Posts Tagged 'laboratory'

Exposure to elevated pCO2 does not exacerbate reproductive suppression of Aurelia aurita jellyfish polyps in low oxygen environments

Eutrophication-induced hypoxia is one of the primary anthropogenic threats to coastal ecosystems. Under hypoxic conditions, a deficit of O2 and a surplus of CO2 will concurrently decrease pH, yet studies of hypoxia have seldom considered the potential interactions with elevated pCO2 (reduced pH). Previous studies on gelatinous organisms concluded that they are fairly robust to low oxygen and reduced pH conditions individually, yet the combination of stressors has only been examined for ephyrae. The goals of this study were to determine the individual and interactive effects of hypoxia and elevated pCO2 on the asexual reproduction and aerobic respiration rates of polyps of the scyphozoan Aurelia aurita during a manipulative experiment that ran for 36 d. pCO2 and pO2 were varied on a diel basis to closely mimic the diel conditions observed in the field. Exposure to low dissolved oxygen (DO) reduced asexual budding of polyps by ~50% relative to control conditions. Under hypoxic conditions, rates of respiration were elevated during an initial acclimation period (until Day 8), but respiration rates did not differ between DO levels under prolonged exposure. There was no significant effect of increased pCO2 on either asexual reproduction or aerobic respiration, suggesting that elevated pCO2 (reduced pH) did not exacerbate the negative reproductive effects of hypoxia on A. aurita polyps.

Continue reading ‘Exposure to elevated pCO2 does not exacerbate reproductive suppression of Aurelia aurita jellyfish polyps in low oxygen environments’

Calcification in a marginal sea – influence of seawater [Ca2+] and carbonate chemistry on bivalve shell formation

In estuarine coastal systems such as the Baltic Sea, mussels suffer from low salinity which limits their distribution. Anthropogenic climate change is expected to cause further desalination which will lead to local extinctions of mussels in the low saline areas. It is commonly accepted that mussel distribution is limited by osmotic stress. However, along the salinity gradient environmental conditions for biomineralization are successively becoming more adverse as a result of reduced [Ca2+] and dissolved inorganic carbon (CT) availability. In larvae, calcification is an essential process starting during early development with formation of the prodissoconch I (PD I) shell which is completed under optimal conditions within 2 days.

Experimental manipulations of seawater [Ca2+] start to impair PD I formation in Mytilus larvae at concentrations below 3 mM, which corresponds to conditions present in the Baltic at salinities below 8 g kg-1. In addition, lowering dissolved inorganic carbon to critical concentrations (< 1 mM) similarly affected PD I size which was well correlated with calculated ΩAragonite and [Ca2+][HCO3]/[H+] in all treatments. Comparing results for larvae from the western Baltic with a population from the central Baltic revealed significantly higher tolerance of PD I formation to lowered [Ca2+] and [Ca2+][HCO3]/[H+] in the low saline adapted population. This may result from genetic adaptation to the more adverse environmental conditions prevailing in the low saline areas of the Baltic.

The combined effects of lowered [Ca2+] and adverse carbonate chemistry represent major limiting factors for bivalve calcification and can thereby contribute to distribution limits of mussels in the Baltic Sea.

Continue reading ‘Calcification in a marginal sea – influence of seawater [Ca2+] and carbonate chemistry on bivalve shell formation’

Impacts of near-future ocean acidification and warming on the shell mechanical and geochemical properties of gastropods from intertidal to subtidal zones

Many marine organisms produce calcareous shells as the key structure for defence, but the functionality of shells may be compromised by ocean acidification and warming. Nevertheless, calcifying organisms may adaptively modify their shell properties in response to these impacts. Here, we examined how reduced pH and elevated temperature affect shell mechanical and geochemical properties of common grazing gastropods from intertidal to subtidal zones. Given the greater environmental fluctuations in the intertidal zone, we hypothesized that intertidal gastropods would exhibit more plastic responses in shell properties than subtidal gastropods. Overall, three out of five subtidal gastropods produced softer shells at elevated temperature, while intertidal gastropods maintained their shell hardness at both elevated pCO2 (i.e. reduced pH) and temperature. Regardless of pH and temperature, degree of crystallization was maintained (except one subtidal gastropod) and carbonate polymorph remained unchanged in all tested species. One intertidal gastropod produced less soluble shells (e.g. higher calcite/aragonite) in response to reduced pH. In contrast, subtidal gastropods only produced aragonite which has higher solubility than calcite. Overall, subtidal gastropods are expected to be more susceptible than intertidal gastropods to shell dissolution and physical damage under future seawater conditions. The increased vulnerability to shell dissolution and predation could have serious repercussions for their survival and ecological contributions in the future subtidal environment.

Continue reading ‘Impacts of near-future ocean acidification and warming on the shell mechanical and geochemical properties of gastropods from intertidal to subtidal zones’

Comment on “The complex effects of ocean acidification on the prominent N2-fixing cyanobacterium Trichodesmium”

Hong et al. (Reports, 5 May 2017, p. 527) suggested that previous studies of the biogeochemically significant marine cyanobacterium Trichodesmium showing increased growth and nitrogen fixation at projected future high CO2 levels suffered from ammonia or copper toxicity. They reported that these rates instead decrease at high CO2 when contamination is alleviated. We present and discuss results of multiple published studies refuting this toxicity hypothesis.

Continue reading ‘Comment on “The complex effects of ocean acidification on the prominent N2-fixing cyanobacterium Trichodesmium”’

Combined effects of ocean acidification with morphology, water flow, and algal acclimation on metabolic rates of tropical coralline algae

Coral reefs are currently facing multiple stressors that threaten their health and function, including ocean acidification (OA). OA has been shown to negatively affect many reef calcifiers, such as coralline algae that provide many critical contributions to reef systems. Past studies have focused on how OA independently influences coralline algae, but more research is necessary as it is expected that the effects of OA on coralline algae will vary depending on many other factors. To better understand how algal morphology, water flow, and algal acclimation interact with OA to affect coralline algae, three studies were conducted in Moorea, French Polynesia, from June 2015 to July 2016. In January 2016, I tested the hypothesis that algal individuals with higher morphological complexity would exhibit faster metabolic rates under ambient pCO2 conditions, but would also demonstrate higher sensitivity to OA conditions. For three species of crustose coralline algae, Lithophyllum kotschyanum, Neogoniolithon frutescens, and Hydrolithon reinboldii, algal individuals with more complex morphologies demonstrated faster rates of calcification, photosynthesis, and respiration in the ambient pCO2 treatment than individuals with simpler morphological forms. There also appeared to be a relationship between morphology and sensitivity to OA conditions, with calcification rates negatively correlated with higher morphological complexity. In the summers of 2015 and 2016, I conducted three experiments examining the effects of water flow and OA on different morphologies of coralline algae to test the hypotheses that increased flow would enhance metabolic rates and mitigate the effects of OA, and that algae with more complex morphologies would be more responsive to increased water flow and more sensitive to OA conditions. A field experiment investigating the effects of water flow on Amphiroa fragilissima, L. kotschyanum, N. frutescens, and H. reinboldii detected enhanced rates of calcification, photosynthesis, and respiration with increased flow, and this relationship appeared to be the strongest for the crustose algal species with the highest structural complexity. A flume manipulation examining the combined effects of water flow and OA on A. fragilissima, L. kotschyanum, N. frutescens, H. reinboldii, and Porolithon onkodes suggested that coralline algal species with high structural complexity were the most sensitive to OA conditions. Finally, A. fragilissima and L. kotschyanum were maintained in different pCO2 and water flow conditions in a long-term mesocosm experiment, which indicated that flow was unable to mitigate the effects of OA on coralline algae. In the summer of 2016, I investigated the acclimation potential of A. fragilissima and L. kotschyanum to OA, and predicted that the original treatment conditions would induce phenotypic modifications that would influence algal responses to the end treatment. There were negative effects of long-term exposure of coralline algae to elevated pCO2 conditions on calcification and photosynthesis, though partial acclimation in calcification to OA was observed. The instantaneous exposure of elevated pCO2 had negative impacts on algal calcification, but had a nominal effect on photosynthesis. No effects of long-term or instantaneous exposure to elevated pCO2 were observed for respiration. The results of these studies indicate that the coralline algal response to OA conditions will likely be complex and depend on numerous factors including water flow, morphology, and acclimation potential. Therefore, it is critical that future studies further investigate the effects of these factors; specifically examining the mechanisms that underlie these responses in order to better predict the future of coralline algae and thus coral reef ecosystems in a more acidic ocean.

Continue reading ‘Combined effects of ocean acidification with morphology, water flow, and algal acclimation on metabolic rates of tropical coralline algae’

Advancing ocean acidification biology using Durafet® pH electrodes

Research assessing the biological impacts of global ocean change often requires a burdensome characterization of seawater carbonate chemistry. For laboratory-based ocean acidification research, this impedes the scope of experimental design. Honeywell Durafet® III pH electrodes provide precise and continuous seawater pH measurements. In addition to use in oceanographic sensor packages, Durafets can also be used in the laboratory to track and control seawater treatments via Honeywell Universal Dual Analyzers (UDAs). Here we provide performance data, instructions, and step-by-step recommendations for use of multiple UDA-Durafets. Durafet pH measurements were within ±0.005 units pHT of spectrophotometric measurements and agreement among eight Durafets was better than ±0.005 units pHT. These results indicate equal performance to Durafets in oceanographic sensor packages, but methods for calibration and quality control differ. Use of UDA-Durafets vastly improves time-course documentation of experimental conditions and reduces person-hours dedicated to this activity. Due to the versatility of integrating Durafets in laboratory seawater systems, this technology opens the door to advance the scale of questions that the ocean acidification research community aims to address.

Continue reading ‘Advancing ocean acidification biology using Durafet® pH electrodes’

Variability in larval gut pH regulation defines sensitivity to ocean acidification in six species of the Ambulacraria superphylum

The unusual rate and extent of environmental changes due to human activities may exceed the capacity of marine organisms to deal with this phenomenon. The identification of physiological systems that set the tolerance limits and their potential for phenotypic buffering in the most vulnerable ontogenetic stages become increasingly important to make large-scale projections. Here, we demonstrate that the differential sensitivity of non-calcifying Ambulacraria (echinoderms and hemichordates) larvae towards simulated ocean acidification is dictated by the physiology of their digestive systems. Gastric pH regulation upon experimental ocean acidification was compared in six species of the superphylum Ambulacraria. We observed a strong correlation between sensitivity to ocean acidification and the ability to regulate gut pH. Surprisingly, species with tightly regulated gastric pH were more sensitive to ocean acidification. This study provides evidence that strict maintenance of highly alkaline conditions in the larval gut of Ambulacraria early life stages may dictate their sensitivity to decreases in seawater pH. These findings highlight the importance of identifying and understanding pH regulatory systems in marine larval stages that may contribute to substantial energetic challenges under near-future ocean acidification scenarios.

Continue reading ‘Variability in larval gut pH regulation defines sensitivity to ocean acidification in six species of the Ambulacraria superphylum’


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