Diffusion Boundary Layers Ameliorate the Negative Effects of Ocean Acidification on the Temperate Coralline Macroalga Arthrocardia corymbosa

Anthropogenically-modulated reductions in pH, termed ocean acidification, could pose a major threat to the physiological performance, stocks, and biodiversity of calcifiers and may devalue their ecosystem services. Recent debate has focussed on the need to develop approaches to arrest the potential negative impacts of ocean acidification on ecosystems dominated by calcareous organisms. In this study, we demonstrate the role of a discrete (i.e. diffusion) boundary layer (DBL), formed at the surface of some calcifying species under slow flows, in buffering them from the corrosive effects of low pH seawater. The coralline macroalga Arthrocardia corymbosa was grown in a multifactorial experiment with two mean pH levels (8.05 ‘ambient’ and 7.65 a worst case ‘ocean acidification’ scenario projected for 2100), each with two levels of seawater flow (fast and slow, i.e. DBL thin or thick). Coralline algae grown under slow flows with thick DBLs (i.e., unstirred with regular replenishment of seawater to their surface) maintained net growth and calcification at pH 7.65 whereas those in higher flows with thin DBLs had net dissolution. Growth under ambient seawater pH (8.05) was not significantly different in thin and thick DBL treatments. No other measured diagnostic (recruit sizes and numbers, photosynthetic metrics, %C, %N, %MgCO₃) responded to the effects of reduced seawater pH. Thus, flow conditions that promote the formation of thick DBLs, may enhance the subsistence of calcifiers by creating localised hydrodynamic conditions where metabolic activity ameliorates the negative impacts of ocean acidification.     

Effect of pH on Inorganic Carbon Uptake in Algal Cultures

Biomass production by the green algae Scenedesmus obliquus and Chlorella vulgaris in intensive laboratory continuous cultures was considerably affected by the pH at which the cultures were maintained. Carbon photoassimilation experiments revealed that pH values in the range of 8 to 9 were important for determining the free CO₂ concentrations in the medium. With higher pH values, additional pH effects were observed involving a decrease in the relative high affinity of low CO₂-adapted algae to free CO₂. The carbon uptake rate by high CO₂-adapted algae after transfer to low free CO₂ medium was characterized by a lag period of about 30 min, after which the affinity of the algae to CO₂ increased considerably. Both continuous growth and carbon uptake experiments indicated that artificially maintained high free CO₂ concentrations are recommended for maximal production in intensive outdoor algal cultures.     

Impact of Ocean Warming and Ocean Acidification on Larval Development and Calcification in the Sea Urchin Tripneustes gratilla

Background

As the oceans simultaneously warm, acidify and increase in P _CO2, prospects for marine biota are of concern. Calcifying species may find it difficult to produce their skeleton because ocean acidification decreases calcium carbonate saturation and accompanying hypercapnia suppresses metabolism. However, this may be buffered by enhanced growth and metabolism due to warming.

Methodology/Principal Findings

We examined the interactive effects of near-future ocean warming and increased acidification/P _CO2 on larval development in the tropical sea urchin Tripneustes gratilla. Larvae were reared in multifactorial experiments in flow-through conditions in all combinations of three temperature and three pH/P _CO2 treatments. Experiments were placed in the setting of projected near future conditions for SE Australia, a global change hot spot. Increased acidity/P _CO2 and decreased carbonate mineral saturation significantly reduced larval growth resulting in decreased skeletal length. Increased temperature (+3°C) stimulated growth, producing significantly bigger larvae across all pH/P _CO2 treatments up to a thermal threshold (+6°C). Increased acidity (-0.3-0.5 pH units) and hypercapnia significantly reduced larval calcification. A +3°C warming diminished the negative effects of acidification and hypercapnia on larval growth.

Conclusions and Significance

This study of the effects of ocean warming and CO₂ driven acidification on development and calcification of marine invertebrate larvae reared in experimental conditions from the outset of development (fertilization) shows the positive and negative effects of these stressors. In simultaneous exposure to stressors the dwarfing effects of acidification were dominant. Reduction in size of sea urchin larvae in a high P _CO2 ocean would likely impair their performance with negative consequent effects for benthic adult populations.     

Impacts of Ocean Acidification on Sediment Processes in Shallow Waters of the Arctic Ocean

Despite the important roles of shallow-water sediments in global biogeochemical cycling, the effects of ocean acidification on sedimentary processes have received relatively little attention. As high-latitude cold waters can absorb more CO₂ and usually have a lower buffering capacity than warmer waters, acidification rates in these areas are faster than those in sub-tropical regions. The present study investigates the effects of ocean acidification on sediment composition, processes and sediment-water fluxes in an Arctic coastal system. Undisturbed sediment cores, exempt of large dwelling organisms, were collected, incubated for a period of 14 days, and subject to a gradient of pCO₂ covering the range of values projected for the end of the century. On five occasions during the experimental period, the sediment cores were isolated for flux measurements (oxygen, alkalinity, dissolved inorganic carbon, ammonium, nitrate, nitrite, phosphate and silicate). At the end of the experimental period, denitrification rates were measured and sediment samples were taken at several depth intervals for solid-phase analyses. Most of the parameters and processes (i.e. mineralization, denitrification) investigated showed no relationship with the overlying seawater pH, suggesting that ocean acidification will have limited impacts on the microbial activity and associated sediment-water fluxes on Arctic shelves, in the absence of active bio-irrigating organisms. Only following a pH decrease of 1 pH unit, not foreseen in the coming 300 years, significant enhancements of calcium carbonate dissolution and anammox rates were observed. Longer-term experiments on different sediment types are still required to confirm the limited impact of ocean acidification on shallow Arctic sediment processes as observed in this study.     

The Impact of Ocean Acidification on the Functional Morphology of Foraminifera

Culturing experiments were performed on sediment samples from the Ythan Estuary, N. E. Scotland, to assess the impacts of ocean acidification on test surface ornamentation in the benthic foraminifer Haynesina germanica. Specimens were cultured for 36 weeks at either 380, 750 or 1000 ppm atmospheric CO₂. Analysis of the test surface using SEM imaging reveals sensitivity of functionally important ornamentation associated with feeding to changing seawater CO₂ levels. Specimens incubated at high CO₂ levels displayed evidence of shell dissolution, a significant reduction and deformation of ornamentation. It is clear that these calcifying organisms are likely to be vulnerable to ocean acidification. A reduction in functionally important ornamentation could lead to a reduction in feeding efficiency with consequent impacts on this organism''s survival and fitness.     

Effect of Vanadate on Microsomal ATPase Activity, Acidification of the Medium and Auxin-stimulated Growth in Pea and Cucumber

The relationship between ATPase activity, medium acidificationand auxin-stimulated growth in segments of pea stem (Pisum sativumL., cv. Alaska) and cucumber hypocotyl (Cucumis sativus L.,cv. Long Green Ridge) was investigated using sodium orthovanadate,widely used as a selective inhibitor of plasma membrane-associatedATPase activity. ATPase activity of cucumber microsomal preparationswas about seven times lower than similar preparations from pea(on a mg microsomal protein basis) and was much more effectivelyinhibited by vanadate. Similarly, acidification of the mediumby abraded cucumber segments occurred to a lesser extent thanwith pea and showed a greater inhibition by vanadate. Both growthin controls and auxin-stimulated growth of cucumber segmentswere strongly inhibited by vanadate, whereas in pea auxin-stimulatedgrowth was reduced by only half and controls showed little inhibition.Acidification of the medium by segments of both species wasfound to occur readily even in controls and showed little promotionin the presence of IAA, although growth in both species wasrapidly and significantly promoted by IAA. These results indicatethat acidification is brought about by a plasma membrane-associatedATPase, and suggest that while acidification is an essentialfactor for auxin-stimulated growth it may not be the mechanismby which the growth rate is controlled. ATPase, Cucumis sativus, indole-3-acetic acid, Pisum sativum, vanadate     

凋落物对土壤酸化的缓冲及其对根系生长的影响

凋落物层是森林生态系统中一个十分活跃的界面,一方面环境因素影响凋落物的积累和分解,另一方面凋落物的动态反过来又影响到系统内的水热收支平衡、土壤的理化特性以至森林生产力。值得注意的是,在高度工业化的现代社会,大气污染作为一种新生的环境因子不同程度地作用于森林生态系统,凋落物层则是大气污染物(如酸雨)作用于森林土壤亚系     

Effects of Acetaldehyde on Growth and Biosynthesis in an Algal Flagellate Polytomella caeca*

SYNOPSIS. Eight mM acetaldehyde prevented growth of Polytomella caeca in acetate medium and differentially changed the labeling by acetate-2-¹⁴C of chromatographically separated RNA hydrolysate products. Four mM acetaldehyde also prevented growth in acetate medium unless uridine, thymidine, guanosine, uracil, thymine or quanine were present; then growth was delayed by 2 or 4 days. Orotidine, orotic acid, dihydroortic acid, cytosine, cytidine, adenosine and adenine had no effect on growth in acetate medium containing 4 mM acetaldehyde. One mM acetaldehyde promoted growth in acetate medium and also could serve as a sole carbon source. One mM propionaldehyde, but not butyraldehyde, was also an adequate carbon source. Four mM acetaldehyde, as a sole carbon source, supported growth only when uridine was present.     

Composition,Buoyancy Regulation and Fate of Ice Algal Aggregates in the Central Arctic Ocean

Sea-ice diatoms are known to accumulate in large aggregates in and under sea ice and in melt ponds. There is recent evidence from the Arctic that such aggregates can contribute substantially to particle export when sinking from the ice. The role and regulation of microbial aggregation in the highly seasonal, nutrient- and light-limited Arctic sea-ice ecosystem is not well understood. To elucidate the mechanisms controlling the formation and export of algal aggregates from sea ice, we investigated samples taken in late summer 2011 and 2012, during two cruises to the Eurasian Basin of the Central Arctic Ocean. Spherical aggregates densely packed with pennate diatoms, as well as filamentous aggregates formed by Melosira arctica showed sign of different stages of degradation and physiological stoichiometries, with carbon to chlorophyll a ratios ranging from 110 to 66700, and carbon to nitrogen molar ratios of 8–35 and 9–40, respectively. Sub-ice algal aggregate densities ranged between 1 and 17 aggregates m⁻², maintaining an estimated net primary production of 0.4–40 mg C m⁻² d⁻¹, and accounted for 3–80% of total phototrophic biomass and up to 94% of local net primary production. A potential factor controlling the buoyancy of the aggregates was light intensity, regulating photosynthetic oxygen production and the amount of gas bubbles trapped within the mucous matrix, even at low ambient nutrient concentrations. Our data-set was used to evaluate the distribution and importance of Arctic algal aggregates as carbon source for pelagic and benthic communities.     

Effect of Associated Bacteria on the Growth and Toxicity of Alexandrium catenella

Saprophytic bacteria in cultures of the marine dinoflagellate Alexandrium catenella were removed to assess their effect on growth and paralytic shellfish poisoning toxin production of this dinoflagellate. The actual axenic status was demonstrated by the lack of observable bacteria both immediately after treatment and following extended incubation in the absence of antibiotics. Bacteria were measured by counting CFU and also by epifluorescence microscopy and PCR amplification of bacterial 16S-23S spacer ribosomal DNA to detect noncultivable bacteria. Removal of bacteria did not have any effect on the growth of the dinoflagellate except for the inhibition of A. catenella disintegration after reaching the stationary phase. Toxicity was determined in dinoflagellate cell extracts by different methods: high-performance liquid chromatography (HPLC); an electrophysiological test called the Electrotest, which measures the inhibition of saxitoxin-sensitive Na⁺ channels expressed in a cell line; and a mouse bioassay, which measures the toxic effect on the whole mammal neuromuscular system. A lower toxicity of the dinoflagellates in axenic culture was observed by these three methods, though the difference was significant only by the mouse bioassay and HPLC methods. Altogether the results indicate that axenic cultures of A. catenella are able to produce toxin, though the total toxicity is probably diminished to about one-fifth of that in nonaxenic cultures.     

Effects of Ocean Acidification on Juvenile Red King Crab (Paralithodes camtschaticus) and Tanner Crab (Chionoecetes bairdi) Growth,Condition, Calcification,and Survival

Ocean acidification, a decrease in the pH in marine waters associated with rising atmospheric CO₂ levels, is a serious threat to marine ecosystems. In this paper, we determine the effects of long-term exposure to near-future levels of ocean acidification on the growth, condition, calcification, and survival of juvenile red king crabs, Paralithodes camtschaticus, and Tanner crabs, Chionoecetes bairdi. Juveniles were reared in individual containers for nearly 200 days in flowing control (pH 8.0), pH 7.8, and pH 7.5 seawater at ambient temperatures (range 4.4–11.9 °C). In both species, survival decreased with pH, with 100% mortality of red king crabs occurring after 95 days in pH 7.5 water. Though the morphology of neither species was affected by acidification, both species grew slower in acidified water. At the end of the experiment, calcium concentration was measured in each crab and the dry mass and condition index of each crab were determined. Ocean acidification did not affect the calcium content of red king crab but did decrease the condition index, while it had the opposite effect on Tanner crabs, decreasing calcium content but leaving the condition index unchanged. This suggests that red king crab may be able to maintain calcification rates, but at a high energetic cost. The decrease in survival and growth of each species is likely to have a serious negative effect on their populations in the absence of evolutionary adaptation or acclimatization over the coming decades.     

Effect of pH on Bacillus thermoamylovorans Growth and Glucose Fermentation

The effect of pH on the growth and physiology of Bacillus thermoamylovorans, a new moderately thermophilic and non-spore-forming bacterium isolated from palm wine, was studied. Growth occurred from pH 5.4 to 8.5, with optimum growth at 7.0. During the exponential growth phase at optimum pH, glucose was consumed at the maximum rate (qs), 17.87 mmol g(sup-1) h(sup-1), and was mainly fermented into acetate, ethanol, and formate (76.5% of metabolites produced). In acidic or alkaline conditions, glucose specific consumption rates were considerably reduced (qs = 8.06 mmol g(sup-1) h(sup-1) at pH 5.6 and 2.85 mmol g(sup-1) h(sup-1) at pH 8.4), and a switch in glucose metabolism toward lactate production (62.6% of metabolites produced at pH 5.6 and 41.2% of those produced at pH 8.4) was observed. Moreover, optimum cellular yield (Y(infx/ATP)), 14.8 g mol(sup-1), and optimum energy yield (Y(infATP/s)), 2.65 mol mol(sup-1), were observed at neutrality. The results of this study were compared with published data about lactic acid bacteria; this comparison allowed us to complement our previous taxonomic study of B. thermoamylovorans and to identify additional phenotypic differences between B. thermoamylovorans and lactobacilli.     

Small‐Sized Benthic Organisms of the Alpha Ridge,Central Arctic Ocean

Abundance, biomass and activity of the small‐sized benthic organisms (bacteria to meiofauna, including foraminifera) was studied in summer 1998 during the expedition ARK XIV/1a to the Amerasian area of the perennially ice covered central Arctic Ocean. With the help of two icebreakers, the German research vessel POLARSTERN and the Russian nuclear‐powered ARCTICA, it was possible to reach this remote, heavily ice‐covered region in order to carry out the first benthic investigations. These focus on effects on the benthic community of the expected low food availability under perennial ice coverage. Bacterial and meiofaunal abundances were determined by direct counting. Biomass determinations on bacteria and nematodes were undertaken by size‐imaging techniques. In addition biochemical analyses were carried out to estimate food availability (as sediment‐bound chloroplastic pigments indicating phytodetritus) at the sea floor, the total microbial biomass (TMB; i.e. the total amount of sediment inhabiting bacteria, flagellata, protozoa and small metazoa, estimated by phospholipid quantification) and the potential bacterial activity (turnover rates of ester‐cleaving exoenzymes). Concentrations of chloroplastic pigment equivalents (CPE) in the main target area (Alpa‐Ridge) ranged between 0.10 ± 0.02 and 0.17 ± 0.04 μg/ml. A 2–3 times higher concentration was determined at a station on the Lomonosov Ridge crest (0.40 ± 0.15 μg/ml). The standing stock of meiobenthic organisms (including foraminiferans) was extremely low and varied between 72 ± 17 individuals 10 cm^–2 in the deep Makarov Basin (3,170 m) and 190 ± 56 individuals 10 cm^–2 on the Alpha Ridge (1,470 m). Significantly higher numbers (U‐test, p = 0.049) were found on the Lomonosov Ridge (297 ± 82 individuals 10 cm^–2). Meiobenthic abundances from the area of investigations, were up to ten times lower than those reported from non‐ice covered deep‐sea regions. However a significant water depth depending decrease of meiobenthic abundances was still detectable. A comparison of biomass data determined by volumetric measurements and biochemical methods showed that about 67% of the TMB are held by organisms of nanofauna size (2–32 μm), approx. 32% belongs to bacteria. Only 0.5–1.5% of the TMB were held by metazoan meiofauna.     

Acidification of the Medium Associated with Normal and Fusicoccin-Induced Seed Germination

Fusicoccin, a toxin stimulating cell enlargement and inducing proton extrusion in various plant tissues, has been shown to replace kinetin, gibberellic acid and red light in breaking seed dormancy. It also removes the inhibitory effect of abscisic acid. The present data also show that the stimulating effect of fucicoccin on embryo growth of decoated radish (Raphanus sativus L.) and maize (Zea mays) seeds and on the development of maize embryos is accompanied by an early, significant acidification of the medium. Acidification of the medium is also observed when fusicoccin reverses the abscisic acid-induced inhibition of germination. These results support the hypothesis that the mode of action of fusicoccin in promoting germination involves, as in stimulation of cell enlargement, the activation at the cell membrane level of proton extrusion processes. The physiological significance of fusicoccin-induced release of protons at the onset of germination is discussed in comparison with the results concerning the mechanism of action of fusicoccin on cell enlargement in other plant materials.     

Bacteria Associated with Benthic Diatoms from Lake Constance: Phylogeny and Influences on Diatom Growth and Secretion of Extracellular Polymeric Substances

The composition of diatom-associated bacterial communities was studied with 14 different unialgal xenic diatom cultures isolated from freshwater epilithic biofilms of Lake Constance, Germany. A clear dominance of Alphaproteobacteria was observed, followed by Betaproteobacteria, Gammaproteobacteria, Bacteroidetes, and Verrucomicrobia. Pure cultures of the diatom Cymbella microcephala, which was found to be dominant in epilithic biofilms in Lake Constance, were cocultivated with six associated bacterial strains. All these bacterial strains were able to grow in C. microcephala cultures in the absence of organic cosubstrates. Diatom growth was generally enhanced in the presence of bacteria, and polysaccharide secretion was generally increased in the presence of Proteobacteria. The monomer composition of extracellular polysaccharides of C. microcephala changed in relation to the presence of different bacteria, but the dominant monomers were less affected. Our results indicate that these changes were caused by the diatom itself rather than by specific bacterial degradation. One Bacteroidetes strain strongly influenced carbohydrate secretion by the alga via extracellular soluble compounds. Biofilms were formed only in the presence of bacteria. Phylogenetic analysis and coculture studies indicate an adaptation of Proteobacteria and Bacteroidetes to the microenvironment created by the diatom biofilm.     

Effects of Ocean Acidification on the Ballast of Surface Aggregates Sinking through the Twilight Zone

The dissolution of CaCO₃ is one of the ways ocean acidification can, potentially, greatly affect the ballast of aggregates. A diminution of the ballast could reduce the settling speed of aggregates, resulting in a change in the carbon flux to the deep sea. This would mean lower amounts of more refractory organic matter reaching the ocean floor. This work aimed to determine the effect of ocean acidification on the ballast of sinking surface aggregates. Our hypothesis was that the decrease of pH will increase the dissolution of particulate inorganic carbon ballasting the aggregates, consequently reducing their settling velocity and increasing their residence time in the upper twilight zone. Using a new methodology for simulation of aggregate settling, our results suggest that future pCO₂ conditions can significantly change the ballast composition of sinking aggregates. The change in aggregate composition had an effect on the size distribution of the aggregates, with a shift to smaller aggregates. A change also occurred in the settling velocity of the particles, which would lead to a higher residence time in the water column, where they could be continuously degraded. In the environment, such an effect would result in a reduction of the carbon flux to the deep-sea. This reduction would impact those benthic communities, which rely on the vertical flow of carbon as primary source of energy.     

Evolution of the Northern Rockweed,Fucus distichus,in a Regime of Glacial Cycling: Implications for Benthic Algal Phylogenetics

Northern hemisphere rockweeds (Fucus) are thought to have evolved in the North Pacific and then spread to the North Atlantic following the opening of the Bering Strait. They have dispersed and widely speciated in the North Atlantic and its tributary seas. Fucus distichus is likely near the ancestral member of this genus, and studies have shown that there are several species/subspecies in this complex (i.e. F. evanescens and F. gardneri). We used phylogenetic and haplotype analyses to test the phylogenetic relationships and biogeography of F. distichus. Our data and subsequent analyses demonstrate that, unlike previous studies that lacked samples from an extensive geographical area of the Arctic and Subarctic, there is a distinct Arctic haplotype that is the source of subspecies in both the North Pacific and North Atlantic. Fucus distichus occupies a low tide zone habitat, and in Arctic/Subarctic regions it is adapted to the severe stress of sea ice coverage and disturbance during many months per year. We hypothesize that the very large geographic area of Arctic and Subarctic rocky shores available to this species during interglacials, supported by large Arctic/Subarctic fringe areas as well as unglaciated refugia during glacial cycles, provided a robust population and gene pool (described by the Thermogeographic Model). This gene pool dilutes that of the more fragmented and area-limited Temperate/Boreal area populations when they are brought together during glacial cycles. We suggest that similar subspecies complexes for a variety of Arctic/Subarctic shore biota should be examined further in this context, rather than arbitrarily being split up into numerous species.     

pH Dependence of the Copper Effect on Flowering, Growth and Chlorophyll Content in Lemna paucicostata 6746

The short-day plant Lemna paucicostata 6746 took up the sameamount of copper from the medium whether the pH of the mediumwas 4.1 or 5.1. At pH 4.1, an addition of copper to the mediumresulted in an unchanged chlorophyll content, a somewhat reducedgrowth rate and a substantial induction of long-day flowering.By contrast, at pH 5.1 the same copper concentration causeda reduction in the chlorophyll content and strong inhibitionof growth, but it did not induce any long-day flowering. (Received June 14, 1982; Accepted October 14, 1982)     

Impact of Ocean Acidification on Ecosystem Functioning and Services in Habitat-Forming Species and Marine Ecosystems

Ecosystems - Ocean acidification (OA) is expected to impact habitat-forming species (HFS), with cascading effects on the whole marine ecosystem and related services that are seldom quantified....