云杉种子萌发和幼苗生长对气候变暖与UV B辐射增强的响应

采用开顶式有机玻璃罩(OTCs)及紫外灯分别模拟气候变暖和UV-B增强,对位于气候变暖和UV-B增强突出的青藏高原东缘的高山峡谷地云杉种子萌发、幼苗生长和光合色素含量的变化进行测定分析,探讨云杉对气候变暖和UV-B增强的响应机理。结果显示:(1)UV-B辐射增强对云杉种子萌发无显著影响,但显著抑制萌发幼苗的生长、降低其针叶叶绿素含量,并造成幼苗大量死亡(P<0.05)。(2)气候变暖使云杉种子提前萌发,并提高了发芽势、发芽率和发芽指数,促进幼苗生长和叶绿素的积累,显著降低幼苗死亡率(P<0.05)。(3)气候变暖缓解了UV-B增强对云杉萌发幼苗生长和叶绿素含量的抑制作用,并降低了UV-B胁迫下幼苗的死亡率。研究表明,在未来气候变暖和UV-B辐射增强同时存在时,气候变暖能够在一定程度上缓解UV-B增强对云杉林早期更新带来的抑制作用。     

Responses of the Metabolism of the Larvae of Pocillopora damicornis to Ocean Acidification and Warming

Ocean acidification and warming are expected to threaten the persistence of tropical coral reef ecosystems. As coral reefs face multiple stressors, the distribution and abundance of corals will depend on the successful dispersal and settlement of coral larvae under changing environmental conditions. To explore this scenario, we used metabolic rate, at holobiont and molecular levels, as an index for assessing the physiological plasticity of Pocillopora damicornis larvae from this site to conditions of ocean acidity and warming. Larvae were incubated for 6 hours in seawater containing combinations of CO₂ concentration (450 and 950 µatm) and temperature (28 and 30°C). Rates of larval oxygen consumption were higher at elevated temperatures. In contrast, high CO₂ levels elicited depressed metabolic rates, especially for larvae released later in the spawning period. Rates of citrate synthase, a rate-limiting enzyme in aerobic metabolism, suggested a biochemical limit for increasing oxidative capacity in coral larvae in a warming, acidifying ocean. Biological responses were also compared between larvae released from adult colonies on the same day (cohorts). The metabolic physiology of Pocillopora damicornis larvae varied significantly by day of release. Additionally, we used environmental data collected on a reef in Moorea, French Polynesia to provide information about what adult corals and larvae may currently experience in the field. An autonomous pH sensor provided a continuous time series of pH on the natal fringing reef. In February/March, 2011, pH values averaged 8.075±0.023. Our results suggest that without adaptation or acclimatization, only a portion of naïve Pocillopora damicornis larvae may have suitable metabolic phenotypes for maintaining function and fitness in an end-of-the century ocean.     

Adaptive Capacity of the Habitat Modifying Sea Urchin Centrostephanus rodgersii to Ocean Warming and Ocean Acidification: Performance of Early Embryos

Background

Predicting effects of rapid climate change on populations depends on measuring the effects of climate stressors on performance, and potential for adaptation. Adaptation to stressful climatic conditions requires heritable genetic variance for stress tolerance present in populations.

Methodology/Principal Findings

We quantified genetic variation in tolerance of early development of the ecologically important sea urchin Centrostephanus rodgersii to near-future (2100) ocean conditions projected for the southeast Australian global change hot spot. Multiple dam-sire crosses were used to quantify the interactive effects of warming (+2–4°C) and acidification (−0.3−0.5 pH units) across twenty-seven family lines. Acidification, but not temperature, decreased the percentage of cleavage stage embryos. In contrast, temperature, but not acidification decreased the percentage of gastrulation. Cleavage success in response to both stressors was strongly affected by sire identity. Sire and dam identity significantly affected gastrulation and both interacted with temperature to determine developmental success. Positive genetic correlations for gastrulation indicated that genotypes that did well at lower pH also did well in higher temperatures.

Conclusions/Significance

Significant genotype (sire) by environment interactions for both stressors at gastrulation indicated the presence of heritable variation in thermal tolerance and the ability of embryos to respond to changing environments. The significant influence of dam may be due to maternal provisioning (maternal genotype or environment) and/or offspring genotype. It appears that early development in this ecologically important sea urchin is not constrained in adapting to the multiple stressors of ocean warming and acidification. The presence of tolerant genotypes indicates the potential to adapt to concurrent warming and acidification, contributing to the resilience of C. rodgersii in a changing ocean.     

Ocean Acidification Alters the Photosynthetic Responses of a Coccolithophorid to Fluctuating Ultraviolet and Visible Radiation

Mixing of seawater subjects phytoplankton to fluctuations in photosynthetically active radiation (400–700 nm) and ultraviolet radiation (UVR; 280–400 nm). These irradiance fluctuations are now superimposed upon ocean acidification and thinning of the upper mixing layer through stratification, which alters mixing regimes. Therefore, we examined the photosynthetic carbon fixation and photochemical performance of a coccolithophore, Gephyrocapsa oceanica, grown under high, future (1,000 μatm) and low, current (390 μatm) CO₂ levels, under regimes of fluctuating irradiances with or without UVR. Under both CO₂ levels, fluctuating irradiances, as compared with constant irradiance, led to lower nonphotochemical quenching and less UVR-induced inhibition of carbon fixation and photosystem II electron transport. The cells grown under high CO₂ showed a lower photosynthetic carbon fixation rate but lower nonphotochemical quenching and less ultraviolet B (280–315 nm)-induced inhibition. Ultraviolet A (315–400 nm) led to less enhancement of the photosynthetic carbon fixation in the high-CO₂-grown cells under fluctuating irradiance. Our data suggest that ocean acidification and fast mixing or fluctuation of solar radiation will act synergistically to lower carbon fixation by G. oceanica, although ocean acidification may decrease ultraviolet B-related photochemical inhibition.The oceans absorb about 25 million tons of CO₂ per day from the atmosphere (Sabine et al., 2004), leading to the acidification of seawater in surface oceans. The pH of oceanic surface seawater will decline by 0.3 to 0.4 units, reflecting a 100% to 150% increase in [H⁺], by the year 2100 under “a fossil-fuel intensive” emission scenario (Houghton, 2001). This ocean acidification and the associated chemical changes may bring about critical ecological and social consequences (Turley et al., 2010).Coccolithophores, as a key group of oceanic primary producers, with coccolith scales made of CaCO₃, are important to global carbon cycles (Riebesell and Tortell, 2011). Ocean acidification generally decreases calcification by coccolithophores (Riebesell et al., 2000; Zondervan et al., 2002; Delille et al., 2005; Beaufort et al., 2011) and other calcifying algae (Gao and Zheng, 2010; Sinutok et al., 2011), with responses differing across species or different environmental conditions (Langer et al., 2006, 2009; Iglesias-Rodriguez et al., 2008; Doney et al., 2009; Shi et al., 2009). Algal calcification, in turn, influences the impacts of solar ultraviolet radiation (UVR; 280–400 nm) on the algae’s photophysiology (Gao et al., 2009; Gao and Zheng, 2010; Guan and Gao, 2010).Although the Montreal Protocol has resulted in a slowing of ozone depletion, ultraviolet B (UVB) irradiance (280–315 nm) reaching northern temperate regions increased 10% between 1983 and 2003 (Josefsson, 2006), and a recent observation found an ozone hole above the Arctic (Manney et al., 2011), reflecting ongoing impacts of climate change on ozone depletion. Biologically significant levels of UVR reach as deep as 80 m in pelagic oceans (Smith et al., 1992). In coastal waters or areas with high productivity, UVB irradiance usually penetrates only a few meters due to the attenuation caused by suspended particles and dissolved organic matter (Hargreaves, 2003; Tedetti and Sempéré, 2006). Ultraviolet A (UVA) and photosynthetically active radiation (PAR) are also attenuated but penetrate to much deeper depths due to their wavelength properties and intensities. UVA and UVB can both act synergistically with ocean acidification to inhibit algal photosynthetic performance (Gao et al., 2009), and the inhibition caused by UVB could be about 2.5 times that caused by UVA (Gao and Zheng, 2010); however, an antagonistic effect of UVB and ocean acidification was also found in a diatom (Li et al., 2012).In parallel, global warming due to increased atmospheric CO₂ concentration causes ocean warming, which results in a decrease in the depth of the upper mixing layer (UML; Sarmiento et al., 2004). Such stratification increases integrated exposures of phytoplankton cells within the UML to solar UVR and visible radiation and decreases the upward transport of nutrients from deeper water layers, influencing phytoplankton photophysiology (Beardall et al., 2009; Gao et al., 2012a). Fluctuations of both solar PAR and UVR within the UML affect phytoplankton photosynthetic activity and carbon fixation (Helbling et al., 2003; Villafañe et al., 2007; Guan and Gao, 2008; Dimier et al., 2009). Mixing depths and/or mixing rates in the upper oceans also change in response to increased stratification and/or wind speed due to global climate change (Sarmiento et al., 2004; Boyd et al., 2010).Phytoplankton responses to fluctuating solar radiation vary, particularly if considered in combination with other environmental factors, due to antagonistic or synergistic interactions. Fluctuation of solar radiation on cloudy days led to higher primary production in the presence of UVA (315–400 nm) as compared with the presence of UVA on sunny days (Gao et al., 2007). Algal acclimation to fluctuating irradiance can lead to differences in growth rates and cellular pigment content compared with the cells acclimated to constant irradiance (Van de Poll et al., 2007, 2010). On the other hand, the mixing rate in the UML is strongly controlled by wind (Denman and Gargett, 1983; MacIntyre, 1993), which may increase due to global warming (Toggweiler and Russell, 2008). Therefore, changes in mixing rate and stratification may interact with ocean acidification to affect the photophysiology of phytoplankton. Nevertheless, to our knowledge, nothing has yet been documented on the combined impacts of the fluctuation of PAR or UVR and ocean acidification on the photosynthetic performance of coccolithophores.Under this scenario, we expect that the photosynthesis of coccolithophores will respond differentially to fluctuating PAR, with or without UVR, when grown under ocean acidification conditions, since the balance of high PAR- or UVR-induced damage and the counteracting repair could differ under elevated CO₂ or acidity. To test these interactions, we grew Gephyrocapsa oceanica, which is widely distributed in temperate and tropical waters (Okabe, 1997), under current and ocean acidification conditions and examined its photochemical activity and photosynthesis under different combinations of fluctuating PAR and UVR.     

云杉幼苗对气候变暖和UV-B辐射增强的光合响应

采用开顶式有机玻璃罩(OTCs)及紫外灯分别模拟气候变暖和紫外辐射B(UV-B)增强,对位于气候变暖和UV-B增强突出的青藏高原东缘、高山峡谷地云杉(Picea asperata)幼苗的光合气体交换和叶绿素荧光参数进行测定分析,探讨云杉幼苗对气候变暖和UV-B增强的光合响应特性。结果显示:(1)UV-B辐射增强显著抑制了云杉幼苗茎和根的伸长生长以及生物量的累积,显著降低了云杉幼苗的净光合速率(Pn)、最大光合速率(Pmax)和表观量子产量(Φ),但是提高了光补偿点(LCP);UV-B辐射增强导致了云杉幼苗光合系统Ⅱ(PSⅡ)的光抑制,使PSⅡ有效量子产量(ΦPSⅡ)显著降低。(2)单纯OTC模拟增温显著提高了云杉幼苗的Pn和Pmax,而对气孔导度(Gs)、蒸腾速率(Tr)和Φ无显著影响。(3)模拟增温缓解了UV-B增强对云杉幼苗光合作用的抑制作用,显著提高了UV-B胁迫下幼苗的Pn、Pmax、PSⅡ的潜在量子效率(Fv/Fm)和有效量子产量(ΦPSⅡ),并且提高了UV-B胁迫下幼苗茎、根的生长以及生物量的累积。研究表明,在未来气候变暖和UV-B辐射增强同时存在时,气候变暖能够在一定程度上缓解UV-B增强对云杉林光合作用的抑制作用。     

Development in the Floating World: Defenses of Eggs and Embryos Against Damage from UV Radiation

Eggs and embryos of many aquatic organisms develop in the watercolumn and can experience ultraviolet radiation with potentiallydeleterious effects. This is especially vexing for floatingembryos that develop in the surface or neuston layer. Radiationdamage can be a particular problem for these embryos since thecell division cycle during the cleavage period is quite shortand often these cycles do not have mitotic checkpoints to insurefaithful transmission of DNA to the daughter cells. This couldresult in cell division with unrepaired DNA in the blastomeres,which could impact embryogenesis and the transmission of thegenome through the germ line. Described strategies to restrictradiation damage include mechanisms to limit oxidative damageand the use of sunscreens such as the mycosporines to curb radiationto sensitive targets. We describe a particularly ingenious useof sunscreens in the tunicate embryo, the use of extra-embryoniccells to shield the embryo from potentially harmful UV-A andUV-B radiation. We also raise questions regarding the natureof UV damage to embryos (is it DNA or also protein) and thecharacteristics of DNA repair in such embryos. It is likelythat unique mechanisms are present in floating embryos thatdevelop in this air-water interface to assure that cell andgenomic integrity are maintained in this challenging environment.     

Long-Term Responses of the Endemic Reef-Builder Cladocora caespitosa to Mediterranean Warming

Recurrent climate-induced mass-mortalities have been recorded in the Mediterranean Sea over the past 15 years. Cladocora caespitosa, the sole zooxanthellate scleractinian reef-builder in the Mediterranean, is among the organisms affected by these episodes. Extensive bioconstructions of this endemic coral are very rare at the present time and are threatened by several stressors. In this study, we assessed the long-term response of this temperate coral to warming sea-water in the Columbretes Islands (NW Mediterranean) and described, for the first time, the relationship between recurrent mortality events and local sea surface temperature (SST) regimes in the Mediterranean Sea. A water temperature series spanning more than 20 years showed a summer warming trend of 0.06°C per year and an increased frequency of positive thermal anomalies. Mortality resulted from tissue necrosis without massive zooxanthellae loss and during the 11-year study, necrosis was recorded during nine summers separated into two mortality periods (2003–2006 and 2008–2012). The highest necrosis rates were registered during the first mortality period, after the exceptionally hot summer of 2003. Although necrosis and temperature were significantly associated, the variability in necrosis rates during summers with similar thermal anomalies pointed to other acting factors. In this sense, our results showed that these differences were more closely related to the interannual temperature context and delayed thermal stress after extreme summers, rather than to acclimatisation and adaption processes.     

Responses of the Emiliania huxleyi Proteome to Ocean Acidification

Ocean acidification due to rising atmospheric CO₂ is expected to affect the physiology of important calcifying marine organisms, but the nature and magnitude of change is yet to be established. In coccolithophores, different species and strains display varying calcification responses to ocean acidification, but the underlying biochemical properties remain unknown. We employed an approach combining tandem mass-spectrometry with isobaric tagging (iTRAQ) and multiple database searching to identify proteins that were differentially expressed in cells of the marine coccolithophore species Emiliania huxleyi (strain NZEH) between two CO₂ conditions: 395 (∼current day) and ∼1340 p.p.m.v. CO₂. Cells exposed to the higher CO₂ condition contained more cellular particulate inorganic carbon (CaCO₃) and particulate organic nitrogen and carbon than those maintained in present-day conditions. These results are linked with the observation that cells grew slower under elevated CO₂, indicating cell cycle disruption. Under high CO₂ conditions, coccospheres were larger and cells possessed bigger coccoliths that did not show any signs of malformation compared to those from cells grown under present-day CO₂ levels. No differences in calcification rate, particulate organic carbon production or cellular organic carbon: nitrogen ratios were observed. Results were not related to nutrient limitation or acclimation status of cells. At least 46 homologous protein groups from a variety of functional processes were quantified in these experiments, of which four (histones H2A, H3, H4 and a chloroplastic 30S ribosomal protein S7) showed down-regulation in all replicates exposed to high CO₂, perhaps reflecting the decrease in growth rate. We present evidence of cellular stress responses but proteins associated with many key metabolic processes remained unaltered. Our results therefore suggest that this E. huxleyi strain possesses some acclimation mechanisms to tolerate future CO₂ scenarios, although the observed decline in growth rate may be an overriding factor affecting the success of this ecotype in future oceans.     

Ocean Warming and Spread of Pathogenic Vibrios in the Aquatic Environment

Vibrios are among the most common bacteria that inhabit surface waters throughout the world and are responsible for a number of severe infections both in humans and animals. Several reports recently showed that human Vibrio illnesses are increasing worldwide including fatal acute diarrheal diseases, such as cholera, gastroenteritis, wound infections, and septicemia. Many scientists believe this increase may be associated with global warming and rise in sea surface temperature (SST), although not enough evidence is available to support a causal link between emergence of Vibrio infections and climate warming. The effect of increased SST in promoting spread of vibrios in coastal and brackish waters is considered a causal factor explaining this trend. Field and laboratory studies carried out over the past 40 years supported this hypothesis, clearly showing temperature promotes Vibrio growth and persistence in the aquatic environment. Most recently, a long-term retrospective microbiological study carried out in the coastal waters of the southern North Sea provided the first experimental evidence for a positive and significant relationship between SST and Vibrio occurrence over a multidecadal time scale. As a future challenge, macroecological studies of the effects of ocean warming on Vibrio persistence and spread in the aquatic environment over large spatial and temporal scales would conclusively support evidence acquired to date combined with studies of the impact of global warming on epidemiologically relevant variables, such as host susceptibility and exposure. Assessing a causal link between ongoing climate change and enhanced growth and spread of vibrios and related illness is expected to improve forecast and mitigate future outbreaks associated with these pathogens.     

Study of the Response of a Biofilm Bacterial Community to UV Radiation

We have developed a bioluminescent whole-cell biosensor that can be incorporated into biofilm ecosystems. RM4440 is a Pseudomonas aeruginosa FRD1 derivative that carries a plasmid-based recA-luxCDABE fusion. We immobilized RM4440 in an alginate matrix to simulate a biofilm, and we studied its response to UV radiation damage. The biofilm showed a protective property by physical shielding against UV C, UV B, and UV A. Absorption of UV light by the alginate matrix translated into a higher survival rate than observed with planktonic cells at similar input fluences. UV A was shown to be effectively blocked by the biofilm matrix and to have no detectable effects on cells contained in the biofilm. However, in the presence of photosensitizers (i.e., psoralen), UV A was effective in inducing light production and cell death. RM4440 has proved to be a useful tool to study microbial communities in a noninvasive manner.     

Preliminary Evidence for the Amplification of Global Warming in Shallow,Intertidal Estuarine Waters

Over the past 50 years, mean annual water temperature in northeastern U.S. estuaries has increased by approximately 1.2°C, with most of the warming recorded in the winter and early spring. A recent survey and synthesis of data from four locations in Southern Rhode Island has led us to hypothesize that this warming may be amplified in the shallow (<1 m), nearshore portions of these estuaries. While intertidal areas are not typically selected as locations for long-term monitoring, we compiled data from published literature, theses, and reports that suggest that enhanced warming may be occurring, perhaps at rates three times higher than deeper estuarine waters. Warmer spring waters may be one of the factors influencing biota residing in intertidal regions both in general as well as at our specific sites. We observed greater abundance of fish, and size of Menidia sp., in recent (2010–2012) seine surveys compared to similar collections in 1962. While any linkages are speculative and data are preliminary, taken together they suggest that shallow intertidal portions of estuaries may be important places to look for the effects of climate change.     

森林凋落物动态及其对全球变暖的响应

综述了森林凋落物研究的进展,森林凋落物动态的研究随研究方法的改进而不断深化。制约凋落物分解速率的因素有内在因素即凋落物自身的化学物理性质和外在因素即凋落物分解过程发生的外部环境条件,如参与分解的异养微生物和土壤动物群落的种类、数量、活性（生物类因素）和气候、土壤、大气成分等（非生物类因素）。讨论了全球变暖可能引起的凋落物量和凋落物分解的变化。气温上升可能引发植被分布、物候特征和制约凋落物分解因素的改变,影响森林凋落物动态,最终影响森林生态系统物质循环的功能。     

Sensitivity and Acclimation of Three Canopy-Forming Seaweeds to UVB Radiation and Warming

Canopy-forming seaweeds, as primary producers and foundation species, provide key ecological services. Their responses to multiple stressors associated with climate change could therefore have important knock-on effects on the functioning of coastal ecosystems. We examined interactive effects of UVB radiation and warming on juveniles of three habitat-forming subtidal seaweeds from Western Australia–Ecklonia radiata, Scytothalia dorycarpa and Sargassum sp. Fronds were incubated for 14 days at 16–30°C with or without UVB radiation and growth, health status, photosynthetic performance, and light absorbance measured. Furthermore, we used empirical models from the metabolic theory of ecology to evaluate the sensitivity of these important seaweeds to ocean warming. Results indicated that responses to UVB and warming were species specific, with Sargassum showing highest tolerance to a broad range of temperatures. Scytothalia was most sensitive to elevated temperature based on the reduced maximum quantum yields of PSII; however, Ecklonia was most sensitive, according to the comparison of activation energy calculated from Arrhenius’ model. UVB radiation caused reduction in the growth, physiological responses and thallus health in all three species. Our findings indicate that Scytothalia was capable of acclimating in response to UVB and increasing its light absorption efficiency in the UV bands, probably by up-regulating synthesis of photoprotective compounds. The other two species did not acclimate over the two weeks of exposure to UVB. Overall, UVB and warming would severely inhibit the growth and photosynthesis of these canopy-forming seaweeds and decrease their coverage. Differences in the sensitivity and acclimation of major seaweed species to temperature and UVB may alter the balance between species in future seaweed communities under climate change.     

Soil Microbial Community Responses to a Decade of Warming as Revealed by Comparative Metagenomics

Soil microbial communities are extremely complex, being composed of thousands of low-abundance species (<0.1% of total). How such complex communities respond to natural or human-induced fluctuations, including major perturbations such as global climate change, remains poorly understood, severely limiting our predictive ability for soil ecosystem functioning and resilience. In this study, we compared 12 whole-community shotgun metagenomic data sets from a grassland soil in the Midwestern United States, half representing soil that had undergone infrared warming by 2°C for 10 years, which simulated the effects of climate change, and the other half representing the adjacent soil that received no warming and thus, served as controls. Our analyses revealed that the heated communities showed significant shifts in composition and predicted metabolism, and these shifts were community wide as opposed to being attributable to a few taxa. Key metabolic pathways related to carbon turnover, such as cellulose degradation (∼13%) and CO₂ production (∼10%), and to nitrogen cycling, including denitrification (∼12%), were enriched under warming, which was consistent with independent physicochemical measurements. These community shifts were interlinked, in part, with higher primary productivity of the aboveground plant communities stimulated by warming, revealing that most of the additional, plant-derived soil carbon was likely respired by microbial activity. Warming also enriched for a higher abundance of sporulation genes and genomes with higher G+C content. Collectively, our results indicate that microbial communities of temperate grassland soils play important roles in mediating feedback responses to climate change and advance the understanding of the molecular mechanisms of community adaptation to environmental perturbations.     

Responses of Plant Community Composition and Biomass Production to Warming and Nitrogen Deposition in a Temperate Meadow Ecosystem

Climate change has profound influences on plant community composition and ecosystem functions. However, its effects on plant community composition and biomass production are not well understood. A four-year field experiment was conducted to examine the effects of warming, nitrogen (N) addition, and their interactions on plant community composition and biomass production in a temperate meadow ecosystem in northeast China. Experimental warming had no significant effect on plant species richness, evenness, and diversity, while N addition highly reduced the species richness and diversity. Warming tended to reduce the importance value of graminoid species but increased the value of forbs, while N addition had the opposite effect. Warming tended to increase the belowground biomass, but had an opposite tendency to decrease the aboveground biomass. The influences of warming on aboveground production were dependent upon precipitation. Experimental warming had little effect on aboveground biomass in the years with higher precipitation, but significantly suppressed aboveground biomass in dry years. Our results suggest that warming had indirect effects on plant production via its effect on the water availability. Nitrogen addition significantly increased above- and below-ground production, suggesting that N is one of the most important limiting factors determining plant productivity in the studied meadow steppe. Significant interactive effects of warming plus N addition on belowground biomass were also detected. Our observations revealed that environmental changes (warming and N deposition) play significant roles in regulating plant community composition and biomass production in temperate meadow steppe ecosystem in northeast China.     

Warming Ocean Conditions Relate to Increased Trophic Requirements of Threatened and Endangered Salmon

The trophic habits, size and condition of yearling Chinook salmon (Oncorhynchus tshawytscha) caught early in their marine residence were examined during 19 survey years (1981–1985; 1998–2011). Juvenile salmon consumed distinct highly piscivorous diets in cold and warm ocean regimes with major differences between ocean regimes driven by changes in consumption of juvenile rockfishes, followed by several other fish prey, adult euphausiids and decapod larvae. Notable, Chinook salmon consumed 30% more food in the warm versus cold ocean regime in both May and June. Additionally, there were about 30% fewer empty stomachs in the warm ocean regime in May, and 10% fewer in warm June periods. The total prey energy density consumed during the warmer ocean regime was also significantly higher than in cold. Chinook salmon had lower condition factor and were smaller in fork length during the warm ocean regime, and were longer and heavier for their size during the cold ocean regime. The significant increase in foraging during the warm ocean regime occurred concurrently with lower available prey biomass. Adult return rates of juvenile Chinook salmon that entered the ocean during a warm ocean regime were lower. Notably, our long term data set contradicts the long held assertion that juvenile salmon eat less in a warm ocean regime when low growth and survival is observed, and when available prey are reduced. Comparing diet changes between decades under variable ocean conditions may assist us in understanding the effects of projected warming ocean regimes on juvenile Chinook salmon and their survival in the ocean environment. Bioenergetically, the salmon appear to require more food resources during warm ocean regimes.     

Potential Impacts of a Western Pacific Grapsid Crab on Intertidal Communities of the Northwestern Atlantic Ocean

Population density and size distribution, salinity tolerance, and feeding activity were examined in a western Pacific grapsid crab, Hemigrapsus sanguineus, that was recently introduced to the mid-Atlantic coast of North America. Seasonal abundance on a boulder/cobble shore (Crane Neck Pt.) in central Long Island Sound, New York, USA, during 1997–1998, ranged from 7 to 10 crabs m⁻² averaged over the entire intertidal zone. Crabs occurred throughout the intertidal during summer and fall, but appeared to move from high to low elevations during winter. In laboratory experiments, H. sanguineus tolerated salinity down to 10 ppt for 7 d, but showed significant preference for 20 or 27 ppt over 10 ppt. The crabs readily consumed juvenile snails (Littorina littorea) and mussels (Mytilus edulis), as well as other common species of macroalgae and invertebrates occurring at Crane Neck Pt. High feeding rates and the ability to consume littorine snails up to 13 mm in height and mussels up to 20 mm in length suggest that this nonindigenous species has the potential to significantly affect the structure of rocky intertidal communities in the northwestern Atlantic Ocean; however, rigorous field studies are needed to accurately determine the impact of this recent introduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Responses of Soil Microbial Communities to Experimental Warming in Alpine Grasslands on the Qinghai-Tibet Plateau

Global surface temperature is predicted to increase by at least 1.5°C by the end of this century. However, the response of soil microbial communities to global warming is still poorly understood, especially in high-elevation grasslands. We therefore conducted an experiment on three types of alpine grasslands on the Qinghai-Tibet Plateau to study the effect of experimental warming on abundance and composition of soil microbial communities at 0–10 and 10–20 cm depths. Plots were passively warmed for 3 years using open-top chambers and compared to adjacent control plots at ambient temperature. Soil microbial communities were assessed using phospholipid fatty acid (PLFA) analysis. We found that 3 years of experimental warming consistently and significantly increased microbial biomass at the 0–10 cm soil depth of alpine swamp meadow (ASM) and alpine steppe (AS) grasslands, and at both the 0–10 and 10–20 cm soil depths of alpine meadow (AM) grasslands, due primarily to the changes in soil temperature, moisture, and plant coverage. Soil microbial community composition was also significantly affected by warming at the 0–10 cm soil depth of ASM and AM and at the 10–20 cm soil depth of AM. Warming significantly decreased the ratio of fungi to bacteria and thus induced a community shift towards bacteria at the 0–10 cm soil depth of ASM and AM. While the ratio of arbuscular mycorrhizal fungi to saprotrophic fungi (AMF/SF) was significantly decreased by warming at the 0–10 cm soil depth of ASM, it was increased at the 0–10 cm soil depth of AM. These results indicate that warming had a strong influence on soil microbial communities in the studied high-elevation grasslands and that the effect was dependent on grassland type.     

Responses of Two Scleractinian Corals to Cobalt Pollution and Ocean Acidification

The effects of ocean acidification alone or in combination with warming on coral metabolism have been extensively investigated, whereas none of these studies consider that most coral reefs near shore are already impacted by other natural anthropogenic inputs such as metal pollution. It is likely that projected ocean acidification levels will aggravate coral reef health. We first investigated how ocean acidification interacts with one near shore locally abundant metal on the physiology of two major reef-building corals: Stylophora pistillata and Acropora muricata. Two pH levels (pH_T 8.02; pCO₂ 366 μatm and pH_T 7.75; pCO₂ 1140 μatm) and two cobalt concentrations (natural, 0.03 μg L^-1 and polluted, 0.2 μg L^-1) were tested during five weeks in aquaria. We found that, for both species, cobalt input decreased significantly their growth rates by 28% while it stimulated their photosystem II, with higher values of rETR_max (relative Electron Transport Rate). Elevated pCO₂ levels acted differently on the coral rETR_max values and did not affect their growth rates. No consistent interaction was found between pCO₂ levels and cobalt concentrations. We also measured in situ the effect of higher cobalt concentrations (1.06 ± 0.16 μg L^-1) on A. muricata using benthic chamber experiments. At this elevated concentration, cobalt decreased simultaneously coral growth and photosynthetic rates, indicating that the toxic threshold for this pollutant has been reached for both host cells and zooxanthellae. Our results from both aquaria and in situ experiments, suggest that these coral species are not particularly sensitive to high pCO₂ conditions but they are to ecologically relevant cobalt concentrations. Our study reveals that some reefs may be yet subjected to deleterious pollution levels, and even if no interaction between pCO₂ levels and cobalt concentration has been found, it is likely that coral metabolism will be weakened if they are subjected to additional threats such as temperature increase, other heavy metals, and eutrophication.