Posts Tagged 'calcification'

Diurnally fluctuating pCO2 modifies the physiological responses of coral recruits under ocean acidification

Diurnal pCO2 fluctuations have the potential to modulate the biological impact of ocean acidification (OA) on reef calcifiers, yet little is known about the physiological and biochemical responses of scleractinian corals to fluctuating carbonate chemistry under OA. Here, we exposed newly settled Pocillopora damicornis for 7 days to ambient pCO2, steady and elevated pCO2 (stable OA) and diurnally fluctuating pCO2 under future OA scenario (fluctuating OA). We measured the photo-physiology, growth (lateral growth, budding and calcification), oxidative stress and activities of carbonic anhydrase (CA), Ca-ATPase and Mg-ATPase. Results showed that while OA enhanced the photochemical performance of in hospite symbionts, it also increased catalase activity and lipid peroxidation. Furthermore, both OA treatments altered the activities of host and symbiont CA, suggesting functional changes in the uptake of dissolved inorganic carbon (DIC) for photosynthesis and calcification. Most importantly, only the fluctuating OA treatment resulted in a slight drop in calcification with concurrent up-regulation of Ca-ATPase and Mg-ATPase, implying increased energy expenditure on calcification. Consequently, asexual budding rates decreased by 50% under fluctuating OA. These results suggest that diel pCO2 oscillations could modify the physiological responses and potentially alter the energy budget of coral recruits under future OA, and that fluctuating OA is more energetically expensive for the maintenance of coral recruits than stable OA.

Continue reading ‘Diurnally fluctuating pCO2 modifies the physiological responses of coral recruits under ocean acidification’

Ecosystem calcification and production in two Great Barrier Reef coral reefs: methodological challenges and environmental drivers

This thesis investigates the drivers of coral reef ecosystem metabolism and the abilities of the different methodologies and analytical approaches to accurately represent reef dynamics. It encompassed tracing natural nutrient additions through bird guano into a coral cay. Developing a new, automated system for measuring carbonate chemistry for coral reef metabolism and the effects of mass coral bleaching on ecosystem functioning were quantified. Overall, it showed that natural nutrient additions and bleaching differentially affect coral reef metabolism and that subtle differences in analytical methods, sampling approaches, and data interpretation techniques can cause significant variation in metabolic estimates.

Continue reading ‘Ecosystem calcification and production in two Great Barrier Reef coral reefs: methodological challenges and environmental drivers’

An ocean acidification-simulated system and its application in coral physiological studies

Due to the elevated atmospheric carbon dioxide, ocean acidification (OA) has recently emerged as a research theme in marine biology due to an expected deleterious effect of altered seawater chemistry on calcification. A system simulating future OA scenario is crucial for OA-related studies. Here, we designed an OA-simulated system (OASys) with three solenoid-controlled CO2 gas channels. The OASys can adjust the pH of the seawater by bubbling CO2 gas into seawaters via feedback systems. The OASys is very simple in structure with an integrated design and is new-user friendly with the instruction. Moreover, the OASys can monitor and record real-time pH values and can maintain pH levels within 0.02 pH unit. In a 15-d experiment, the OASys was applied to simulate OA in which the expected target pH values were 8.00, 7.80 and 7.60 to study the calcifying response of Galaxea fascicularis. The results showed daily mean seawater pH values held at pH 8.00±0.01, 7.80±0.01 and 7.61±0.01 over 15 d. Correspondingly, the coral calcification of G. fascicularis gradually decreased with reduced pH.

Continue reading ‘An ocean acidification-simulated system and its application in coral physiological studies’

Gene expression profiles of two coral species with varied resistance to ocean acidification

Recent studies have indicated that various corals might have different degrees of resistance to elevated CO2 levels. However, the underlying molecular mechanism accounting for these differences is still poorly understood. In this study, RNA-seq data were analyzed to identify differentially expressed genes in two coral species (Acropora austera and Acropora cerealis) in response to high CO2 levels. The calcification rates were higher in high CO2 treatment than the control in A. austera, but was not significantly different in A. cerealis. A KEGG database search revealed that in both coral species, most Ca2+ transporters were present in the calcium signaling pathway, which could be important in the CO2 regulation of coral calcification. The gene expression levels of many CO2 and HCO3 transporters were not affected by elevated CO2. Nevertheless, high CO2 levels did have an effect on the expression of certain Ca2+ transporters. The upregulation of Ca2+ transporters likely explained the higher resistance of A. austera to high CO2 than A. cerealis.

Continue reading ‘Gene expression profiles of two coral species with varied resistance to ocean acidification’

Obligate ectosymbionts increase the physiological resilience of a scleractinian coral to high temperature and elevated pCO2

Invertebrate ectosymbionts within the coralla of scleractinians enhance host fitness through protection from corallivores and nutrient addition. Here, we explore the ectosymbiotic relationship between the coral Pocillopora verrucosa and the crab Trapezia serenei and the shrimp Alpheus spp., to test for effects on coral calcification under contrasts of seawater temperature (27.7 °C and 29.9 °C) and pH (ambient, 8.0 and reduced, 7.7). Regardless of temperature, ectosymbionts depressed calcification by 55% (vs without ectosymbionts) at ambient pH; however, ectosymbionts only depressed calcification under ambient pH but not at reduced pH. These results suggest that P. verrucosa grows fastest at ambient pH without ectosymbionts, but when ectosymbionts are present, colonies are protected from further declines in calcification at reduced pH. This implies that there may be a change from a currently parasitic ectosymbiont–coral relationship to a commensal relationship that could increase fitness advantages for corals hosting crustacean ectosymbionts under ocean acidification conditions.

Continue reading ‘Obligate ectosymbionts increase the physiological resilience of a scleractinian coral to high temperature and elevated pCO2’

Coral responses to ocean warming and acidification: implications for future distribution of coral reefs in the South China Sea

Highlights

• SST increased at rates of 0.038–0.074 °C/year in recent decade in the SCS.
• pH decreased faster than previous prediction in our study sites.
• Some reef corals were not able to survive at 33 °C in our culture experiments.
• Subtropical waters with temperature of <30 °C may serve as refugia for corals.

Abstract

The annual sea surface temperature increased at a rate of 0.038 to 0.074 °C/year in recent decade, and pH decreased at a rate of 0.012–0.014/year in two coastal waters of the South China Sea. Therefore, a culture experiment was conducted to study the effects of acidification and warming on coral calcification rates. The calcification of three coral species were significantly reduced during the exposure to elevated CO2, while other three coral species were not significantly affected. The reef coral Pocillopora damicornis was resistant to high CO2, but was not able to survive during the exposure to 33 °C in our culture experiments. Our findings suggested that some corals might not survive in tropical areas if coral could not adapt to warming rapidly, and subtropical coastal waters with temperature of <30 °C will serve as refugia for the corals resistant to high CO2 at the end of this century.

Continue reading ‘Coral responses to ocean warming and acidification: implications for future distribution of coral reefs in the South China Sea’

The potential environmental response to increasing ocean alkalinity for negative emissions

The negative emissions technology, artificial ocean alkalinization (AOA), aims to store atmospheric carbon dioxide (CO2) in the ocean by increasing total alkalinity (TA). Calcium carbonate saturation state (ΩCaCO3) and pH would also increase meaning that AOA could alleviate sensitive regions and ecosystems from ocean acidification. However, AOA could raise pH and ΩCaCO3 well above modern-day levels, and very little is known about the environmental and biological impact of this. After treating a red calcifying algae (Corallina spp.) to elevated TA seawater, carbonate production increased by 60% over a control. This has implication for carbon cycling in the past, but also constrains the environmental impact and efficiency of AOA. Carbonate production could reduce the efficiency of CO2 removal. Increasing TA, however, did not significantly influence Corallina spp. primary productivity, respiration, or photophysiology. These results show that AOA may not be intrinsically detrimental for Corallina spp. and that AOA has the potential to lessen the impacts of ocean acidification. However, the experiment tested a single species within a controlled environment to constrain a specific unknown, the rate change of calcification, and additional work is required to understand the impact of AOA on other organisms, whole ecosystems, and the global carbon cycle.

Continue reading ‘The potential environmental response to increasing ocean alkalinity for negative emissions’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book