Molecular Responses to Thermal and Osmotic Stress in Arctic Intertidal Mussels (Mytilus edulis): The Limits of Resilience.

Increases in Arctic temperatures have accelerated melting of the Greenland icesheet, exposing intertidal organisms, such as the blue mussel Mytilus edulis, to high air temperatures and low salinities in summer. However, the interaction of these combined stressors is poorly described at the transcriptional level. Comparing expression profiles of M. edulis from experimentally warmed (30 °C and 33 °C) animals kept at control (23‱) and low salinities (15‱) revealed a significant lack of enrichment for Gene Ontology terms (GO), indicating that similar processes were active under all conditions. However, there was a progressive increase in the abundance of upregulated genes as each stressor was applied, with synergistic increases at 33 °C and 15‱, suggesting combined stressors push the animal towards their tolerance thresholds. Further analyses comparing the effects of salinity alone (23‱, 15‱ and 5‱) showed high expression of stress and osmoregulatory marker genes at the lowest salinity, implying that the cell is carrying out intracellular osmoregulation to maintain the cytosol as hyperosmotic. Identification of aquaporins and vacuolar-type ATPase transcripts suggested the cell may use fluid-filled cavities to excrete excess intracellular water, as previously identified in embryonic freshwater mussels. These results indicate that M. edulis has considerable resilience to heat stress and highly efficient mechanisms to acclimatise to lowered salinity in a changing world

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

Supplementary Data and Codes: "Blue mussel shell shape plasticity and natural environments: a quantitative approach"

These dataset contain supplementary data and codes supporting the morphometrics and statistical analyses for the publication entitled “Blue mussel shell shape plasticity and natural environments: a quantitative approach”: 1) Raw data (.rda, 3 files) for geometric morphometrics analyses with the Momocs (Bonhomme et al. 2014, J Stat Softw, DOI: 10.18637/jss.v056.i13) package with the R software; 2) Raw morphometrics data (.txt, 7 files) for morphometrics and statistical analyses; 3) Reports of R scripts and codes (.pdf, 4 files) in R-markdown format; 4) Supporting R script with utility codes (.R format, 1 file); 5) Description file providing additional information on data and codes included (.pdf, 1 file). Data were collected as part of the EU Marie Curie programme, Calcium in a Changing Environment – Initial Training Networks (CACHE-ITN)

Long photoperiods sustain high pH in Arctic kelp forests Dataset

The data is displayed in an excel file with spreadsheets representing each of the following data sets: Field kelp loggings Nuuk, Field kelp loggings Disko, Field ETR Disko, Lab time series pH CO2, Lab CO2 End time series, Lab time series consumption CO2, Lab ETR max and Lab time series no macroph. The txt document attached provides a full description of each of them.This dataset contains field- and laboratory data of metabolic activity, photosynthetic characteristics and associated effects on water chemistry of Greenland kelp forests. Field data include diurnal variation in pH, pCO2, O2-concentration, light, temperature, and salinity in shallow kelp forests habitats over 10-day periods in the subarctic Kobbefjord (64⁰N, 51⁰W) in late summer 2013 at a photoperiod of 15 h light and in the Arctic Disko Bay (69 °N, 53 °W) during midsummer 2014 at a photoperiod of 24 h light. Field data further include in-situ measurements of photosynthetic activity (relative electron transport rate, rETR) during a diurnal cycle in midsummer in Disko Bay. Laboratory data include time series of seawater pH, CO2 concentration and rates of change of CO2 concentration and photosynthetic activity of arctic vegetation measured during experimental manipulations of photoperiod and CO2 concentration in aquaria at 4 oC. There were three replicated aquaria per CO2 concentration treatment (200 ppm, 400 ppm and 1000 ppm). Each aquarium contained 6 L of artificial seawater and 2.7 – 3.7 gDW of macrophytes (Ascophyllum nodosum, Fucus vesiculosus, Saccharina longicruris, Zostera marina) collected at Nuuk. Methods are described in detail in Krause-Jensen et al. (2016).The study was funded by the Danish Environmental Protection Agency within the Danish Cooperation for Environment in the Arctic (DANCEA). It is also a contribution to the Greenland Ecosystem Monitoring program (www.G-E-M.dk) and to the Arctic Science Partnership (www.asp-net.org). M.S-M. was supported by a Fundación “La Caixa” fellowship (ES).Peer reviewe

Acute oil exposure reduces physiological process rates in Arctic phyto- and zooplankton

Arctic shipping and oil exploration are expected to increase, as sea ice extent is reduced. This enhances the risk for accidental oil spills throughout the Arctic, which emphasises the need to quantify potential consequences to the marine ecosystem and to evaluate risk and choose appropriate remediation methods. This study investigated the sensitivity of Arctic marine plankton to the water accommodated fraction (WAF) of heavy fuel oil. Arctic marine phytoplankton and copepods (Calanus finmarchicus) were exposed to three WAF concentrations corresponding to total hydrocarbon contents of 0.07 mg l−1, 0.28 mg l−1 and 0.55 mg l−1. Additionally, the potential phototoxic effects of exposing the WAF to sunlight, including the UV spectrum, were tested. The study determined sub-lethal effects of WAF exposure on rates of key ecosystem processes: primary production of phytoplankton and grazing (faecal pellet production) of copepods. Both phytoplankton and copepods responded negatively to WAF exposure. Biomass specific primary production was reduced by 6, 52 and 73% and faecal pellet production by 18, 51 and 86% with increasing WAF concentrations compared to controls. The phototoxic effect reduced primary production in the two highest WAF concentration treatments by 71 and 91%, respectively. This experiment contributes to the limited knowledge of acute sub-lethal effects of potential oil spills to the Arctic pelagic food web