Effects of adaptation, chance, and history on the evolution of the toxic dinoflagellate Alexandrium minutum under selection of increased temperature and acidification

The roles of adaptation, chance, and history on evolution of the toxic dinoflagellate Alexandrium minutum Halim, under selective conditions simulating global change, have been addressed. Two toxic strains (AL1V and AL2V), previously acclimated for two years at pH 8.0 and 20°C, were transferred to selective conditions: pH 7.5 to simulate acidification and 25°C. Cultures under selective conditions were propagated until growth rate and toxin cell quota achieved an invariant mean value at 720 days (ca. 250 and ca. 180 generations for strains AL1V and AL2V, respectively). Historical contingencies strongly constrained the evolution of growth rate and toxin cell quota, but the forces involved in the evolution were not the same for both traits. Growth rate was 1.5-1.6 times higher than the one measured in ancestral conditions. Genetic adaptation explained two-thirds of total adaptation while one-third was a consequence of physiological adaptation. On the other hand, the evolution of toxin cell quota showed a pattern attributable to neutral mutations because the final variances were significantly higher than those measured at the start of the experiment. It has been hypothesized that harmful algal blooms will increase under the future scenario of global change. Although this study might be considered an oversimplification of the reality, it can be hypothesized that toxic blooms will increase but no predictions can be advanced about toxicity.     

Microenvironmental changes support evidence of photosynthesis and calcification inhibition in Halimeda under ocean acidification and warming

The effects of elevated CO₂ and temperature on photosynthesis and calcification of two important calcifying reef algae (Halimeda macroloba and Halimeda cylindracea) were investigated with O₂ microsensors and chlorophyll a fluorometry through a combination of two pCO₂ (400 and 1,200 μatm) and two temperature treatments (28 and 32 °C) equivalent to the present and predicted conditions during the 2100 austral summer. Combined exposure to pCO₂ and elevated temperature impaired calcification and photosynthesis in the two Halimeda species due to changes in the microenvironment around the algal segments and a reduction in physiological performance. There were no significant changes in controls over the 5-week experiment, but there was a 50–70 % decrease in photochemical efficiency (maximum quantum yield), a 70–80 % decrease in O₂ production and a threefold reduction in calcification rate in the elevated CO₂ and high temperature treatment. Calcification in these species is closely coupled with photosynthesis, such that a decrease in photosynthetic efficiency leads to a decrease in calcification. Although pH seems to be the main factor affecting Halimeda species, heat stress also has an impact on their photosystem II photochemical efficiency. There was a strong combined effect of elevated CO₂ and temperature in both species, where exposure to elevated CO₂ or temperature alone decreased photosynthesis and calcification, but exposure to both elevated CO₂ and temperature caused a greater decline in photosynthesis and calcification than in each stress individually. Our study shows that ocean acidification and ocean warming are drivers of calcification and photosynthesis inhibition in Halimeda. Predicted climate change scenarios for 2100 would therefore severely affect the fitness of Halimeda, which can result in a strongly reduced production of carbonate sediments on coral reefs under such changed climate conditions.     

Effects of seawater acidification on a coral reef meiofauna community

Despite the increasing risk that ocean acidification will modify benthic communities, great uncertainty remains about how this impact will affect the lower trophic levels, such as members of the meiofauna. A mesocosm experiment was conducted to investigate the effects of water acidification on a phytal meiofauna community from a coral reef. Community samples collected from the coral reef subtidal zone (Recife de Fora Municipal Marine Park, Porto Seguro, Bahia, Brazil), using artificial substrate units, were exposed to a control pH (ambient seawater) and to three levels of seawater acidification (pH reductions of 0.3, 0.6, and 0.9 units below ambient) and collected after 15 and 30 d. After 30 d of exposure, major changes in the structure of the meiofauna community were observed in response to reduced pH. The major meiofauna groups showed divergent responses to acidification. Harpacticoida and Polychaeta densities did not show significant differences due to pH. Nematoda, Ostracoda, Turbellaria, and Tardigrada exhibited their highest densities in low-pH treatments (especially at the pH reduction of 0.6 units, pH 7.5), while harpacticoid nauplii were strongly negatively affected by low pH. This community-based mesocosm study supports previous suggestions that ocean acidification induces important changes in the structure of marine benthic communities. Considering the importance of meiofauna in the food web of coral reef ecosystems, the results presented here demonstrate that the trophic functioning of coral reefs is seriously threatened by ocean acidification.     

Effects of seawater acidification on cell cycle control mechanisms in Strongylocentrotus purpuratus embryos

Previous studies have shown fertilization and development of marine species can be significantly inhibited when the pH of sea water is artificially lowered. Little mechanistic understanding of these effects exists to date, but previous work has linked developmental inhibition to reduced cleavage rates in embryos. To explore this further, we tested whether common cell cycle checkpoints were involved using three cellular biomarkers of cell cycle progression: (1) the onset of DNA synthesis, (2) production of a mitotic regulator, cyclin B, and (3) formation of the mitotic spindle. We grew embryos of the purple sea urchin, Strongylocentrotus purpuratus, in seawater artifically buffered to a pH of ～7.0, 7.5, and 8.0 by CO(2) infusion. Our results suggest the reduced rates of mitotic cleavage are likely unrelated to common cell cycle checkpoints. We found no significant differences in the three biomarkers assessed between pH treatments, indicating the embryos progress through the G(1)/S, G(2)/M and metaphase/anaphase transitions at relatively similar rates. These data suggest low pH environments may not impact developmental programs directly, but may act through secondary mechanisms such as cellular energetics.     

海水酸化及升温对刺参稚参生长和变色的影响

海洋酸化和海洋变暖是当下及未来海洋生物及其依存生态系统面临的主要环境压力和生态问题。当前,海洋生物早期发育气候变化生物学的研究主要集中于海洋酸化的影响,为了更好地探究海洋气候变化对海洋生物的影响,有必要研究海洋酸化和变暖联合作用下海洋生物的生态响应。以受精后24天的刺参稚参为研究对象,通过模拟当前和本世纪末海洋环境,观察海水酸化和升温对刺参稚参在体色发育关键时期生长、发育及体色变化的影响。实验设置对照组(大连近海水温,pCO₂ 400 mg·kg^-1)、升温组(对照组水温+2℃,pCO₂ 400 mg·kg^-1)、酸化组(对照组水温,pCO₂ 1000 mg·kg^-1)、酸化升温组(对照组水温+2℃,pCO₂ 1000 mg·kg^-1)。结果表明:温度升高2℃能够显著提高稚参发育速率,体色变化加快; pH值降低0.23个单位显著延迟稚参生长,体色变化减缓,个体间体重差异变大;升温2℃能抵消pH降低0.23个单位对...     

Ocean acidification alters temperature and salinity preferences in larval fish

Ocean acidification alters the way in which animals perceive and respond to their world by affecting a variety of senses such as audition, olfaction, vision and pH sensing. Marine species rely on other senses as well, but we know little of how these might be affected by ocean acidification. We tested whether ocean acidification can alter the preference for physicochemical cues used for dispersal between ocean and estuarine environments. We experimentally assessed the behavioural response of a larval fish (Lates calcarifer) to elevated temperature and reduced salinity, including estuarine water of multiple cues for detecting settlement habitat. Larval fish raised under elevated CO₂ concentrations were attracted by warmer water, but temperature had no effect on fish raised in contemporary CO₂ concentrations. In contrast, contemporary larvae were deterred by lower salinity water, where CO₂-treated fish showed no such response. Natural estuarine water—of higher temperature, lower salinity, and containing estuarine olfactory cues—was only preferred by fish treated under forecasted high CO₂ conditions. We show for the first time that attraction by larval fish towards physicochemical cues can be altered by ocean acidification. Such alterations to perception and evaluation of environmental cues during the critical process of dispersal can potentially have implications for ensuing recruitment and population replenishment. Our study not only shows that freshwater species that spend part of their life cycle in the ocean might also be affected by ocean acidification, but that behavioural responses towards key physicochemical cues can also be negated through elevated CO₂ from human emissions.     

Shell mineralogical trends in epifaunal Mesozoic bivalves and their relationship to seawater chemistry and atmospheric carbon dioxide concentration

The Late Triassic-Early Jurassic change from aragonite- to calcite-facilitating conditions in the oceans, which was caused by a decrease of the Mg²⁺/Ca²⁺ ratio of seawater in combination with an increase of the partial pressure of carbon dioxide, also affected the shell mineralogy of epifaunal bivalves. In the “calcite sea” of the Jurassic and Cretaceous, the most diverse and abundant families of epifaunal bivalves had largely calcitic shells. Some of them, such as the Inoceramidae, acquired this shell mineralogy earlier in Earth's history but did not significantly diversify until the onset of “calcite sea” conditions. Others, however, replaced aragonite by calcite in their shell at the beginning of the Jurassic, as shown for the Ostreidae, Gryphaeidae, Pectinidae, Plicatulidae, and Buchiidae. In these families, replacement of aragonite by calcite took place in the middle and inner layer of the shell and was not associated with changes in morphology and life habit. It is therefore proposed that lower metabolic costs rather than higher resistance against dissolution or advantageous physical properties triggered the calcite expansion in their shells. This explanation fits well the observation that clades of thin-shelled bivalves were less affected by the change of seawater chemistry. Thick-shelled clades, by contrast, may suffer a severe decline in diversity until they adapt their shell mineralogy, as demonstrated by the Hippuritoida: The diversity of the Megalodontoidea, which failed to adapt their shell mineralogy to “calcite sea” conditions, dramatically decreased at the end of the Triassic, whereas their descendents became dominant carbonate producers during the Late Mesozoic after they acquired a calcitic outer shell layer in the Late Jurassic. These examples indicate that changes in the seawater chemistry and in the partial pressure of carbon dioxide are factors that influence the diversity of carbonate-secreting animals, and, as in the case of the decline of the Megalodontoidea, may contribute to mass extinctions.     

Response of larval barnacle proteome to CO(2)-driven seawater acidification

The majority of benthic marine invertebrates have a complex life cycle, during which the pelagic larvae select a suitable substrate, attach to it, and then metamorphose into benthic adults. Anthropogenic ocean acidification (OA) is postulated to affect larval metamorphic success through an altered protein expression pattern (proteome structure) and post-translational modifications. To test this hypothesis, larvae of an economically and ecologically important barnacle species Balanus amphitrite, were cultured from nauplius to the cyprid stage in the present (control) and in the projected elevated concentrations of CO₂ for the year 2100 (the OA treatment). Cyprid response to OA was analyzed at the total proteome level as well as two protein post-translational modification (phosphorylation and glycosylation) levels using a 2-DE based proteomic approach. The cyprid proteome showed OA-driven changes. Proteins that were differentially up or down regulated by OA come from three major groups, namely those related to energy-metabolism, respiration, and molecular chaperones, illustrating a potential strategy that the barnacle larvae may employ to tolerate OA stress. The differentially expressed proteins were tentatively identified as OA-responsive, effectively creating unique protein expression signatures for OA scenario of 2100. This study showed the promise of using a sentinel and non-model species to examine the impact of OA at the proteome level.     

First respiration estimates of cold-seep vesicomyid bivalves from in situ total oxygen uptake measurements

Vesicomyid bivalves are one of the most abundant symbiont-bearing species inhabiting deep-sea reducing ecosystems. Nevertheless, except for the hydrothermal vent clam Calyptogena magnifica, their metabolic rates have not been documented, and only assessed with ex situ experiments. In this study, gathering benthic chamber measurements and biomass estimation, we give the first in situ assessment of the respiration rate of these bivalves. The giant pockmark Regab, located at 3160m depth along the Congo-Angola margin, is a cold-seep site characterised by dense assemblages of two species of vesicomyids: Christineconcha regab and Laubiericoncha chuni with high dominance of C. regab. Two sites with dense aggregates of vesicomyids were selected to measure total oxygen uptake (TOU), and methane fluxes using IFREMER's benthic chamber CALMAR deployed by the ROV Quest 4000 (MARUM). Photographs were taken and bivalves were sampled using blade corers to estimate density and biomass. Total oxygen uptake was higher at Site 2 compared to Site 1 (respectively 492 mmol.m(-2).d(-1) and 332 mmol.m(-2).d(-1)). However, given vesicomyid densities and biomass, mean oxygen consumption rates were similar at both sites (1.9 to 2.5 μmol.g total dry mass(-1).h(-1) at the Site 1 and 1.8 to 2.3 μmol.g total dry mass(-1).h(-1) at Site 2). These respiration rates are higher than published ex situ estimates for cold-seep or hydrothermal vent bivalves. Although methane fluxes at the base of sulphide production were clearly higher at Site 2 (14.6 mmol.m(-2).d(-1)) than at Site 1 (0.3 mmol.m(-2).d(-1)), they do not seem to influence the respiration rates of these bivalves associated to sulphide-oxidizing symbionts.     

Ocean temperature,but not acidification,causes sea anemone bleaching under a near-future climate scenario

Coral Reefs - Climate change is causing ocean temperature and partial pressure of carbon dioxide (pCO2) to increase. For sea anemones that have Symbiodiniaceae, high temperatures induce bleaching,...     

Effects of seawater acidification and salinity alterations on metabolic,osmoregulation and oxidative stress markers in Mytilus galloprovincialis

The impacts of seawater acidification and salinity shifts on metabolism, energy reserves, and oxidative status of mussels have been largely neglected. With the aim to increase the current knowledge for the mussel Mytilus galloprovincialis a 28-day chronic test was conducted during which mussels were exposed to two pH (7.8 and 7.3; both at control salinity 28) and three salinity (14, 28 and 35, at control pH, 7.8) levels. After exposure to different conditions, mussels electron transport system activity, energy reserves (protein and glycogen content) carbonic anhydrase activity, antioxidant defences and cellular damage were measured. Results obtained showed that mussels exposed to seawater acidification presented decreased metabolic capacity that may have induced lower energy expenditure (observed in higher glycogen, protein and lipids content at this condition). Low pH condition induced the increase of carbonic anhydrase activity that was related to acid-base balance, while no significant activation of antioxidant defence mechanisms was observed resulting in higher LPO. Regarding the impacts of salinity, the present study showed that at the highest salinity (35) mussels presented lower metabolic activity (also related to lower energetic expenditure) and an opposite response was observed at salinity 14. Carbonic anhydrase slightly increased at stressful salinity conditions, a mechanism of homeostasis maintenance. Lower metabolic activity at the highest salinity, probably related to valves closure, helped to mitigate the increase of LPO in this condition. At low salinity (14), despite an increase of antioxidant enzymes activity, LPO increased, probably as a result of ROS overproduction from higher electron transport system activity. The present findings demonstrated that Mytilus galloprovincialis oxidative status and metabolic capacity were negatively affected by low pH and salinity changes, with alterations that may lead to physiological impairments namely on mussels reproductive output, growth performance and resistance to disease, with ecological and economic implications.Indicators: Physiological and biochemical changes in Mytilus galloprovincialis in response to low pH and salinity changes     

Combined ocean acidification and low temperature stressors cause coral mortality

Oceans are predicted to become more acidic and experience more temperature variability—both hot and cold—as climate changes. Ocean acidification negatively impacts reef-building corals, especially when interacting with other stressors such as elevated temperature. However, the effects of combined acidification and low temperature stress have yet to be assessed. Here, we exposed nubbins of the scleractinian coral Montipora digitata to ecologically relevant acidic, cold, or combined stress for 2 weeks. Coral nubbins exhibited 100% survival in isolated acidic and cold treatments, but ~30% mortality under combined conditions. These results provide further evidence that coupled stressors have an interactive effect on coral physiology, and reveal that corals in colder environments are also susceptible to the deleterious impacts of coupled ocean acidification and thermal stress.     

Response of Mediterranean coralline algae to ocean acidification and elevated temperature

The effects of elevated partial pressure of CO₂ ( p CO₂) and temperature, alone and in combination, on survival, calcification and dissolution were investigated in the crustose coralline alga Lithophyllum cabiochae . Algae were maintained in aquaria during 1 year at near-ambient conditions of irradiance, at ambient or elevated temperature (+3 °C) and at ambient [ca. 400 parts per million (ppm)] or elevated p CO₂ (ca. 700 ppm). Algal necroses appeared at the end of summer under elevated temperature first at 700 ppm (60% of the thallus surface) and then at 400 ppm (30%). The death of algae was observed only under elevated temperature and was two- to threefold higher under elevated p CO₂. During the first month of the experiment, net calcification was significantly reduced under elevated p CO₂. At the end of the summer period, net calcification decreased by 50% when both temperature and p CO₂ were elevated while no effect was found under elevated temperature and elevated p CO₂ alone. In autumn and winter, net calcification in healthy algae increased with increasing temperature, independently of the p CO₂ level, while necroses and death in the algal population caused a net dissolution at elevated temperature and p CO₂. The dissolution of dead algal thalli was affected by elevated p CO₂, being two- to fourfold higher than under ambient p CO₂. These results suggest that net dissolution is likely to exceed net calcification in L. cabiochae by the end of this century. This could have major consequences in terms of biodiversity and biogeochemistry in coralligenous communities dominated by these algae.     

Tumor oxygenation and acidification are increased in melanoma xenografts after exposure to hyperglycemia and meta-iodo-benzylguanidine

Tumor oxygen tension and extracellular pH (pH(e)) are physiological parameters that can be manipulated to improve current cancer therapies. Many human tumors consist of cells that are chronically exposed to low pH(e). Exposure of tumor cells in culture to glucose decreases oxygen consumption (oxygen sparing or Crabtree effect), and while this effect is absent in low pH-adapted tumor cells, it can be restored by combining the respiratory inhibitor meta-iodo-benzylguanidine (MIBG) with glucose (Burd et al., Cancer Res. 61, 5630-5635, 2001). The effects of hyperglycemia and MIBG on tumor oxygen tension and on pH(e) were investigated in human melanoma xenografts in SCID mice. An oral gavage of 1 M glucose (2 g/kg) increased the average blood glucose concentration from <140 mg/dl to approximately 400 mg/dl. Although tumor pH(e) decreased from pH 6.7 to pH 6.5 (P < 0.01) after about 60 min, no change in tumor oxygen tension was observed. However, when oral glucose and MIBG (15 mg/kg) were administered together, oxygen tension increased from 2.8 mmHg to approximately 17 mmHg, and tumor pH(e) decreased from pH 6.7 to pH 6.3 (P < 0.01) after about 115 min. In conclusion, administration of glucose together with MIBG increases tumor oxygen tension and also increases the magnitude and duration of acidification. Hyperglycemia plus MIBG has the potential to improve response to radiation therapy as well as to hyperthermia and some chemotherapies.     

Comparative analyses of viable bacterial counts in foods and seawater under microplate based liquid- and conventional agar plate cultivation: increased culturability of marine bacteria under liquid cultivation

Bacterial counts under liquid cultivation using 96-well microplates were performed. The counts under liquid and under solid cultivation were equivalent in foods, although the counts under liquid cultivation exceeded those under solid cultivation in seawater, suggesting that some bacteria in seawater were viable but did not form detectable colonies. Phylogenetic analysis of bacteria obtained under liquid cultivation was also performed.     

First evidence of enterobiasis in ancient Egypt

The oldest and most common parasite for which we have direct evidence, in the New World, is Enterobius vernicularis. Numerous archaeological sites, especially in the arid American southwest, have yielded fecal samples positive for pinworm ova, some of these dating back 10,000 yr. Reports of pinworm from the Old World are scarce. This article reports the first evidence of pinworm infection from Roman-occupied (30 BC-AD 395) Egypt.     

Rate of soil acidification under wheat in a semi-arid environment

The rate of acidification under wheat in south-eastern Australia was examined by measuring the fluxes of protons entering and leaving the soil, using the theoretical framework of Helyar and Porter (1989). Monthly proton budgets were estimated for the root zone (0–90 cm layer) and for the 0–25 and 25–90 cm layers. After an annual cycle, the root zone was alkalinized by 0.5 to 3.1 kmol OH^- ha^-1. The alkalinity originated from the mineralization of the organic anions contained in the organic matter. The budget was near neutrality in the 0–25 cm layer (range: –1.0 to 1.4 kmol H⁺ ha^-1), whereas there was net alkalinization in the 25–90 cm layer (1.7 to 2.3 kmol OH^- ha^-1). In the 0–25 cm layer, the acidity produced in autumn by mineralization of organic nitrogen was counterbalanced by the alkalinity released from crop residues. The main acidifying factor in this layer was leaching of NO₃ ^- during early winter (2.4 kmol H⁺ ha^-1). Nitrate added through leaching was the main alkalinizing factor in the 25–90 cm layer, as added NO₃ ^- was taken up by the roots or denitrified in this layer. Urea fertilization had almost no effect on the rate of acidification, as little NO₃ ^- was leached out of the root zone. The factors acidifying the soil under wheat were limited in this environment because of the small amout of NO₃ ^- leached and the retention of the crop residues.     

Oxygen solubility in evaporated seawater as a function of temperature and salinity

Most studies of oxygen solubility values for high salinity conditions have used synthetic solutions. The object of this study is therefore to propose an equation, valid for high salinity conditions, based on the analysis of oxygen saturation in evaporated seawater. In this study, the solubility of oxygen in evaporated seawater has been determined over a temperature range of 8–35°C and with salinity values of up to 133‰. Based on experimental data, an equation is proposed that introduces a S ² (salinity) term, at 1 atm pressure, giving increased importance to salinity. The equation provides a valid means of predicting the amount of dissolved oxygen in this range of temperatures and salinities. In addition, for high salinity conditions, with this equation there is no need to extrapolate other established equations, which are less accurate at salinities higher than 40‰. The use of the proposed equation offers a more precise way of calculating oxygen solubility in seawater at high salinity values (up to 133‰), and small deviations from experimental values, of the order of 2 μmol kg⁻¹, are obtained. Handling editor: J. Melack     

Seasonal respiratory responses to temperature and hypoxia in relation to burrowing depth in three intertidal bivalves

Respiratory responses to temperature and hypoxia in relation to burrowing depth were determined for winter- (W-C) and summer-conditioned (S-C) individuals of , , and . These bivalves occur sympatrically on sand-flats but display different sediment burrowing depths (. , <2 cm; . , 3–8 cm; . , 5–20 cm). A range depths over which daily temperature variation and O₂ concentration decline rapidly from surface values. Species thermal tolerance limits were found to decrease and to be more greatly temperature compensated with burrowing depth. Oxygen consumption rate (VO₂ increased with temperature to 25°C in . , but was, thereafter, regulated (Q10 1.0) up to 40°C while VO₂ increased with temperature in . and . until thermally streased at 25° to 30°C. The deposit feeding . does not acclimate VO₂ to temperature while . and . , both suspension feeders, show “reverse” acclimation [VO₂ (W-C) < VO₂ (S-C)] that conserves overwintering energy stores. The shallow burrowing . and deposit feeding . rarely experience hypoxia and are poor to non-regulators of VO₂ in reduced O₂ concentrations. In contrast, when winter-conditioned, . is a moderate regulator of VO₂, the degree of regulation increasing in S-C individuals which are exposed to higher levels of hypoxia.