Posts Tagged 'mortality'



Legacy of multiple stressors: responses of gastropod larvae and juveniles to ocean acidification and nutrition

Ocean acidification poses a significant threat to calcifying invertebrates by negatively influencing shell deposition and growth. An organism’s performance under ocean acidification is not determined by the susceptibility of one single life-history stage, nor is it solely controlled by the direct physical consequences of ocean acidification. Shell development by one life-history stage is sometimes a function of the pH or pCO2 levels experienced during earlier developmental stages. Furthermore, environmental factors such as access to nutrition can buffer organismal responses of calcifying invertebrates to ocean acidification, or they can function as a co-occurring stressor when access is low. We reared larvae and juveniles of the planktotrophic marine gastropod Crepidula fornicata through combined treatments of nutritional stress and low pH, and we monitored how multiple stressors endured during the larval stage affected juvenile performance. Shell growth responded non-linearly to decreasing pH, significantly declining between pH 7.6 and pH 7.5 in larvae and juveniles. Larval rearing at pH 7.5 reduced juvenile growth as a carryover effect. Larval rearing at pH 7.6 reduced subsequent juvenile growth despite the absence of a negative impact on larval growth, demonstrating a latent effect. Low larval pH magnified the impact of larval nutritional stress on competence for metamorphosis and increased carryover effects of larval nutrition on juvenile growth. Trans-life-cycle effects of larval nutrition were thus modulated by larval exposure to ocean acidification.

Continue reading ‘Legacy of multiple stressors: responses of gastropod larvae and juveniles to ocean acidification and nutrition’

Temporal effects of ocean warming and acidification on coral–algal competition

While there is an ever-expanding list of impacts on coral reefs as a result of ocean warming and acidification, there is little information on how these global changes influence coral–algal competition. The present study assessed the impact of business-as-usual ocean warming and acidification conditions on the survivorship, calcification, photosynthesis and respiration of the coral–algal interaction between the macroalga Halimeda heteromorpha and the coral Acropora intermedia over 8 weeks in two seasons. The physiological responses of A. intermedia and H. heteromorpha were highly dependent on season, with both organisms demonstrating optimal rates of calcification and photosynthesis under present-day conditions in summer. Contact with H. heteromorpha did not influence A. intermedia survivorship, however did reduce long-term calcification rates. Photosynthetic rates of A. intermedia were influenced by algal contact temporally in opposing directions, with rates reduced in winter and increased in summer. Enhanced photosynthetic rates as a result of algal contact were not enough to offset the combined effects of ocean warming and acidification, which regardless of coral–algal contact, reduced survivorship, calcification and photosynthesis of A. intermedia and the calcification rates of H. heteromorpha. These findings provide experimental support for the idea that the effects of coral–algal competition are temporally variable, and help improve our understanding of how future ocean warming and acidification may alter the dynamics of coral–algal interactions.

Continue reading ‘Temporal effects of ocean warming and acidification on coral–algal competition’

No compromise between metabolism and behavior of decorator crabs in reduced pH conditions

Many marine calcifiers experience metabolic costs when exposed to experimental ocean acidification conditions, potentially limiting the energy available to support regulatory processes and behaviors. Decorator crabs expend energy on decoration camouflage and may face acute trade-offs under environmental stress. We hypothesized that under reduced pH conditions, decorator crabs will be energy limited and allocate energy towards growth and calcification at the expense of decoration behavior. Decorator crabs, Pelia tumida, were exposed to ambient (8.01) and reduced (7.74) pH conditions for five weeks. Half of the animals in each treatment were given sponge to decorate with. Animals were analyzed for changes in body mass, exoskeleton mineral content (Ca and Mg), organic content (a proxy for metabolism), and decoration behavior (sponge mass and percent cover). Overall, decorator crabs showed no signs of energy limitation under reduced pH conditions. Exoskeleton mineral content, body mass, and organic content of crabs remained the same across pH and decoration treatments, with no effect of reduced pH on decoration behavior. Despite being a relatively inactive, osmoconforming species, Pelia tumida is able to maintain multiple regulatory processes and behavior when exposed to environmental pH stress, which underscores the complexity of responses within Crustacea to ocean acidification conditions.

Continue reading ‘No compromise between metabolism and behavior of decorator crabs in reduced pH conditions’

CO2 leakage simulation: effects of the decreasing pH to the survival and reproduction of two crustacean species

Highlights

• Both species show reduction in their fitness when exposed to CO2 acidification scenarios.

• The isopod Cyathura carinata survives at pH as low as 6.5, not the amphipod Elasmopus rapax

• The impairment observed in E. rapax was more severe than in C. carinata.

• Regardless the lengths of the lifespan, both species were unable to produce offspring.

Abstract

The effects of CO2-related acidification on two crustacean populations, the isopod Cyathura carinata and the amphipod Elasmopus rapax, were studied. Three pH levels were tested: artificial seawater without CO2 injection and two levels of reduced pH. Even though RNA:DNA ratio was reduced for both species, no statistical significant differences were found between the control and the treatments. Both species experienced a reduction in survivorship, longevity and the body length of surviving animals; although the impairment observed in E. rapax was more severe than in C. carinata. The long life span isopod and the short life span amphipod experienced a high degree of impairment in the reproduction, likely due to the reallocation of resources from reproduction to body maintenance and increasing survival by postponing the brood production. Regardless of the underlying processes and the energetic pathways, both experienced failure to reproduce, which could lead to the local extinction of these species.

Continue reading ‘CO2 leakage simulation: effects of the decreasing pH to the survival and reproduction of two crustacean species’

Cuttlefish early development and behaviour under future high CO2 conditions

Atmospheric CO 2 levels are rising since the beginning of the Industrial Era, and concomitantly, the uptake of CO 2 by the oceans is increasing and changing the seawater chemistry, a phenomenon known as ocean acidification (OA). These changes can compromise key biological traits of many marine organisms, with potential cascading effects to population and ecosystem levels. Besides the significant neurological/physiological impairments, there is increasing evidence of detrimental OA effects on the behavioural ecology of certain marine taxa, including in cephalopods. Yet, the previous behavioural studies performed in these highly developed invertebrates were only focused on squids and the potential impacts in cuttlefish behaviour are still unknown. Within this context, the main objectives of this dissertation were to investigate OA effects in the development and behaviour of the common cuttlefish ( Sepia officinalis ) early-life stages – from early embryogenesis until 20 days after hatching, namely by exposing them to either present day ( ~ 400 μatm) and to the near-future levels of p CO 2 ( ~ 1000 μatm; ΔpH = 0.4). A comprehensive assessment of OA effects on cuttlefish development was performed by gauging embryogenesis duration, hatching success, early survival rate and body size measures (e.g. weight and length). Furthermore, different aspects of the cuttlefish behavioural ecology, including shelter-seeking, hunting behaviour and response to a visual alarm cue, were analysed to achieve a holistic overview of the OA impacts in cuttlefish early development. The present work did not find any evidence that OA future conditions compromise the cuttlefish embryonic development. The development time, hatching success, survival rate, and the length and weight of newly-hatched cuttlefish were similar between normocapnia and hypercapnia treatments. The Fulton’s Index was the only parameter that showed significant differences, with higher values to the hypercapnia treatment, which may be related with a denser cuttlebone. Concerning to the behaviours analysed, and in contrast with previous cephalopod studies, the results suggest a certain behavioural resilience of the cuttlefish hatchlings towards near-future acidification conditions. The behaviours of hunting, shelter-seeking and response to a visual alarm cue did not show significant differences between treatments. Their nekton-benthic (and active) lifestyle, their adaptability to the abiotic-fluctuating coastal environment and to the adverse conditions inside their eggs may favour the odds of the common cuttlefish recruits to endure the future acidified ocean. Nonetheless, this species is not only exposed to acidification in their natural environment, they may be also particularly susceptible to other anthropogenic pressure and other climate change-related variables. The cumulative effects of multiple stressors should be further addressed to accurately predict what the future reserves to this ecologically and economically important species.

Continue reading ‘Cuttlefish early development and behaviour under future high CO2 conditions’

Tipping points of gastric pH regulation and energetics in the sea urchin larva exposed to CO2 induced seawater acidification

Highlights

• We determined the sensitivity thresholds for survival development and growth in sea urchin larvae exposed to acidified conditions.

• Determination of physiological parameters including midgut pH homeostasis, metabolic rates and expression of midgut acid-base transporters demonstrates a physiological tipping point at pH 7.2.

• This work demonstrates substantial resilience of an important environmental engineer to the ongoing phenomenon of ocean acidification.

Abstract

Sea urchin larvae reduce developmental rates accompanied by changes in their energy budget when exposed to acidified conditions. The necessity to maintain highly alkaline conditions in their digestive systems led to the hypothesis that gastric pH homeostasis is a key trait affecting larval energy budgets leading to distinct tipping points for growth and survival.

To test this hypothesis, sea urchin larvae were reared for 10 days in different pH conditions ranging from pH 7.0 to pH 8.2. Survival, development and growth rates were determined demonstrating severe impacts < pH 7.2. To test the effects of pH on midgut alkalization we measured midgut pH and monitored the expression of acid-base transporters. While larvae were able to maintain their midgut pH at 8.9–9.1 up to an acidification level of pH 7.2, midgut pH was decreased in the lower pH treatments. The maintenance of midgut pH under low pH conditions was accompanied by dynamic changes in the expression level of midgut acid-base transporters. Metabolic rates of the larvae increased with decreasing pH and reached a threshold between pH 7.0 and pH 7.3 where metabolic rates decreased again. Methylation analyses on promoter CpG islands were performed for midgut acid-base transporter genes to test for possible epigenetic modifications after 10-day exposure to different pH conditions. This analysis demonstrated no correlation between methylation level and pH treatments suggesting low potential for epigenetic modification of acid-base transporters upon short-term exposure. Since a clear tipping point was identified at pH 7.2, which is much lower than near-future OA scenarios, this study suggests that the early development of the purple sea urchin larva has a comparatively high tolerance to seawater acidification with substantial acclimation capacity and plasticity in a key physiological trait under near-future OA conditions.

Continue reading ‘Tipping points of gastric pH regulation and energetics in the sea urchin larva exposed to CO2 induced seawater acidification’

Ocean acidification causes mortality in the medusa stage of the cubozoan Carybdea xaymacana

Ocean pH is decreasing due to anthropogenic activities, and the consequences of this acidification on marine fauna and ecosystems are the subject of an increasing number of studies. Yet, the impact of ocean acidification (OA) on several abundant and ecologically important taxa, such as medusozoans, is poorly documented. To date there have been no studies on the effect of post-2050 OA projections on the medusa stage of jellyfish. As medusae represent the reproductive stage of cnidarians, negative impacts on adult jellyfish could severely impact the long-term survival of this group. Using a laboratory experiment, we investigated the effect of 2300 OA projections (i.e. pH of 7.5) on the mortality rate of the medusa-stage of the cubozoan species Carybdea xaymacana, compared to ambient seawater pH conditions (i.e. pH of 8.1). After a 12-h exposure to OA, Cxaymacana medusae suffered higher mortality rates compared to ambient conditions. This study represents the first evidence of the potential lethal effects of post-2050 OA projections on jellyfish. The higher metabolic rates of cubozoans compared to other cnidarians might make box jellyfish more vulnerable to OA. A decrease in the density of cnidarians could lead to harmful ecological events, such as algal blooms.

Continue reading ‘Ocean acidification causes mortality in the medusa stage of the cubozoan Carybdea xaymacana’


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Ocean acidification in the IPCC AR5 WG II

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