Long photoperiods sustain high pH in Arctic kelp forests

Concern on the impacts of ocean acidification on calcifiers, such as bivalves, sea urchins, and foraminifers, has led to efforts to understand the controls on pH in their habitats, which include kelp forests and seagrass meadows. The metabolism of these habitats can lead to diel fluctuation in pH with increases during the day and declines at night, suggesting no net effect on pH at time scales longer than daily. We examined the capacity of subarctic and Arctic kelps to up-regulate pH in situ and experimentally tested the role of photoperiod in determining the capacity of Arctic macrophytes to up-regulate pH. Field observations at photoperiods of 15 and 24 hours in Greenland combined with experimental manipulations of photoperiod show that photoperiods longer than 21 hours, characteristic of Arctic summers, are conducive to sustained up-regulation of pH by kelp photosynthesis. We report a gradual increase in pH of 0.15 units and a parallel decline in pCO2 of 100 parts per million over a 10-day period in an Arctic kelp forest over midsummer, with ample scope for continued pH increase during the months of continuous daylight. Experimental increase in CO2 concentration further stimulated the capacity of macrophytes to deplete CO2 and increase pH. We conclude that long photoperiods in Arctic summers support sustained up-regulation of pH in kelp forests, with potential benefits for calcifiers, and propose that this mechanism may increase with the projected expansion of Arctic vegetation in response to warming and loss of sea ice.The study was funded by the Danish Environmental Protection Agency within the Danish Cooperation for Environment in the Arctic. It is also a contribution to the Greenland Ecosystem Monitoring program (www.G-E-M.dk) and the Arctic Science Partnership (www.asp-net.org). M.S.-M. was supported by a Fundación “La Caixa” fellowship (Spain). We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe

Canopy-Forming Macroalgae Facilitate Recolonization of Sub-Arctic Intertidal Fauna and Reduce Temperature Extremes

Ice can be an important structuring factor physically removing intertidal flora and fauna. At high latitudes in particular, the removal of canopy-forming algae by ice scour may be important as their canopy may serve to modify the extreme environment for marine organisms at low tide. We simulated the effect of ice scouring by manipulating the biomass of the canopy-forming algae Ascophyllum nodosum in a sub-Arctic fjord [“Full canopy,” “Reduced canopy,” “Bare (start),” “Bare (annual)”]. Over a three-year period, we quantified key physical parameters and the recolonization of flora and fauna to test the hypothesis that A. nodosum and rock rugosity facilitate recolonization of sub-Arctic intertidal fauna and that potential facilitation could rely on an ability of A. nodosum canopy to modify air temperature and ice scour. Finally, we estimated the recovery period of A. nodosum canopy height to pre-disturbance levels based on estimated early growth rates. We found that A. nodosum canopy facilitated higher species richness and recolonization of dominating faunal species (Littorina saxatilis, Littorina obtusata, Mytilus edulis, and Semibalanus balanoides), and also significantly reduced the high temperatures in summer and raised the low temperatures in winter. The abundance of M. edulis and A. nodosum recolonization increased significantly with rock rugosity and the recovery of A. nodosum canopy height was estimated to a minimum of 15 years. We conclude that algal canopy and rock rugosity play key roles in structuring sub-Arctic intertidal communities, likely by modifying environmental stress such as extreme temperature, desiccation, and by increasing the settling surface and the habitat complexity. As the distribution of canopy-forming algae is expected to shift northward, they may act as a key habitat facilitating a northward colonization of intertidal fauna in the Arctic. We highlight the importance of considering scales relevant to biological communities when predicting impacts of climate change on distributional patterns and community structure in the Arctic intertidal

Thrombus aspiration during ST-segment elevation myocardial infarction.

To access publisher's full text version of this article. Please click on the hyperlink in Additional Links field.The clinical effect of routine intracoronary thrombus aspiration before primary percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI) is uncertain. We aimed to evaluate whether thrombus aspiration reduces mortality.We conducted a multicenter, prospective, randomized, controlled, open-label clinical trial, with enrollment of patients from the national comprehensive Swedish Coronary Angiography and Angioplasty Registry (SCAAR) and end points evaluated through national registries. A total of 7244 patients with STEMI undergoing PCI were randomly assigned to manual thrombus aspiration followed by PCI or to PCI only. The primary end point was all-cause mortality at 30 days.No patients were lost to follow-up. Death from any cause occurred in 2.8% of the patients in the thrombus-aspiration group (103 of 3621), as compared with 3.0% in the PCI-only group (110 of 3623) (hazard ratio, 0.94; 95% confidence interval [CI], 0.72 to 1.22; P=0.63). The rates of hospitalization for recurrent myocardial infarction at 30 days were 0.5% and 0.9% in the two groups, respectively (hazard ratio, 0.61; 95% CI, 0.34 to 1.07; P=0.09), and the rates of stent thrombosis were 0.2% and 0.5%, respectively (hazard ratio, 0.47; 95% CI, 0.20 to 1.02; P=0.06). There were no significant differences between the groups with respect to the rate of stroke or neurologic complications at the time of discharge (P=0.87). The results were consistent across all major prespecified subgroups, including subgroups defined according to thrombus burden and coronary flow before PCI.Routine thrombus aspiration before PCI as compared with PCI alone did not reduce 30-day mortality among patients with STEMI. (Funded by the Swedish Research Council and others; ClinicalTrials.gov number, NCT01093404.).Swedish Research Council, Swedish Association of Local Authorities and Regions, Terumo Medical Corporation, Medtronic, Vascular Solutions, Swedish Heart-Lung Foundation/20100178/ B0010401 Biotronik, Stentys, Abbott Vascular, St. Jude Medical, Boston Scientific, EPS Vascular, Cardiac Dimensions, AstraZeneca, Edwards Lifesciences

Food supply confers calcifiers resistance to ocean acidification

Invasion of ocean surface waters by anthropogenic CO emitted to the atmosphere is expected to reduce surface seawater pH to 7.8 by the end of this century compromising marine calcifiers. A broad range of biological and mineralogical mechanisms allow marine calcifiers to cope with ocean acidification, however these mechanisms are energetically demanding which affect other biological processes (trade-offs) with important implications for the resilience of the organisms against stressful conditions. Hence, food availability may play a critical role in determining the resistance of calcifiers to OA. Here we show, based on a meta-analysis of existing experimental results assessing the role of food supply in the response of organisms to OA, that food supply consistently confers calcifiers resistance to ocean acidification.This work was funded by grants from the Danish Environmental Protection Agency within the Danish 486 Cooperation for Environment in the Arctic (DANCEA), ASSEMBLE grant agreement no. 227799 from European Community and from the Spanish Ministry of Economy and Competitiveness (ESTRESX, number CTM2012-32603). N.A.L. acknowledges support from grants Fondecyt 1140938 and NC 1200286 (Millennium Nucleus Project MUSELS) and L.R. was supported by BECAS CHILE fellowship program from Comisión Nacional de Investigación Científica y Tecnológica de Chile (CONICYT)Peer Reviewe

Tying Up a Loose End: On the Role of the C‐Terminal CCHHRAG Fragment of the Metalloregulator CueR

The transcriptional regulator CueR is activated by the binding of CuI, AgI, or AuI to two cysteinates in a near-linear fashion. The C-terminal CCHHRAG sequence in Escherichia coli CueR present potential additional metal binding ligands and here we explore the effect of deleting this fragment on the binding of AgI to CueR. CD spectroscopic and ESI-MS data indicate that the high AgI-binding affinity of WT-CueR is significantly reduced in Δ7C-CueR.[111 Ag PAC spectroscopy demonstrates that the WT-CueR metal site structure (AgS2) is conserved, but less populated in the truncated variant. Thus, the function of the C-terminal fragment may be to stabilize the two-coordinate metal site for cognate monovalent metal ions. In a broader perspective this is an example of residues beyond the second coordination sphere affecting metal site physicochemical properties while leaving the structure unperturbed