Gill tissue masses and oxygen consumption of Gobionotothen gibberifrons, Notothenia coriiceps and Zoarces viviparus

Mechanisms responsive to hypercapnia (elevated CO2 concentrations) and shaping branchial energy turnover were investigated in isolated perfused gills of two Antarctic Notothenioids (Gobionotothen gibberifrons, Notothenia coriiceps). Branchial oxygen consumption was measured under normo- versus hypercapnic conditions (10,000 ppm CO2) at high extracellular pH values. The fractional costs of ion regulation, protein and RNA synthesis in the energy budgets were determined using specific inhibitors. Overall gill energy turnover was maintained under pH compensated hypercapnia in both Antarctic species as well as in a temperate zoarcid (Zoarces viviparus). However, fractional energy consumption by the examined processes rose drastically in G. gibberifrons (100-180%), and to a lesser extent in N. coriiceps gills (7-56%). In conclusion, high CO2 concentrations under conditions of compensated acidosis induce cost increments in epithelial processes, however, at maintained overall rates of branchial energy turnover.

Impact of ocean acidification and warming on respiration, heart rate and acid-base status of Mytilus edulis from the North Sea

Anthropogenic climate change confronts marine organisms with rapid trends of concomitant warming and CO2 induced ocean acidification. The survival and distribution of species partly depend on their ability to exploit their physiological plasticity during acclimatization. Therefore, in laboratory studies the effects of simulated future ocean acidification on thermal tolerance, energy metabolism and acid-base regulation capacity of the North Sea population of the blue mussel Mytilus edulis were examined. Following one month of pre-acclimation to 10 °C and control CO2 levels, mussels were exposed for two weeks to control and projected oceanic CO2 levels (390, 750 and 1120 µatm) before being subjected to a stepwise warming protocol between 10 °C and 31 °C (+ 3 °C each night). Oxygen consumption and heart rates, anaerobic metabolite levels and haemolymph acid-base status were determined at each temperature. CO2 exposure left oxygen consumption rate unchanged at acclimation temperature but caused a somewhat stronger increase during acute warming and thus mildly higher Q10-values than seen in controls. Interestingly, the thermally induced limitation of oxygen consumption rate set in earlier in normocapnic than in hypercapnic (1120 µatm CO2) mussels (25.2 °C vs. 28.8 °C), likely due to an onset of metabolic depression in the control group following warming. However, the temperature induced increase in heart rate became limited above 25 °C in both groups indicating an unchanged pejus temperature regardless of CO2 treatment. An upper critical temperature was reached above 28 °C in both treatments indicated by the accumulation of anaerobic metabolites in the mantle tissue, paralleled by a strong increase in haemolymph PCO2 at 31 °C. Ocean acidification caused a decrease in haemolymph pH. The extracellular acidosis remained largely uncompensated despite some bicarbonate accumulation. In all treatments animals developed a progressive warming-induced extracellular acidosis. A stronger pH drop at around 25 °C was followed by stagnating heart rates. However, normocapnic mussels enhanced bicarbonate accumulation at the critical limit, a strategy no longer available to hypercapnic mussels. In conclusion, CO2 has small effects on the response patterns of mussels to warming, leaving thermal thresholds largely unaffected. High resilience of adult North Sea mussels to future ocean acidification indicates that sensitivity to thermal stress is more relevant in shaping the response to future climate change.

Environmental characteristics, and growth traits and leaf chemistry of tundra plants in a warming experiment at Alexandra Fiord

Understanding plant trait responses to elevated temperatures in the Arctic is critical in light of recent and continuing climate change, especially because these traits act as key mechanisms in climate-vegetation feedbacks. Since 1992, we have artificially warmed three plant communities at Alexandra Fiord, Nunavut, Canada (79°N). In each of the communities, we used open-top chambers (OTCs) to passively warm vegetation by 1-2 °C. In the summer of 2008, we investigated the intraspecific trait responses of five key species to 16 years of continuous warming. We examined eight traits that quantify different aspects of plant performance: leaf size, specific leaf area (SLA), leaf dry matter content (LDMC), plant height, leaf carbon concentration, leaf nitrogen concentration, leaf carbon isotope discrimination (LCID), and leaf d15N. Long-term artificial warming affected five traits, including at least one trait in every species studied. The evergreen shrub Cassiope tetragona responded most frequently (increased leaf size and plant height/decreased SLA, leaf carbon concentration, and LCID), followed by the deciduous shrub Salix arctica (increased leaf size and plant height/decreased SLA) and the evergreen shrub Dryas integrifolia (increased leaf size and plant height/decreased LCID), the forb Oxyria digyna (increased leaf size and plant height), and the sedge Eriophorum angustifolium spp. triste (decreased leaf carbon concentration). Warming did not affect d15N, leaf nitrogen concentration, or LDMC. Overall, growth traits were more sensitive to warming than leaf chemistry traits. Notably, we found that responses to warming were sustained, even after many years of treatment. Our work suggests that tundra plants in the High Arctic will show a multifaceted response to warming, often including taller shoots with larger leaves.

Community structure and biodiversity in marine benthic communities during experiments, 2011

A mesocosm experiment was conducted to quantify the effects of reduced pH and elevated temperature on an intact marine invertebrate community. Standardised faunal communities, collected from the extreme low intertidal zone using artificial substrate units, were exposed to one of eight nominal treatments (four pH levels: 8.0, 7.7, 7.3 and 6.7, crossed with two temperature levels: 12 and 16°C). After 60 days exposure communities showed significant changes in structure and lower diversity in response to reduced pH. The response to temperature was more complex. At higher pH levels (8.0 and 7.7) elevated temperature treatments contained higher species abundances and diversity than the lower temperature treatments. In contrast, at lower pH levels (7.3 and 6.7), elevated temperature treatments had lower species abundances and diversity than lower temperature treatments. The species losses responsible for these changes in community structure and diversity were not randomly distributed across the different phyla examined. Molluscs showed the greatest reduction in abundance and diversity in response to low pH and elevated temperature, whilst annelid abundance and diversity was mostly unaffected by low pH and was higher at the elevated temperature. The arthropod response was between these two extremes with moderately reduced abundance and diversity at low pH and elevated temperature. Nematode abundance increased in response to low pH and elevated temperature, probably due to the reduction of ecological constraints, such as predation and competition, caused by a decrease in macrofaunal abundance. This community-based mesocosm study supports previous suggestions, based on observations of direct physiological impacts, that ocean acidification induced changes in marine biodiversity will be driven by differential vulnerability within and between different taxonomical groups. This study also illustrates the importance of considering indirect effects that occur within multispecies assemblages when attempting to predict the consequences of ocean acidification and global warming on marine communities.

Rare earth element contents in deposits and minerals of the ocean floor

Current understanding of rare earth element (REE) geochemistry in the ocean is given in the book. Chemical properties determining REE migration ability in natural processes, sources of REE in the ocean, behavior of REE in river-sea mixing zones, fractionation of dissolved and particulate REE in ocean waters under aerobic and anaerobic conditions, distribution of REE in terrigenous, authigenic, hydrothermal and biogenic sediment components (clay, bone detritus, barite, phillipsite, Fe- and Mn-oxyhydroxides, Fe-Ca hydroxophosphate, diatoms and foraminiferas) are under consideration.

Seawater carbonate chemistry and zooxanthellate coral Cladocora caespitosa boron isotopic and elemental systematics during experiments, 2011

Boron isotopic and elemental systematics are used to define the vital effects for the temperate shallow water Mediterranean coral Cladocora caespitosa. The corals are from a range of seawater pH conditions (pHT ~ 7.6 to ~ 8.1) and environmental settings: (1) naturally living colonies harvested from normal pH waters offshore Levanto, (2) colonies transplanted nearby a subsea volcanic vent system, and (3) corals cultured in aquaria exposed to high (700 µatm) and near present day (400 µatm) pCO2 levels. B/Ca compositions measured using laser ablation inductively coupled mass spectrometry (LA-ICPMS) show that boron uptake by C. caespitosa cultured at different pCO2 levels is independent of ambient seawater pH being mainly controlled by temperature-dependent calcification. In contrast, the boron isotope compositions (delta11Bcarb) of the full suite of corals determined by positive thermal ionisation mass spectrometry (PTIMS) shows a clear trend of decreasing delta11Bcarb (from 26.7 to 22.2 %o) with decreasing seawater pH, reflecting the strong pH dependence of the boron isotope system. The delta11Bcarb compositions together with measurements of ambient seawater parameters enable calibration of the boron pH proxy for C. caespitosa, by using a new approach that defines the relationship between ambient seawater pH (pHsw) and the internally controlled pH at the site of calcification (pHbiol). C. caespitosa exhibits a linear relationship between pHsw and the shift in pH due to physiological processes (deltapH = pHbiol - pHsw) giving the regression deltapHClad = 4.80 - 0.52* pHsw for this species. We further apply this method ("deltapH-pHsw") to calibrate tropical species of Porites, Acropora, and Stylophora reported in the literature. The temperate and tropical species calibrations are all linearly correlated (r2 > 0.9) and the biological fractionation component (deltapH) between species varies within ~ 0.2 pH units. Our "deltapH-pHsw" approach provides a robust and accurate tool to reconstruct palaeoseawater pHsw for both temperate and tropical corals, further validating the boron fractionation factor (alphaB3-B4 = 1.0272) determined experimentally by Klochko et al. (2006) and the boron isotope pH proxy, both of which have been the foci of considerable debate.

Chemical versus structural defense against fish predation in two dominant soft coral species (Xeniidae) in the Red Sea

Soft corals of the family Xeniidae are particularly abundant in Red Sea coral reefs. Their success may be partly due to a strong defense mechanism against fish predation. To test this, we conducted field and aquarium experiments in which we assessed the antifeeding effect of secondary metabolites of 2 common xeniid species, Ovabunda crenata and Heteroxenia ghardaqensis. In the field experiment, the metabolites of both investigated species reduced feeding on experimental food pellets in the natural population of Red Sea reef fishes by 86 and 92% for O. crenata and H. ghardaqensis, respectively. In the aquarium experiment, natural concentration of crude extract reduced feeding on experimental food pellets in the common reef fish Thalassoma lunare (moon wrasse) by 83 and 85%, respectively. Moon wrasse feeding was even reduced at extract concentrations as low as 12.5% of the natural concentration in living soft coral tissues. To assess the potential of a structural anti-feeding defence, sclerites of O. crenata were extracted and mixed into food pellets at natural, doubled and reduced concentration without and in combination with crude extract at 25% of natural concentration, and tested in an aquarium experiment. The sclerites did not show any effect on the feeding behavior of the moon wrasse indicating that sclerites provide structural support rather than antifeeding defense. H. ghardaqensis lacks sclerites. We conclude that the conspicuous abundance of xeniid soft coral species in the Red Sea is likely a consequence of a strong chemical defence, rather than physical defences, against potential predators.