaling pathways leading to DSB repair. p53 binding protein 1 (53BP1) participates in the repair of DNA double stranded breaks (DSBs) where it is recruited to or near sites of DNA damage. In addition to its well established role in DSB repair, multiple lines of evidence implicate 53BP1 in transcription which stem from its initial discovery as a p53 binding protein in a yeast two-hybrid screen. However, the mechanisms behind the role of 53BP1 in these processes are not well understood. ^ 53BP1 possesses several motifs that are likely important for its role in DSB repair including two BRCA1 C-terminal repeats, tandem Tudor domains, and a variety of phosphorylation sites. In addition to these motifs, we identified a glycine and arginine rich region (GAR) upstream of the Tudor domains, a sequence that is oftentimes serves as a site for protein arginine methylation. The focus of this project was to characterize the methylation of 53BP1 and to evaluate how methylation influenced the role of 53BP1 as a tumor suppressor. ^ Using a variety of biochemical techniques, we demonstrated that 53BP1 is methylated by the PRMT1 methyltransferase in vivo. Moreover, GAR methylation occurs on arginine residues in an asymmetric manner. We further show that sequences upstream of the Tudor domains that do not include the GAR stretch are sufficient for 53BP1 oligomerization in vivo. While investigating the role of arginine methylation in 53BP1 function, we discovered that 53BP1 associates with proteins of the general transcription apparatus as well as to other factors implicated in coordinating transcription with chromatin function. Collectively, these data support a role for 53BP1 in regulating transcription and provide insight into the possible mechanisms by which this occurs. ^

The cellular and molecular responses to a novel nucleotide analogue, GS-9219

GS-9219 is a cell-permeable double-prodrug of the acyclic nucleotide analogue 9-(2-phosphonylmethoxyethyl)guanine (PMEG). The conversion of GS-9219 to its active metabolite, PMEG diphosphate (PMEGpp), involves several intracellular enzymatic reactions which reduces the concentration of nephrotoxic PMEG in plasma. PMEGpp competes with the natural substrate, dGTP, for incorporation by DNA polymerases. The lack of a 3'-hydroxyl moiety makes PMEGpp a de facto DNA chain-terminator. The incorporation of PMEGpp into DNA during DNA replication causes DNA chain-termination and stalled replication forks. Thus, the primary mechanism of action of GS-9219 in replicating cells is via DNA synthesis inhibition. GS-9219 has substantial antiproliferative activity against activated lymphocytes and tumor cell lines of hematological malignancies. Tumor cell proliferation was significantly reduced as measured by PET/CT scans in dogs with advanced-stage, spontaneously occurring non-Hodgkin's lymphoma (NHL).^ The hypothesis of this dissertation is that the incorporation of PMEGpp into DNA during repair re-synthesis would result in the inhibition of DNA repair and accumulation of DNA damage in chronic lymphocytic leukemia (CLL) cells and activate signaling pathways to cell death.^ To test this hypothesis, CLL cells were treated with DNA-damaging agents to stimulate nucleotide excision repair (NER) pathways, enabling the incorporation of PMEGpp into DNA. When NER was activated by UV, PMEGpp was incorporated into DNA in CLL cells. Following PMEGpp incorporation, DNA repair was inhibited and led to the accumulation of DNA strand breaks. The combination of GS-9219 and DNA-damaging agents resulted in more cell death than the sum of the single agents alone. The presence of DNA strand breaks activated the phosphatidylinositol 3-kinase-like protein kinase (PIKK) family members ataxia-telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNA-PK). The activated ATM initiated signaling to the downstream target, p53, which was subsequently phosphorylated and accumulated to exert its apoptotic functions. P53-targeted pro-apoptotic genes, Puma and Bax, were upregulated and activated when DNA repair was inhibited, likely contributing to cell death. ^

E2F1's role in ultraviolet-induced DNA damage response

The E2F1 transcription factor is a well-known regulator of cell proliferation and apoptosis, but its role in the DNA damage response is less clear. It has been shown that E2F1 becomes stabilized in response to DNA double strand breaks (DSBs) and accumulates at sites of DSBs. This process requires ATM kinase and serine 31 phosphorylation, which provides a binding site for TopBp1. However, the role of E2F1 at sites of DNA damage is not clear. We expanded the study of E2F1's role in the DNA damage response by exploring its functions in ultraviolet (UV) induced DNA damage, and identified that E2F1 promotes DNA repair and cell survival. To further investigate the mechanisms underlying our findings, we examined the possibility for direct involvement of E2F1 in DNA repair. We found that E2F1 localizes to sites of UV irradiation-induced DNA damage dependent on the ATR kinase and serine 31 of E2F1. E2F1 also associates with the GCN5 histone acetyltransferase in response to UV irradiation and recruits GCN5 to sites of DNA damage. This correlates with an increase in histone H3 lysine 9 (H3K9) acetylation and chromatin relaxation. In the absence of E2F1 or GCN5, nucleotide excision repair (NER) proteins do not efficiently localize to sites of UV damage and DNA repair is impaired. E2F1 mutants unable to bind DNA or activate transcription retain the ability to stimulate NER. These findings demonstrate a non-transcriptional role for E2F1 in DNA repair involving GCN5-mediated H3K9 acetylation and increased accessibility to the NER machinery. ^

Using K5 Myc transgenic mice to delineate *Myc's apoptotic and tumorigenic pathways

The c-myc oncogene has the unusual ability to induce proliferation and apoptosis. Transgenic mice have been generated in which the expression of Myc is under the control of an epithelial-specific keratin 5 (K5) promoter. These mice have increased levels of proliferation and p53-dependent apoptosis, and are predisposed to developing spontaneous tumors in epithelial tissues. In this study, various knockout mice were bred to K5 Myc transgenic mice to identify factors involved in the aberrant apoptosis, hyperproliferation, and spontaneous tumorigenesis present in these mice. Consistent with in vitro studies, Myc-induced, p53-dependent apoptosis in transgenic epidermis was found to be partially dependent on p19ARF, a p53 regulator that inhibits mdm2. Additionally, the rate of tumorigenesis was increased when p19ARF was absent in Myc transgenic mice. Consistent with previous reports that some E2F family members may function as tumor suppressors, inactivation of either E2f1 or E2f2 was found to accelerate tumor development in the K5 Myc transgenic mice. Acceleration of tumorigenesis in the absence of E2F1 occurred despite the fact that apoptotic levels were increased in transgenic tissue and tumors null for E2f1 , whereas hyperproliferation was unaffected. In contrast, inactivation of E2f2 was found to increase hyperproliferation in the K5 Myc transgenic mice, while having no effect on apoptosis. The lack of E2f1 in the Myc transgenic mice increased the expression of several p53 transcription target genes, which may explain the increased apoptosis in these mice. In transgenic epidermis, p53 is phosphorylated at serine 18, a site of phosphorylation by ATM. Inactivation of ATM in K5 Myc transgenic mice impaired Myc-induced apoptosis, identifying ATM as having an important role in Myc-induced apoptosis. Moreover, the absence of ATM accelerates tumorigenesis in K5-expressing tissues. However, p53 accumulation and phosphorylation at serine 18 induced by Myc occurs independent of ATM. Therefore, another activity of ATM appears to be important for Myc-induced apoptosis. These findings show that acceleration of tumorigenesis in K5 Myc transgenic mice, as in the case of p53, p19ARF, E2F1, E2F2, and ATM absence, does not necessarily correlate with suppression of Myc-induced apoptosis, as seen only when p53, p19ARF or ATM was absent. ^

Effects of increased CO2 concentration on nutrient limited coastal summer plankton depend on temperature

Increasing seawater temperature and CO2 concentrations both are expected to increase coastal phytoplankton biomass and carbon to nutrient ratios in nutrient limited seasonally stratified summer conditions. This is because temperature enhances phytoplankton growth while grazing is suggested to be reduced during such bottom-up controlled situations. In addition, enhanced CO2 concentrations potentially favor phytoplankton species, that otherwise depend on costly carbon concentrating mechanisms (CCM). The trophic consequences for consumers under such conditions, however, remain little understood. We set out to experimentally explore the combined effects of increasing temperature and CO2 concentration for phytoplankton biomass and stoichiometry and the consequences for trophic transfer (here for copepods) on a natural nutrient limited Baltic Sea summer plankton community. The results show, that warming effects were translated to the next trophic level by switching the system from a bottom-up controlled to a mainly top-down controlled one. This was reflected in significantly down-grazed phytoplankton and increased zooplankton abundance in the warm temperature treatment (22.5°C). Additionally, at low temperature (16.5°C) rising CO2 concentrations significantly increased phytoplankton biomass. The latter effect however, was due to direct negative impact of CO2 on copepod nauplii which released phytoplankton from grazing in the cold but not in the warm treatments. Our results suggest that future seawater warming has the potential to switch trophic relations between phytoplankton and their grazers under nutrient limited conditions with the consequence of potentially disguising CO2 effects on coastal phytoplankton biomass.

Transferencia de un fondo de comercio como aporte para la constitución de sociedad comercial

Una de las competencias de un contador, según la ley 20.488 de ejercicio profesional, art. 13, inciso 9, es intervenir en las operaciones de transferencia de fondos de comercio sin perjuicio de las facultades reservadas a otros profesionales en la ley 11.867. Cualquier transferencia de un fondo de comercio y en especial cuando se trata de su aporte para constituir una sociedad, es una operación compleja dado que requiere dar cumplimiento a un conjunto de normas legales y además implica la realización de trámites ante la Dirección de Personas Jurídicas de Mendoza (DPJ), la Administración Federal de Ingresos Públicos (AFIP), la Dirección de Registros Públicos y Archivo Judicial, la Administración Tributaria Mendoza - Dirección General de Rentas de Mendoza (ATM - DGR), el Boletín Oficial de Mendoza (BO), la Subsecretaría de Trabajo y Seguridad Social de Mendoza (STySS) y la Municipalidad que corresponda al departamento donde se encuentra el fondo de comercio. Los objetivos principales de este trabajo son: 1. Brindar un resumen sobre los principales conceptos teóricos relativos a una transferencia de fondo de comercio: concepto, naturaleza jurídica y elementos de un fondo de comercio; intereses protegidos por la ley 11.867. 2. Estudiar el aporte societario de un fondo de comercio, teniendo en cuenta, la normativa societaria, comercial, impositiva, previsional y laboral. 3. Desarrollar en forma cronológica, las distintas etapas a cumplir para llevar a cabo el aporte societario de un fondo de comercio dando cumplimiento a todas las disposiciones legales y reglamentarias.

Atmospheric and seawater carbon dioxide at time series station DYFAMED

A time series of fCO2, SST, and fluorescence data was collected between 1995 and 1997 by a CARIOCA buoy moored at the DyFAMed station (Dynamique des Flux Atmospheriques en Mediterranée) located in the northwestern Mediterranean Sea. On seasonal timescales, the spring phytoplankton bloom decreases the surface water fCO2 to approximately 290 µatm, followed by summer heating and a strong increase in fCO2 to a maximum of approximately 510 µatm. While the DELTA fCO2 shows strong variations on seasonal timescales, the annual average air-sea disequilibrium is only 2 µatm. Temperature-normalized fCO2 shows a continued decrease in dissolved CO2 throughout the summer and fall at a rate of approximately 0.6 µatm/d. The calculated annual air-sea CO2 transfer rate is -0.10 to -0.15 moles CO2 m-2 y-1, with these low values reflecting the relatively weak wind speed regime and small annual air-sea fCO2 disequilibrium. Extrapolating this rate over the whole Mediterranean Sea would lead to a flux of approximately -3 * 10**12 to -4.5 * 10**12 grams C/y, in good agreement with other estimates. An analysis of the effects of sampling frequency on annual air-sea CO2 flux estimates showed that monthly sampling is adequate to resolve the annual CO2 flux to within approximately ±10 - 18% at this site. Annual flux estimates made using temperature-derived fCO2 based on the measured fCO2-SST correlations are in agreement with measurement-based calculations to within ± 7-10% (depending on the gas transfer parameterization used), and suggest that annual CO2 flux estimates may be reasonably well predicted in this region from satellite or model-derived SST and wind speed information.

Crustal uplift rates of 4 GPS stations near Jakobshavn Isbrae (2006-2009)

We analyze 2006-2009 data from four continuous Global Positioning System (GPS) receivers located between 5 and 150 km from the glacier Jakobshavn Isbrae, West Greenland. The GPS stations were established on bedrock to determine the vertical crustal motion due to the unloading of ice from Jakobshavn Isbrae. All stations experienced uplift, but the uplift rate at Kangia North, only 5 km from the glacier front, was about 10 mm/yr larger than the rate at Ilulissat, located only ~45 km further away. This suggests that most of the uplift is due to the unloading of the Earth's surface as Jakobshavn thins and loses mass. Our estimate of Jakobshavn's contribution to uplift rates at Kangia North and Ilulissat are 14.6 ± 1.7 mm/yr and 4.9 ± 1.1 mm/yr, respectively. The observed rates are consistent with a glacier thinning model based on repeat altimeter surveys from NASA's Airborne Topographic Mapper (ATM), which shows that Jakobshavn lost mass at an average rate of 22 ± 2 km**3/yr between 2006 and 2009. At Kangia North and Ilulissat, the predicted uplift rates computed using thinning estimates from the ATM laser altimetry are 12.1 ± 0.9 mm/yr and 3.2 ± 0.3 mm/yr, respectively. The observed rates are slightly larger than the predicted rates. The fact that the GPS uplift rates are much larger closer to Jakobshavn than further away, and are consistent with rates inferred using the ATM-based glacier thinning model, shows that GPS measurements of crustal motion are a potentially useful method for assessing ice-mass change models.

(Table 3) Run conditions and phase relations and proportions during cooling rate experiments on ODP Interval 163-989B-10R-7,55-59

Equilibrium melting and controlled cooling experiments were undertaken to constrain the crystallization and cooling histories of tholeiitic basalts recovered by the Ocean Drilling Program drilling of Site 989 on the Southeast Greenland continental margin. Isothermal experiments conducted at 1 atm. and at the fayalite-magnetite-quartz buffer using lava sample Section 163-989B-10R-7 yielded the equilibrium appearance sequence with decreasing temperature: olivine at 1184 ± 2ºC; plagioclase at 1177ºC ± 5ºC; augite at 1167 ± 5ºC; and pigeonite at 1113 ± 12ºC. In controlled cooling experiments using the same starting composition and cooling rates between 10ºC/hr and 2000ºC/hr, we find a significant temperature delay in the crystallization of olivine, plagioclase, and augite (relative to the equilibrium appearance temperature); pigeonite does not form under any dynamic crystallization conditions. Olivine exhibits the largest suppression in appearance temperature (e.g., 30º for 10ºC/hr and >190º at 100ºC/hr), while plagioclase shows the smallest (~10ºC at 10ºC/hr; 30ºC at 100ºC/hr, and ~80ºC at 1000ºC/hr). These results are in marked contrast to those obtained on lunar basalts, which generally show a large suppression of plagioclase crystallization and modest suppression of olivine crystallization with an increased cooling rate. The results we report agree well with the petrography of lavas recovered from Site 989. Furthermore, the textural analysis of run products, representing a large range of cooling rates and quench temperatures (1150ºC to 1000ºC), provide a framework for evaluating cooling conditions necessary for glass formation, rates of plagioclase growth, and kinetic factors governing plagioclase growth morphology. Specifically, we use these insights to interpret the textural and mineralogical features of the unusual compound flow recovered at Site 989. We concluded from the analysis that this flow most likely records multiple breakouts from a distal tube at an abrupt break in slope, possibly a fault scarp, resulting in the formation of a lava fan delta. This interpretation implies that normal faulting of the oldest lava sequences (lower and, possibly, middle series) preceded eruption of Site 989 lavas.

Seawater carbonate chemistry and calcification rate in flume experiment

Ocean acidification (OA) poses a severe threat to tropical coral reefs, yet much of what is know about these effects comes from individual corals and algae incubated in isolation under high pCO2. Studies of similar effects on coral reef communities are scarce. To investigate the response of coral reef communities to OA, we used large outdoor flumes in which communities composed of calcified algae, corals, and sediment were combined to match the percentage cover of benthic communities in the shallow back reef of Moorea, French Polynesia. Reef communities in the flumes were exposed to ambient (400 ?atm) and high pCO2 (1300 ?atm) for 8 weeks, and calcification rates measured for the constructed communities including the sediments. Community calcification was reduced by 59% under high pCO2, with sediment dissolution explaining ~ 50% of this decrease; net calcification of corals and calcified algae remained positive but was reduced by 29% under elevated pCO2. These results show that, despite the capacity of coral reef calcifiers to maintain positive net accretion of calcium carbonate under OA conditions, reef communities might transition to net dissolution as pCO2 increases, particularly at night, due to enhanced sediment dissolution.

Biotic and abiotic parameters and cynobacteria abundance during an experimental set-up with varying pCO2 conditions

Heterocystous cyanobacteria of the genus Nodularia form extensive blooms in the Baltic Sea and contribute substantially to the total annual primary production. Moreover, they dispense a large fraction of new nitrogen to the ecosystem when inorganic nitrogen concentration in summer is low. Thus, it is of ecological importance to know how Nodularia will react to future environmental changes, in particular to increasing carbon dioxide (CO2) concentrations and what consequences there might arise for cycling of organic matter in the Baltic Sea. Here, we determined carbon (C) and dinitrogen (N2) fixation rates, growth, elemental stoichiometry of particulate organic matter and nitrogen turnover in batch cultures of the heterocystous cyanobacterium Nodularia spumigena under low (median 315 µatm), mid (median 353 µatm), and high (median 548 µatm) CO2 concentrations. Our results demonstrate an overall stimulating effect of rising pCO2 on C and N2 fixation, as well as on cell growth. An increase in pCO2 during incubation days 0 to 9 resulted in an elevation in growth rate by 84 ± 38% (low vs. high pCO2) and 40 ± 25% (mid vs. high pCO2), as well as in N2 fixation by 93 ± 35% and 38 ± 1%, respectively. C uptake rates showed high standard deviations within treatments and in between sampling days. Nevertheless, C fixation in the high pCO2 treatment was elevated compared to the other two treatments by 97% (high vs. low) and 44% (high vs. mid) at day 0 and day 3, but this effect diminished afterwards. Additionally, elevation in carbon to nitrogen and nitrogen to phosphorus ratios of the particulate biomass formed (POC : POP and PON : POP) was observed at high pCO2. Our findings suggest that rising pCO2 stimulates the growth of heterocystous diazotrophic cyanobacteria, in a similar way as reported for the non-heterocystous diazotroph Trichodesmium. Implications for biogeochemical cycling and food web dynamics, as well as ecological and socio-economical aspects in the Baltic Sea are discussed.

Limacina helicina size weight relationship in Kongsfjorden Svalbard, May 2009

Thecosome pteropods (pelagic mollusks) can play a key role in the food web of various marine ecosystems. They are a food source for zooplankton or higher predators such as fishes, whales and birds that is particularly important in high latitude areas. Since they harbor a highly soluble aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO2 emissions. The effect of changes in the seawater chemistry was investigated on Limacina helicina, a key species of Arctic pelagic ecosystems. Individuals were kept in the laboratory under controlled pCO2 levels of 280, 380, 550, 760 and 1020 µatm and at control (0°C) and elevated (4°C) temperatures. The respiration rate was unaffected by pCO2 at control temperature, but significantly increased as a function of the pCO2 level at elevated temperature. pCO2 had no effect on the gut clearance rate at either temperature. Precipitation of CaCO3, measured as the incorporation of 45Ca, significantly declined as a function of pCO2 at both temperatures. The decrease in calcium carbonate precipitation was highly correlated to the aragonite saturation state. Even though this study demonstrates that pteropods are able to precipitate calcium carbonate at low aragonite saturation state, the results support the current concern for the future of Arctic pteropods, as the production of their shell appears to be very sensitive to decreased pH. A decline of pteropod populations would likely cause dramatic changes to various pelagic ecosystems.

Colony-specific investigations reveal highly variable responses among individual corals to ocean acidification and warming

As anthropogenic climate change is an ongoing concern, scientific investigations on its impacts on coral reefs are increasing. Although impacts of combined ocean acidification (OA) and temperature stress (T) on reef-building scleractinian corals have been studied at the genus, species and population levels, there are little data available on how individual corals respond to combined OA and anomalous temperatures. In this study, we exposed individual colonies of Acropora digitifera, Montipora digitata and Porites cylindrica to four pCO2-temperature treatments including 400 µatm-28 °C, 400 µatm-31 °C, 1000 µatm-28 °C and 1000 µatm-31 °C for 26 days. Physiological parameters including calcification, protein content, maximum photosynthetic efficiency, Symbiodinium density, and chlorophyll content along with Symbiodinium type of each colony were examined. Along with intercolonial responses, responses of individual colonies versus pooled data to the treatments were investigated. The main results were: 1) responses to either OA or T or their combination were different between individual colonies when considering physiological functions; 2) tolerance to either OA or T was not synonymous with tolerance to the other parameter; 3) tolerance to both OA and T did not necessarily lead to tolerance of OA and T combined (OAT) at the same time; 4) OAT had negative, positive or no impacts on physiological functions of coral colonies; and 5) pooled data were not representative of responses of all individual colonies. Indeed, the pooled data obscured actual responses of individual colonies or presented a response that was not observed in any individual. From the results of this study we recommend improving experimental designs of studies investigating physiological responses of corals to climate change by complementing them with colony-specific examinations.