Ocean acidification and temperature increase impact mussel shell shape and thickness: problematic for protection?

Ocean acidification threatens organisms that produce calcium carbonate shells by potentially generating an under‐saturated carbonate environment. Resultant reduced calcification and growth, and subsequent dissolution of exoskeletons, would raise concerns over the ability of the shell to provide protection for the marine organism under ocean acidification and increased temperatures. We examined the impact of combined ocean acidification and temperature increase on shell formation of the economically important edible mussel Mytilus edulis. Shell growth and thickness along with a shell thickness index and shape analysis were determined. The ability of M. edulis to produce a functional protective shell after 9 months of experimental culture under ocean acidification and increasing temperatures (380, 550, 750, 1000 μatm pCO ₂, and 750, 1000 μatm pCO ₂ + 2°C) was assessed. Mussel shells grown under ocean acidification conditions displayed significant reductions in shell aragonite thickness, shell thickness index, and changes to shell shape (750, 1000 μatm pCO ₂) compared to those shells grown under ambient conditions (380 μatm pCO ₂). Ocean acidification resulted in rounder, flatter mussel shells with thinner aragonite layers likely to be more vulnerable to fracture under changing environments and predation. The changes in shape presented here could present a compensatory mechanism to enhance protection against predators and changing environments under ocean acidification when mussels are unable to grow thicker shells. Here, we present the first assessment of mussel shell shape to determine implications for functional protection under ocean acidification.     

Sponge bioerosion accelerated by ocean acidification across species and latitudes?

In many marine biogeographic realms, bioeroding sponges dominate the internal bioerosion of calcareous substrates such as mollusc beds and coral reef framework. They biochemically dissolve part of the carbonate and liberate so-called sponge chips, a process that is expected to be facilitated and accelerated in a more acidic environment inherent to the present global change. The bioerosion capacity of the demosponge Cliona celata Grant, 1826 in subfossil oyster shells was assessed via alkalinity anomaly technique based on 4 days of experimental exposure to three different levels of carbon dioxide partial pressure (pCO₂) at ambient temperature in the cold-temperate waters of Helgoland Island, North Sea. The rate of chemical bioerosion at present-day pCO₂ was quantified with 0.08–0.1 kg m^?2 year^?1. Chemical bioerosion was positively correlated with increasing pCO₂, with rates more than doubling at carbon dioxide levels predicted for the end of the twenty-first century, clearly confirming that C. celata bioerosion can be expected to be enhanced with progressing ocean acidification (OA). Together with previously published experimental evidence, the present results suggest that OA accelerates sponge bioerosion (1) across latitudes and biogeographic areas, (2) independent of sponge growth form, and (3) for species with or without photosymbionts alike. A general increase in sponge bioerosion with advancing OA can be expected to have a significant impact on global carbonate (re)cycling and may result in widespread negative effects, e.g. on the stability of wild and farmed shellfish populations, as well as calcareous framework builders in tropical and cold-water coral reef ecosystems.     

Host–parasite interactions: a litmus test for ocean acidification?

The effects of ocean acidification (OA) on marine species and ecosystems have received significant scientific attention in the past 10 years. However, to date, the effects of OA on host-parasite interactions have been largely ignored. As parasites play a multidimensional role in the regulation of marine population, community, and ecosystem dynamics, this knowledge gap may result in an incomplete understanding of the consequences of OA. In addition, the impact of stressors associated with OA on host-parasite interactions may serve as an indicator of future changes to the biodiversity of marine systems. This opinion article discusses the potential effects of OA on host and parasite species and proposes the use of parasites as bioindicators of OA disturbance.     

Dispersal and divergence across the greatest ocean region: Do larvae matter?

For marine, benthic animals, duration of planktonic larval stagesis expected to correlate with dispersal ability, and thus speciesranges, at least where planktonic dispersal is necessary toreach habitats. Yet past analyses of larval duration and speciesranges across the insular Pacific show at most a weak correlation.So, do larvae matter in determining species ranges in such anisland setting? We analyze an extensive dataset on cowries andfind, again, that estimated larval duration does not correlatewith species ranges. Several factors can obscure a real correlation,however, including estimation error, intraspecific variation,other factors affecting dispersal, poor taxonomy, and remoteendemics. We show that taking these into consideration greatlyimproves correlation. Further evidence for the importance oflarval duration comes from diversity and speciation patterns.Diversity of poor dispersers drops more rapidly eastward acrossthe Pacific and leads to taxonomic differences in communitycomposition across the basin. Geographic scale of differentiationis strongly influenced by larval duration and leads to the mostrapid diversification at intermediate dispersal capacities.A major lesson from the phylogenetically corrected cowrie datasetis that without accurate and appropriate taxonomy, clear andimportant distributional and diversity patterns can become obscured.Inappropriate taxonomic scale can also obscure macroecologicalpatterns: cowrie tribes/subfamilies show substantial variationin the steepness of their diversity cline across the Pacificand in their proportional local abundance, showing the importanceof ecological traits in controlling distributions. In contrastsuch variation was not evident in a study focused at the familylevel in corals and fishes.     

Metabolically induced pH fluctuations by some coastal calcifiers exceed projected 22nd century ocean acidification: a mechanism for differential susceptibility?

Anthropogenically mediated decreases in pH, termed ocean acidification (OA), may be a major threat to marine organisms and communities. Research has focussed mainly on tropical coral reefs, but temperate reefs play a no less important ecological role in colder waters, where OA effects may first be manifest. Herein, we report that trends in pH at the surface of three ecologically important cold‐water calcifiers (a primary producer and herbivores), under a range of fluid flows, differ substantially from one another, and for two of the three calcifiers, the pH, during darkness, is lower than the mean projected pH due to OA for the surface waters of the global ocean beyond the year 2100. Using micro‐electrodes, we show that each calcifier had a different pH gradient between its surface and mainstream seawater, i.e. within the diffusion boundary layer (DBL) that appears to act as an environmental buffer to mainstream pH. Abalone encountered only mainstream seawater pH, whereas pH at the sea urchins’ surface was reduced by ~0.35 units. For coralline algae, pH was ~0.5 units higher in the light and ~0.35 units lower under darkness than in ambient mainstream seawater. This wide range of pH within the DBL of some calcifiers will probably affect their performance under projected future reductions in pH due to OA. Differing exposure to a range of surface pH may result in differential susceptibility of calcifiers to OA. Such fluctuations are no doubt regulated by the interplay of water movement, morphology and metabolic rates (e.g. respiration, calcification and/or photosynthesis). Our study, by considering physics (flow regime), chemistry (pH gradients vs. OA future projections) and biology (trophic level, physiology and morphology), reveals that predicting species‐specific responses and subsequent ecosystem restructuring to OA is complex and requires a holistic, eco‐mechanical, approach.     

Do low oxygen environments facilitate marine invasions? Relative tolerance of native and invasive species to low oxygen conditions

Biological invasions are one of the biggest threats to global biodiversity. Marine artificial structures are proliferating worldwide and provide a haven for marine invasive species. Such structures disrupt local hydrodynamics, which can lead to the formation of oxygen‐depleted microsites. The extent to which native fauna can cope with such low oxygen conditions, and whether invasive species, long associated with artificial structures in flow‐restricted habitats, have adapted to these conditions remains unclear. We measured water flow and oxygen availability in marinas and piers at the scales relevant to sessile marine invertebrates (mm). We then measured the capacity of invasive and native marine invertebrates to maintain metabolic rates under decreasing levels of oxygen using standard laboratory assays. We found that marinas reduce water flow relative to piers, and that local oxygen levels can be zero in low flow conditions. We also found that for species with erect growth forms, invasive species can tolerate much lower levels of oxygen relative to native species. Integrating the field and laboratory data showed that up to 30% of available microhabitats within low flow environments are physiologically stressful for native species, while only 18% of the same habitat is physiologically stressful for invasive species. These results suggest that invasive species have adapted to low oxygen habitats associated with manmade habitats, and artificial structures may be creating niche opportunities for invasive species.     

Do ADHD symptoms moderate the relation between positive alcohol expectancies and alcohol-related outcomes?

Research indicates that attention-deficit/hyperactivity disorder (ADHD) may be a risk factor for heavy alcohol use and related problems. Research also suggests that positive alcohol expectancies (i.e., positive beliefs about the effects of alcohol) are predictive of risky alcohol use and related problems (e.g., driving while intoxicated). However, no research has examined the association between ADHD symptoms and positive expectancies or the role of ADHD symptoms in the relation between positive expectancies and alcohol use and related problems, an unexplored area addressed by the current study. Participants were 889 undergraduates (76 % female, 82.3 % Caucasian) at a Southeastern University who completed self-report measures. Parent report (59 %) of current and childhood ADHD symptoms was also collected. Findings indicated that ADHD symptoms moderated the relation between positive alcohol expectancies and alcohol-related problems, but not the relation between expectancies and alcohol use. Additional analyses revealed that ADHD symptoms moderated the specific relation between positive expectancies and social alcohol problems (e.g., engaging in unplanned sexual behavior), but not between expectancies and internal alcohol problems (e.g., feeling sad). Moderating effects were significant even after controlling for conduct disorder symptoms and stimulant medication use. Findings have implications for the identification of college students who are at particularly high risk for heavy drinking and alcohol-related problems. Results may also aid in the development of interventions aimed at reducing risky drinking among students.     

Can multitrophic interactions and ocean warming influence large‐scale kelp recovery?

Ongoing changes along the northeastern Atlantic coastline provide an opportunity to explore the influence of climate change and multitrophic interactions on the recovery of kelp. Here, vast areas of sea urchin‐dominated barren grounds have shifted back to kelp forests, in parallel with changes in sea temperature and predator abundances. We have compiled data from studies covering more than 1,500‐km coastline in northern Norway. The dataset has been used to identify regional patterns in kelp recovery and sea urchin recruitment, and to relate these to abiotic and biotic factors, including structurally complex substrates functioning as refuge for sea urchins. The study area covers a latitudinal gradient of temperature and different levels of predator pressure from the edible crab (Cancer pagurus) and the red king crab (Paralithodes camtschaticus). The population development of these two sea urchin predators and a possible predator on crabs, the coastal cod (Gadus morhua), were analyzed. In the southernmost and warmest region, kelp forests recovery and sea urchin recruitment are mainly low, although sea urchins might also be locally abundant. Further north, sea urchin barrens still dominate, and juvenile sea urchin densities are high. In the northernmost and cold region, kelp forests are recovering, despite high recruitment and densities of sea urchins. Here, sea urchins were found only in refuge habitats, whereas kelp recovery occurred mainly on open bedrock. The ocean warming, the increase in the abundance of edible crab in the south, and the increase in invasive red king crab in the north may explain the observed changes in kelp recovery and sea urchin distribution. The expansion of both crab species coincided with a population decline in the top‐predator coastal cod. The role of key species (sea urchins, kelp, cod, and crabs) and processes involved in structuring the community are hypothesized in a conceptual model, and the knowledge behind the suggested links and interactions is explored.     

Erythropoietin and the skin: a role for epidermal oxygen sensing?

Erythropoietin (EPO), long appreciated as the chief endocrine regulator of red blood cell formation, is now recognized to exert many additional functions outside the bone marrow. Thus, the quest is on to define the full range of EPO functions in the physiology and pathology of non‐hematopoietic tissues. Two recent studies in man and mice have highlighted the importance of the mammalian skin as one peripheral tissue with a previously unsuspected role in EPO biology; both, as a target and as a source of EPO. In addition, the skin has been proposed to function as an oxygen sensor. The present hypothesis essay critically reviews the currently available evidence for this and provides a unifying theoretical scenario for intracutaneous EPO functions and for a potential role of the skin in the control of EPO production. Mainly, we propose that the skin itself directly contributes to the up‐regulation of EPO plasma levels in response to hypoxia.     

Can novel Apo A-I polymorphisms be responsible for low HDL in South Asian immigrants?

Coronary artery disease (CAD) is the leading cause of death in the world. Even though its rates have decreased worldwide over the past 30 years, event rates are still high in South Asians. South Asians are known to have low high-density lipoprotein (HDL) levels. The objective of this study was to identify Apolipoprotein A-I (Apo A-I) polymorphisms, the main protein component of HDL and explore its association with low HDL levels in South Asians. A pilot study on 30 South Asians was conducted and 12-h fasting samples for C-reactive protein, total cholesterol, HDL, low-density lipoprotein (LDL), triglycerides, Lipoprotein (a), Insulin, glucose levels, DNA extraction, and sequencing of Apo A-I gene were done. DNA sequencing revealed six novel Apo A-I single nucleotide polymorphisms (SNPs) in South Asians, one of which (rs 35293760, C938T) was significantly associated with low (<40 mg/dl) HDL levels (P = 0.004). The association was also seen with total cholesterol (P = 0.026) and LDL levels (P = 0.032). This pilot work has highlighted some of the gene-environment associations that could be responsible for low HDL and may be excess CAD in South Asians. Further larger studies are required to explore and uncover these associations that could be responsible for excess CAD risk in South Asians.     

Luminescence materials for pH and oxygen sensing in microbial cells – structures,optical properties,and biological applications

Luminescence including fluorescence and phosphorescence sensors have been demonstrated to be important for studying cell metabolism, and diagnosing diseases and cancer. Various design principles have been employed for the development of sensors in different formats, such as organic molecules, polymers, polymeric hydrogels, and nanoparticles. The integration of the sensing with fluorescence imaging provides valuable tools for biomedical research and applications at not only bulk-cell level but also at single-cell level. In this article, we critically reviewed recent progresses on pH, oxygen, and dual pH and oxygen sensors specifically for their application in microbial cells. In addition, we focused not only on sensor materials with different chemical structures, but also on design and applications of sensors for better understanding cellular metabolism of microbial cells. Finally, we also provided an outlook for future materials design and key challenges in reaching broad applications in microbial cells.     

Calcification, growth and mortality of juvenile clams Ruditapes decussatus under increased pCO2 and reduced pH: Variable responses to ocean acidification at local scales?

We investigated the effects of ocean acidification on juvenile clams Ruditapes decussatus (average shell length 10.24 mm) in a controlled CO₂ perturbation experiment. The carbonate chemistry of seawater was manipulated by diffusing pure CO₂, to attain two reduced pH levels (by −0.4 and −0.7 pH units), which were compared to unmanipulated seawater. After 75 days we found no differences among pH treatments in terms of net calcification, size or weight of the clams. The naturally elevated total alkalinity of local seawater probably contributed to buffer the effects of increased pCO₂ and reduced pH. Marine organisms may, therefore, show diverse responses to ocean acidification at local scales, particularly in coastal, estuarine and transitional waters, where the physical-chemical characteristics of seawater are most variable. Mortality was significantly reduced in the acidified treatments. This trend was probably related to the occurrence of spontaneous spawning events in the control and intermediate acidification treatments. Spawning, which was unexpected due to the small size of the clams, was not observed for the pH −0.7 treatment, suggesting that the increased survival under acidified conditions may have been associated with a delay in the reproductive cycle of the clams. Future research about the impacts of ocean acidification on marine biodiversity should be extended to other types of biological and ecological processes, apart from biological calcification.     

Feedback between zebra mussel selective feeding and algal composition affects mussel condition: did the regime changer pay a price for its success?

1. We investigated the role of algal composition on pumping, clearance, assimilation, pseudofaeces and faeces production, feeding time budgets, and condition of zebra mussels from spring to autumn at two sites in Saginaw Bay (Lake Huron) and one site in western Lake Erie. Size‐fractioned chlorophyll was used to distinguish between feeding on small (<53 μm) and large (>53 μm) size fractions, and mussel feeding behaviour was quantified by video observations. 2. Mussel pumping, clearance and assimilation rates varied among sites, particularly during summer, when phytoplankton composition varied considerably among sites. Lowest values were seen at the inner‐bay site of Saginaw Bay, low to moderate values at the outer‐bay site of Saginaw Bay, and high values at the Lake Erie site. Clearance, pumping and assimilation rates were all highly positively correlated (R² = 0.76) with per cent contribution of flagellates to total algal biomass and negatively correlated with per cent of Microcystis aeruginosa (R² = 0.63). The negative effects on pumping rate (as determined by clearance rate on the <53 μm fraction) of Microcystis, which occurred in the >53 μm fraction, could be mitigated by the presence of flagellates in the <53 μm fraction. 3. Visual observations of mussel feeding showed evidence for poor seston quality during summer negatively affecting feeding rates. High faeces production during times of low assimilation rate was suggestive of poor assimilation efficiency and/or viable gut passage of grazing resistant algae. Long periods of time not filtering by the mussels during some Microcystis blooms and lack of production of a filtering current during one experiment were suggestive of intoxication from microcystin or other secondary compounds. 4. Clearance and feeding rates of the mussels in Saginaw Bay were high during spring and autumn and very low in summer, particularly at the inner‐bay site. Condition of the mussels (mass : length ratio) was highest in spring and lowest during summer. This seasonal variation probably reflected high food assimilation rate during autumn and spring and low assimilation rate and reproduction during summer. The condition of mussels throughout the year was higher at the outer‐bay than the inner‐bay site, reflecting better feeding conditions at the former. Mussel selective feeding may have been responsible for the poor quality of food at the inner bay site; therefore, we postulate that a regime shift in phytoplankton composition promoted by the mussels fed back into lowered condition of the mussels.     

Can Biochar and Phytoextractors Be Jointly Used for Cadmium Remediation?

Phytoremediation of soils contaminated with cadmium was tested after liming (CaO) or biochar addition, using red amaranth (Amaranthus tricolor L.) as test plant species. Two biochars with contrasting characteristics were prepared from two feedstocks and added to the soil at a rate of 3% (w:w): Eucalyptus pyrolysed at 600°C (EB) and poultry litter at 400°C (PLB). Liming was carried out in two treatments (CaO1) and (CaO2) to the same pH as the treatments EB and PLB respectively. Total plant mass increased in soils amended with PLB and with a mixture of PLB and EB; however this was not sufficient to increase the efficiency of phytoextraction. Bioavailable and mobile fractions of Cd diminished after liming or biochar addition. Our study infers that, both the amount of Cd immobilized and the main mechanism responsible for this immobilization varies according to biochar properties.     

Can animals recall the past and plan for the future?

According to the 'mental time travel hypothesis' animals, unlike humans, cannot mentally travel backwards in time to recollect specific past events (episodic memory) or forwards to anticipate future needs (future planning). Until recently, there was little evidence in animals for either ability. Experiments on memory in food-caching birds, however, question this assumption by showing that western scrub-jays form integrated, flexible, trial-unique memories of what they hid, where and when. Moreover, these birds can adjust their caching behaviour in anticipation of future needs. We suggest that some animals have elements of both episodic-like memory and future planning.     

Ascorbic acid oxidase is dynamically regulated by light and oxygen. A tool for oxygen management in plants?

Ascorbic acid oxidase (AAO) is a plant blue-copper protein catalyzing dioxygen reduction to water using ascorbic acid as the electron donor. In spite of extensive molecular characterization the physiological role of AAO is still uncertain. Abundant mRNA, protein and activity of AAO were observed in illuminated leaves of Cucurbita pepo. AAO activity was found to be proportional to light intensity. The light effect was rapidly reversed in dark and activity remained low throughout the dark period. Activity was elicited in dark by increased oxygen concentration. AAO activity increased in the facultative CAM Kalancho? blossfeldiana upon induction of the CAM cycle and decreased during germination of C. pepo and Zea mays under hypoxic conditions. These results strongly suggest that AAO activity could be part of a dynamic system for oxygen management in plants.