Posts Tagged 'otherprocess'

Combined effects of ocean acidification and increased light intensity on natural phytoplankton communities from two Southern Ocean water masses

The composition of phytoplankton communities plays a major role in the efficiency of the biological carbon pump and energy transfer to higher trophic levels. Phytoplankton community composition can be significantly affected by changes in environmental conditions. We investigated the effect of increased pCO2 and light intensity on natural communities from two Southern Ocean water masses, the Subtropical Frontal Zone (STFZ) and Subantarctic Surface Waters (SASW). The community in both experiments shifted to predominately dinoflagellates under high pCO2 and high light and the community composition was significantly different between both treatments at the end of the incubation. In the STFZ assemblage, the combination of increased light and pCO2 had a small positive effect on diatom, coccolithophores and picoeukaryote abundance at the beginning of the experiment while higher pCO2 alone had no or a negative effect. In the SASW assemblage, the combination of increased light and pCO2 had a negative effect on diatom abundance while lower pH/higher pCO2 alone resulted in an increase in diatom counts compared to the control. Coccolithophores grew only in the control treatment. Our results show that there are taxon-specific and locality specific differences in natural phytoplankton community responses to increased light and pCO2 within low nutrient regions.

Continue reading ‘Combined effects of ocean acidification and increased light intensity on natural phytoplankton communities from two Southern Ocean water masses’

Transgenerational exposure to ocean acidification induces biochemical distress in a keystone amphipod species (Gammarus locusta)

Highlights

  • A transgenerational ocean acidification exposure was performed in Gammarus locusta
  • Biomarkers of cellular damage, protein repair and oxidative stress were quantified
  • Within- and transgenerational oxidative damage occurred under high CO2
  • Oxidative stress in F0-proteome may impair offspring’ DNA efficiency repair system
  • Increased vulnerability of wild G. locusta populations under ocean acidification

Abstract

Atmospheric carbon dioxide (CO2) levels are increasing at the fastest rate ever recorded, causing higher CO2 dissolution in the ocean, leading to a process known as ocean acidification (OA). Unless anthropogenic CO2 emissions are reduced, they are expected to reach ~900 ppm by the century’s end, resulting in a 0.13-0.42 drop in the seawater pH levels. Since the transgenerational effects of high CO2 in marine organisms are still poorly understood at lower levels of biological organization (namely at the biochemical level), here we reared a key ecological relevant marine amphipod, Gammarus locusta, under control and high CO2 conditions for two generations. We measured several stress-related biochemical endpoints: i) oxidative damage [lipid peroxidation (LPO) and DNA damage]; ii) protein repair and removal mechanisms [heat shock proteins (HSPs) and ubiquitin (Ub)]; as well as iii) antioxidant responses [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione s-transferase (GST)] and total antioxidant capacity (TAC). The present results support the premise that exposure to high CO2 is expected to decrease survival rates in this species and cause within- and transgenerational oxidative damage. More specifically, the predicted upsurge of reactive oxygen and nitrogen species seemed to overwhelm the stimulated amphipod antioxidant machinery, which proved insufficient in circumventing protein damage within the parents. Additionally, negative effects of OA are potentially being inherited by the offspring, since the oxidative stress imposed in the parent’s proteome appears to be restricting DNA repair mechanisms efficiency within the offspring’s. Thus, we argue that a transgenerational exposure of G. locusta could further increase vulnerability to OA and may endanger the fitness and sustainability of natural populations.

Continue reading ‘Transgenerational exposure to ocean acidification induces biochemical distress in a keystone amphipod species (Gammarus locusta)’

Role of host genetics and heat tolerant algal symbionts in sustaining populations of the endangered coral Orbicella faveolata in the Florida Keys with ocean warming

Identifying which factors lead to coral bleaching resistance is a priority given the global decline of coral reefs with ocean warming. During the second year of back‐to‐back bleaching events in the Florida Keys in 2014 and 2015, we characterized key environmental and biological factors associated with bleaching resilience in the threatened reef‐building coral Orbicella faveolata. Ten reefs (five inshore, five offshore, 179 corals total) were sampled during bleaching (September 2015) and recovery (May 2016). Corals were genotyped with 2bRAD and profiled for algal symbiont abundance and type. O. faveolata at the inshore sites, despite higher temperatures, demonstrated significantly higher bleaching resistance and better recovery compared to offshore. The thermotolerant Durusdinium trenchii (formerly Symbiondinium trenchii) was the dominant endosymbiont type region‐wide during initial (78.0% of corals sampled) and final (77.2%) sampling; > 90% of the non‐bleached corals were dominated by D. trenchii. 2bRAD host genotyping found no genetic structure among reefs, but inshore sites showed a high level of clonality. While none of the measured environmental parameters were correlated with bleaching, 71% of variation in bleaching resistance and 73% of variation in the proportion of D. trenchii was attributable to differences between genets, highlighting the leading role of genetics in shaping natural bleaching patterns. Notably, D. trenchii was rarely dominant in O. faveolata from the Florida Keys in previous studies, even during bleaching. The region‐wide high abundance of D. trenchii was likely driven by repeated bleaching associated with the two warmest years on record for the Florida Keys (2014 and 2015). On inshore reefs in the upper Florida Keys, O. faveolata was most abundant, had the highest bleaching resistance, and contained the most corals dominated by D. trenchii, illustrating a causal link between heat tolerance and ecosystem resilience with global change.

Continue reading ‘Role of host genetics and heat tolerant algal symbionts in sustaining populations of the endangered coral Orbicella faveolata in the Florida Keys with ocean warming’

Effects of ocean acidification on the transcriptome of larval Atlantic cod and impacts of parental acclimation

Ocean acidification, caused by the uptake of carbon dioxide (CO2) from the atmosphere, is impacting many marine organisms. This dissertation investigated the effects of direct exposure and parental acclimation to simulated ocean acidification on the larval stages of Atlantic cod (Gadus morhua, L.). For this, ocean acidification levels predicted for the year 2100 were applied on cod eggs from hatch to 36 days post hatch in in vivo laboratory experiments. The direct exposure experiment clearly showed that Atlantic cod larvae were severely affected by simulated ocean acidification on a phenotypic level (chapter 1). Changes in growth, bone and gill development as well as increased frequency of organ damages were observed under predicted ocean acidification levels compared to controls. Then, the underlying molecular phenotype was assessed, using whole transcriptome sequencing (RNA-Seq), to couple transcriptomic mechanisms to the observed phenotypes (chapter 2). Transcriptome analysis revealed 1413 differentially expressed genes in late larval stages, corresponding to the observed changes in growth and developmental patterns, leading to the conclusion that these changes represent an accelerated development under ocean acidification. Surprisingly, only few genes (3 and 16, respectively) were differentially expressed in the early larval stages. An experiment set to address the effects of long-term parental acclimation (5 month) was performed to assess whether or not this kind of acclimation can mediate the identified detrimental direct effects on the larvae (chapter 3). However, none of the previously observed phenotypes under ocean acidification were found in this experiment, making it impossible to draw any conclusion on the effectiveness of parental acclimation on larval susceptibility to simulated ocean acidification. A concluding meta-analysis between experiments shows that the larvae of Atlantic Cod are to be considered vulnerable to simulated ocean acidification.

Continue reading ‘Effects of ocean acidification on the transcriptome of larval Atlantic cod and impacts of parental acclimation’

Impact of increased seawater pCO2 on the host and symbiotic algae of juvenile giant clam Tridacna crocea

Increases in atmospheric CO2 cause decreases in calcium carbonate saturation, which is predicted to affect the calcification process of most marine calcifiers. At the same time, the increase of seawater pCO2 is also known to increase the productivity of primary producers. Giant clams host symbiotic dinoflagellates (‘zooxanthellae’: Symbiodinium spp.) that provide nutrition and use CO2 as their primary source for photosynthesis. This leads to the hypothesis that increased seawater pCO2 rise could positively affect the production of giant clam zooxanthellae, and dampen effects of CO2 on host giant clams. To test this hypothesis, we measured the shell growth rate, photosynthesis rate, respiration rate and zooxanthellae density of the juvenile Tridacna crocea reared under three different pCO2 conditions. Results revealed that negative shell growth of juvenile Tridacna crocea was observed once seawater Ωarag reached less than 2.33. Additionally, although zooxanthellae density in T. crocea increased with seawater pCO2 rise, zooxanthellae productivity did not change, suggesting that the productivity per zooxanthella decreased in high pCO2 seawater. Our findings suggest future seawater pCO2 rise will not increase productivity of zooxanthellae, thus giant clam will be negatively impacted in the coming centuries.

Continue reading ‘Impact of increased seawater pCO2 on the host and symbiotic algae of juvenile giant clam Tridacna crocea’

El Niño-related thermal stress coupled with upwelling-related ocean acidification negatively impacts cellular to population-level responses in pteropods along the California Current System with implications for increased bioenergetic costs

Understanding the interactive effects of multiple stressors on pelagic mollusks associated with global climate change is especially important in highly productive coastal ecosystems of the upwelling regime, such as the California Current System (CCS). Due to temporal overlap between a marine heatwave, an El Niño event, and springtime intensification of the upwelling, pteropods of the CCS were exposed to co-occurring increased temperature, low Ωar and pH, and deoxygenation. The variability in the natural gradients during NOAA’s WCOA 2016 cruise provided a unique opportunity for synoptic study of chemical and biological interactions. We investigated the effects of in situ multiple drivers and their interactions across cellular, physiological, and population levels. Oxidative stress biomarkers were used to assess pteropods’ cellular status and antioxidant defenses. Low aragonite saturation state (Ωar) is associated with significant activation of oxidative stress biomarkers, as indicated by increased levels of lipid peroxidation (LPX), but the antioxidative activity defense might be insufficient against cellular stress. Thermal stress in combination with low Ωar additively increases the level of LPX toxicity, while food availability can mediate the negative effect. On the physiological level, we found synergistic interaction between low Ωar and deoxygenation and thermal stress (Ωar:T, O2:T). On the population level, temperature was the main driver of abundance distribution, with low Ωar being a strong driver of secondary importance. The additive effects of thermal stress and low Ωar on abundance suggest a negative effect of El Niño at the population level. Our study clearly demonstrates Ωar and temperature are master variables in explaining biological responses, cautioning the use of a single parameter in the statistical analyses. High quantities of polyunsaturated fatty acids are susceptible to oxidative stress because of LPX, resulting in the loss of lipid reserves and structural damage to cell membranes, a potential mechanism explaining extreme pteropod sensitivity to low Ωar. Accumulation of oxidative damage requires metabolic compensation, implying energetic trade-offs under combined thermal and low Ωar and pH stress. Oxidative stress biomarkers can be used as early-warning signal of multiple stressors on the cellular level, thereby providing important new insights into factors that set limits to species’ tolerance to in situ multiple drivers.

Continue reading ‘El Niño-related thermal stress coupled with upwelling-related ocean acidification negatively impacts cellular to population-level responses in pteropods along the California Current System with implications for increased bioenergetic costs’

Low and variable pH decreases recruitment efficiency in populations of a temperate coral naturally present at a CO2 vent

Atmospheric carbon dioxide enrichment alters seawater carbonate chemistry, thus threatening calcifying organisms such as corals. Coral populations at carbon dioxide vents are natural acidification experiments that mimic organism responses to seawater pH values projected for 2100. Even if demographic traits are paramount information to assess ecological relationships and habitat suitability, population dynamics studies on corals thriving under acidified conditions are lacking. Here, we investigate the demography and reproduction of populations of the solitary, symbiotic, temperate coral Balanophyllia europaea naturally living along a pH gradient at a Mediterranean CO2 vent. Gametogenesis and larval production were unaffected while recruitment efficiency collapsed at low and variable pH, contributing to coral abundance decline and suggesting that life stages between larval release and early polyp growth are hindered by acidification. Exploring these processes is crucial to assess coral fate in the forthcoming acidified oceans, to preserve coral ecosystems and the socioeconomic services they provide.

Continue reading ‘Low and variable pH decreases recruitment efficiency in populations of a temperate coral naturally present at a CO2 vent’


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Ocean acidification in the IPCC AR5 WG II

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