Posts Tagged 'calcification'

Impact of ocean acidification and warming on the diversity and the functioning of macroalgal communities (full thesis in French)

Predicted ocean acidification and warming for the end of the century may have drastic consequences on the structure and functioning of marine ecosystems. However, a lack of knowledge persists on the impact of future changes on the response of marine communities. This thesis aims to provide new understanding of the impact of ocean acidification and warming at the community level. For this, two ecosystems have been considered: rockpools, characterized by high physico-chemical variations, and maerl beds, with smaller variations. In the laboratory, artificial assemblages were created from the main calcareous and fleshy macroalgal and grazer species present in these two ecosystems. Created assemblages have been subjected to ambient and future temperature and pCO2 conditions. Ocean acidification and warming altered the structure and functioning of maerl bed assemblages, through an increase in the productivity of non-calcareous macroalgae and a decline in maërl calcification rates. The physiology of grazers is negatively impacted by future changes, which altered assemblages’ trophic structure. On the other hand, ocean acidification and warming had no effect on the productivity of rockpool assemblages. The highly variable environment may thus increase the resistance of rockpool communities to future changes, compared to communities from more stable environments, such as maerl beds.

Continue reading ‘Impact of ocean acidification and warming on the diversity and the functioning of macroalgal communities (full thesis in French)’

Nitrogen enrichment offsets direct negative effects of ocean acidification on a reef-building crustose coralline alga

Ocean acidification (OA) and nutrient enrichment threaten the persistence of near shore ecosystems, yet little is known about their combined effects on marine organisms. Here, we show that a threefold increase in nitrogen concentrations, simulating enrichment due to coastal eutrophication or consumer excretions, offset the direct negative effects of near-future OA on calcification and photophysiology of the reef-building crustose coralline alga, Porolithon onkodes. Projected near-future pCO2 levels (approx. 850 µatm) decreased calcification by 30% relative to ambient conditions. Conversely, nitrogen enrichment (nitrate + nitrite and ammonium) increased calcification by 90–130% in ambient and high pCO2 treatments, respectively. pCO2 and nitrogen enrichment interactively affected instantaneous photophysiology, with highest relative electron transport rates under high pCO2 and high nitrogen. Nitrogen enrichment alone increased concentrations of the photosynthetic pigments chlorophyll a, phycocyanin and phycoerythrin by approximately 80–450%, regardless of pCO2. These results demonstrate that nutrient enrichment can mediate direct organismal responses to OA. In natural systems, however, such direct benefits may be counteracted by simultaneous increases in negative indirect effects, such as heightened competition. Experiments exploring the effects of multiple stressors are increasingly becoming important for improving our ability to understand the ramifications of local and global change stressors in near shore ecosystems.

Continue reading ‘Nitrogen enrichment offsets direct negative effects of ocean acidification on a reef-building crustose coralline alga’

Effects of ocean acidification on algae growth and feeding rates of juvenile sea urchins

Highlights

• Ocean acidification increase the feeding rates of juveniles of P. lividus on algae reared at low pH.
• However the effects of ocean acidification on feeding rates of D. africanum were not differences between algae reared under low pH and control pH.
• This investigation highlights indirect effects of ocean acidification such as increase in herbivores pressure as consequence of change in algae palatability.
• Ocean acidification affects growth of 9 algae species from Canary Islands.
• A future scenario of climate change could affect the palatability of algae and their growth.

Abstract

The recent decrease in seawater pH has stimulated a great deal of research on the effects of ocean acidification on various organisms. Most of these studies have mainly focused on the direct effects of acidification on organisms. However, the effects on ecological interactions have been poorly studied. In this paper we have focused on determining the effects of acidification on feeding rates of two species of sea urchins, Paracentrotus lividus and Diadema africanum through laboratory experiments. Nine algae species were reared under two pH treatmens (ph = 8.1 vs. pH = 7.6) for 10 days. We evaluated possible changes in calcification rates, growth and internal structure. Then these algae were offered to juvenile sea urchins for 7 days, evaluating the consumption rates of juvenile sea urchins under these different pH conditions. The algae reared in the control treatment showed higher growth rates and concentration of calcium carbonate, however no internal structural changes were observed in any algae. Juvenile Paracentrotus lividus showed higher consumption rates on algae previously subjected to pH 7.6 than on algae reared under control conditions and between algae species in low pH.The algae most consumed were C. liebetruthii, C. abies-marina and C. elongata by P. lividus juveniles from low pH treatment. However in D. africanum the feeding rates were similar between treatments. This study demonstrated the negative effects of low pH on various species of algae in growth, and indirectly the increase in herbivory rates of juvenile sea urchins on algae reared under low pH.

Continue reading ‘Effects of ocean acidification on algae growth and feeding rates of juvenile sea urchins’

Quantitative interpretation of vertical profiles of calcium and pH in the coral coelenteron

Highlights

• In this study, pH and Ca2+ microsensors were reported together with a theoretical analysis by a reaction-diffusion model to study the dynamics of pH and Ca2+ in the coelenteron of the reef corals Turbinaria reniformis and Acropora millepora.
• Our study showed that Ca2+ concentrations linearly decreased from the mouth to the base of the coelenteron due to calcification.
• The estimated H+ gradient between the coelenteron cavity and the calcification site was >10 times higher than previously predicted between outside seawater and the calcification site.
• Our numerical simulation reveals that OA reduces the internal pH at the base of the coelenteron, and this pH decline is greatly amplified in corals with a deeper coelenteron.

Abstract

Scleratinian corals (hard corals) and their symbiotic algae are the ecological engineers of biodiverse and geological important coral reef habitats. The complex, linked physiological processes that enable the holobiont (coral + algae) to calcify and generate reef structures are consequently of great interest. However, the mechanism of calcification is difficult to study for several reasons including the small spatial scales of the processes and the close coupling between the symbiont and host. In this study, we explore the utility of pH and Ca2+ microelectrodes for constraining the rates and spatial distribution of photosynthesis, respiration, and calcification. The work focuses on vertical profiles of pH and Ca2+ through the coelenteron cavity, a semi-isolated compartment of modified seawater amenable to quantitative interpretation. In two studied species, Turbinaria reniformis and Acropora millepora, Ca2+ concentrations decreased in a roughly linear manner from the mouth to the base of the coelenteron, indicating the primary physiological process affecting Ca2+ concentration is removal for calcification below the coelenteron. In contrast, the H+ concentration remained relatively constant over much of the coelenteron cavity before it increased sharply toward the base of the coelenteron, indicative of proton-pumping from the calcification fluid below. The estimated H+ gradient between the coelenteron cavity and the calcification site was >10 times higher than previously predicted. Consequently, the energy required to export protons from the calcifying fluid was estimated to be ~3 times higher than previously calculated. A one-dimensional reaction-diffusion model was used to interpret the pH profile considering the effects of photosynthesis, respiration, and calcification. This model provided a good fit to the observed pH profile and helped to constrain the rates and spatial distribution of these processes. Our modeling results also suggested that adult corals with deeper polyps may be more sensitive to ocean acidification (OA) because of enhanced difficulty to transport H+ out of the coelenteron and into the surrounding seawater.

Continue reading ‘Quantitative interpretation of vertical profiles of calcium and pH in the coral coelenteron’

High pCO2 levels affect metabolic rate, but not feeding behavior and fitness, of farmed giant mussel Choromytilus chorus

Benthic habitats such as intertidal areas, sandy or rocky shores, upwelling zones, and estuaries are characterized by variable environmental conditions. This high variability of environmental stressors such as temperature, salinity, and pH/ pCO2 levels have been shown to impose restrictions on organismal performance. The giant mussel Choromytilus chorus forms intertidal and subtidal mussel beds in estuarine zones associated with fjords occurring in southern Chile and is an important aquacultural resource in Patagonia. In this study, we estimated the sensitivity of physiological traits and energy balance of C. chorus juveniles exposed to 3 pCO2 treatments (500, 750, and 1200 µatm) for 30 d. Results showed that in acidified, high pCO2 conditions, C. chorus juveniles had increased metabolic rates; however, other physiological traits (clearance and ingestion rates, ammonia excretion, absorption efficiency, growth rate, biomass production, net calcification, and dissolution rates) were not affected. These results suggest that when subjected to acidification, the adaptive response of C. chorus triggers tradeoffs among physiological traits that favor sustained feeding and growth in order to combat increased metabolic stress. As has been reported for other marine organisms, chronic exposure to variable pH/ pCO2 in their native habitats, such as estuarine zones, could explain the differential acclimatization capacity of giant mussels to cope with the increase in pCO2. Additionally, the fact that the mussels did not suffer from mortality indicates that increased pCO2 levels may have chronic, but not lethal, effects on this species under these experimental conditions.

Continue reading ‘High pCO2 levels affect metabolic rate, but not feeding behavior and fitness, of farmed giant mussel Choromytilus chorus’

Increased food supply mitigates ocean acidification effects on calcification but exacerbates effects on growth

Because many of the negative effects of ocean acidification on marine life may result from underlying energetic short-falls associated with increased metabolic demands, several studies have hypothesized that negative responses to high CO2 could be reduced by energy input. Although this hypothesis was supported by a recent meta-analysis, we believe that the meta-analytic calculation used was not appropriate to test the stated hypothesis. Here, we first clarify the hypothesis put forward, the crux being that the effects of increased food supply and CO2 interact statistically. We then test this hypothesis by examining the available data in a more appropriate analytical framework. Using factorial meta-analysis, we confirm that food addition has a positive effect and CO2 has a negative effect on both growth and calcification. For calcification, food addition did indeed reduce CO2 impacts. Surprisingly, however, we found that food addition actually exacerbated the effects of acidification on growth, perhaps due to increased scope upon which CO2 effects can act in food-replete situations. These interactive effects were undetectable using a multilevel meta-analytic approach. Ongoing changes in food supply and carbonate chemistry, coupled with under-described, poorly understood, and potentially surprising interactive outcomes for these two variables, suggest that the role of food should remain a priority in ocean acidification research.

Continue reading ‘Increased food supply mitigates ocean acidification effects on calcification but exacerbates effects on growth’

Reply to ‘Increased food supply mitigates ocean acidification effects on calcification but exacerbates effects on growth’

In the Brown et al. study ‘Increased food supply mitigates ocean acidification effects on calcification but exacerbates effects on growth’ they show disagreement with the tested hypothesis and data analysis methodology used in our 2016 study. We acknowledge careful criticism and a constructive dialogue are necessary to progress science and address these issues in this reply.

Continue reading ‘Reply to ‘Increased food supply mitigates ocean acidification effects on calcification but exacerbates effects on growth’’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book