Posts Tagged 'biological response'

Molecular adaptation of molluscan biomineralisation to high-CO2 oceans – the known and the unknown

Highlights

• Shell proteins and ion transporters are two important machineries involved in molluscan biomineralisation.

• Energy budgeting plays a key role in adaptation to OA.

• Omega myth theory and proton flux limitation theory on ocean acidification.

• Understanding epigenetic changes in response to environmental stressors is required.

• There is only limited understanding of molluscan carbon uptake mechanisms.

Abstract

High-CO2 induced ocean acidification (OA) reduces the calcium carbonate (CaCO3) saturation level (Ω) and the pH of oceans. Consequently, OA is causing a serious threat to several ecologically and economically important biomineralising molluscs. Biomineralisation is a highly controlled biochemical process by which molluscs deposit their calcareous structures. In this process, shell matrix proteins aid the nucleation, growth and assemblage of the CaCO3 crystals in the shell. These molluscan shell proteins (MSPs) are, ultimately, responsible for determination of the diverse shell microstructures and mechanical strength. Recent studies have attempted to integrate gene and protein expression data of MSPs with shell structure and mechanical properties. These advances made in understanding the molecular mechanism of biomineralisation suggest that molluscs either succumb or adapt to OA stress. In this review, we discuss the fate of biomineralisation process in future high-CO2 oceans and its ultimate impact on the mineralised shell’s structure and mechanical properties from the perspectives of limited substrate availability theory, proton flux limitation model and the omega myth theory.

Furthermore, studying the interplay of energy availability and differential gene expression is an essential first step towards understanding adaptation of molluscan biomineralisation to OA, because if there is a need to change gene expression under stressors, any living system would require more energy than usual. To conclude, we have listed, four important future research directions for molecular adaptation of molluscan biomineralisation in high-CO2 oceans: 1) Including an energy budgeting factor while understanding differential gene expression of MSPs and ion transporters under OA. 2) Unraveling the genetic or epigenetic changes related to biomineralisation under stressors to help solving a bigger picture about future evolution of molluscs, and 3) Understanding Post Translational Modifications of MSPs with and without stressors. 4) Understanding carbon uptake mechanisms across taxa with and without OA to clarify the OA theories on Ω.

Continue reading ‘Molecular adaptation of molluscan biomineralisation to high-CO2 oceans – the known and the unknown’

Impacts of Zn and Cu enrichment under ocean acidification scenario on a phytoplankton community from tropical upwelling system

Highlights

• Phytoplankton showed higher resilience to increasing CO2.

• Few centric diatoms showed positive response to increasing CO2 supply.

• Addition of Zn under increasing CO2 inhibited cell division, but not biomass.

• The combined effects of increasing CO2 and Cu addition was insignificant on growth.

• Cu addition at high CO2 level promoted toxigenic pennate diatom growth.

Abstract

Increasing dissolution of CO2 in the surface ocean is rapidly decreasing its pH and changing carbon chemistry which is further affecting marine biota in several ways. Phytoplankton response studies under the combination of elevated CO2 and trace metals are rare. We have conducted two consecutive onboard incubation experiments (R. V. Sindhu Sadhana; August 2017) in the eastern Arabian Sea (SW coast of India) during an upwelling event. A nutrient enriched diatom bloom was initiated onboard and grown under ambient (≈400 μatm, A-CO2) and high CO2 levels (≈1000 μatm; H–CO2) with different zinc (Zn; 1 nM) and copper (Cu) concentrations (1 nM, 2 nM and 8 nM). Phytoplankton community composition and the dominant genera were different during these two experiments. CO2 enrichment alone did not show any significant growth stimulating impact on the experimental community except enhanced cell density in the first experiment. Addition of Zn at A-CO2 level revealed no noticeable responses; whereas, the same treatment under H–CO2 level significantly reduced cell number. Considerably high protein content under H–CO2+Zn treatment was possibly counteracting Zn toxicity which also caused slower growth rate. Cu addition did not show any noticeable impact on growth and biomass production except increased protein content as well as decreased carbohydrate: protein ratio. This can be attributed to relatively higher protein synthesis than carbohydrate to alleviate oxidative stress generated by Cu. The centric diatom Chaetoceros and toxin producing pennate diatom Pseudo-nitzschias howed no significant response to either CO2 or Zn enrichment. Large centric diatom Leptocylindrus and Skeletonema responded positively to Zn addition in both CO2 levels. The former species showed the most sensitive response at the highest Cu and H–CO2 treatment; whereas, the pennate diatoms Nitzschia and Pseudo-nitzschia (toxigenic diatom) showed higher resilience under elevated CO2 and Cu levels. This observation indicated that in future ocean, increasing CO2 concentrations and trace metal pollution may potentially alter phytoplankton community structure and may facilitate toxigenic diatom bloom in the coastal waters.

Continue reading ‘Impacts of Zn and Cu enrichment under ocean acidification scenario on a phytoplankton community from tropical upwelling system’

A review of transgenerational effects of ocean acidification on marine bivalves and their implications for sclerochronology

Highlights

1. Effects of moderately elevated pCO2 on marine bivalves are potentially alleviated following transgenerational exposure.

2. Transgenerational effects on geochemical properties of marine bivalve shells can have widespread implications for sclerochronology.

Abstract

Ocean acidification can negatively impact marine bivalves, especially their shell mineralization processes. Consequently, whether marine bivalves can rapidly acclimate and eventually adapt in an acidifying ocean is now increasingly receiving considerable attention. Projecting the fate of this vulnerable taxonomic group is also pivotal for the science of sclerochronology – the study which seeks to deduce records of past environmental changes and organismal life-history traits from various geochemical properties of periodically layered hard tissues (bivalve shells, corals, fish otoliths, etc.). In this review, we provide a concise overview of the long-term and transgenerational responses of marine bivalves to elevated pCO2 manifested at different levels of biological organization, with a specific focus on responses of geochemical properties (stable carbon and oxygen isotopes, minor and trace elements and microstructures) of their shells. Without exception, positive transgenerational responses to an elevated pCO2 scenario projected for the year 2100 have been found in all five bivalve species hitherto studied, under the umbrella of two non-genetic mechanisms (increased maternal provisioning and epigenetic inheritance), suggesting that marine bivalves have remarkable transgenerational phenotypic plasticity which allows them to respond plastically and acclimate rapidly in an acidifying ocean. Rapid transgenerational acclimation, especially in terms of physiological processes, however, hinders a reliable interpretation of proxy records. Transgenerationally acclimated bivalves can actively modify the calcification physiology in response to elevated pCO2, which in turn affects the processes of almost all geochemical proxies preserved in their shells. In particular, stable carbon isotopes, metabolically regulated elements (Na, K, Cu, Zn, Fe, etc.), and shell microstructures can be highly biased. In this context, we propose a number of challenges and opportunities the field of sclerochronology may face.

Continue reading ‘A review of transgenerational effects of ocean acidification on marine bivalves and their implications for sclerochronology’

Combined effects of ocean acidification and hypoxia on the early development of the thick shell mussel Mytilus coruscus

Ocean acidification has become serious, and seawater hypoxia has become evident in acidified waters. The combination of such stressors may have interactive effects on the fitness of marine organisms. In order to investigate the interactive effects of seawater acidification and hypoxia on the early development of marine bivalves, the eggs and sperm of the thick shell mussel Mytilus coruscus were exposed to combined treatments of pH (8.1, 7.7, 7.3) and dissolved oxygen (2, 6 mg/L) for 96 h culture observation to investigate the interactive effects of seawater acidification and hypoxia on the early development of marine bivalves. Results showed that acidification and hypoxia had significant negative effects on various parameters of the early development of the thick shell mussel. However, hypoxia had no effect on fertilization rate. Significant interactions between acidification and hypoxia were observed during the experiment. Short-term exposure negatively influenced the early development of the thick shell mussel but did not affect its survival. The effects of long-term exposure to these two environmental stresses need further study.

Continue reading ‘Combined effects of ocean acidification and hypoxia on the early development of the thick shell mussel Mytilus coruscus’

Linking energy budget to physiological adaptation: how a calcifying gastropod adjusts or succumbs to ocean acidification and warming

Highlights

• Energetics and shell properties of gastropods were measured under future climate.

• Ocean warming increased the feeding rate and hence energy budget of gastropods.

• The boosted energy budget was linked to increased shell growth and shell strength.

• Ocean acidification caused these positive effects of warming to become negative.

• Energy budget determined the adjustability of shell building process in calcifiers.

Abstract

Accelerating CO2 emissions have driven physico-chemical changes in the world’s oceans, such as ocean acidification and warming. How marine organisms adjust or succumb to such environmental changes may be determined by their ability to balance energy intake against expenditure (i.e. energy budget) as energy supports physiological functions, including those with adaptive value. Here, we examined whether energy budget is a driver of physiological adaptability of marine calcifiers to the near-future ocean acidification and warming; i.e. how physiological energetics (respiration rate, feeding rate, energy assimilation and energy budget) relates to adjustments in shell growth and shell properties of a calcifying gastropod (Austrocochlea concamerata). We found that ocean warming boosted the energy budget of gastropods due to increased feeding rate, resulting in faster shell growth and greater shell strength (i.e. more mechanically resilient). When combined with ocean acidification, however, the gastropods had a substantial decrease in energy budget due to reduced feeding rate and energy assimilation, leading to the reduction in shell growth and shell strength. By linking energy budget to the adjustability of shell building, we revealed that energy availability is critical to determine the physiological adaptability of marine calcifiers to the changing oceanic climate.

Continue reading ‘Linking energy budget to physiological adaptation: how a calcifying gastropod adjusts or succumbs to ocean acidification and warming’

Contrasting changes in diel variations of net community calcification support that carbonate dissolution can be more sensitive to ocean acidification than coral calcification

Previous studies have found that calcification in coral reefs is generally stronger during the day, whereas dissolution is prevalent at night. On the basis of these contrasting patterns, the diel variations of net community calcification (NCC) were monitored to examine the relative sensitivity of CaCO3 production (calcification) and dissolution in coral reefs to ocean acidification (OA), using two mesocosms that replicated a typical subtropical coral reef ecosystem in southern Taiwan. The results revealed that the daytime NCC remained unchanged, whereas the nighttime NCC decreased between the control (ambient) and treatment (OA) conditions, suggesting that carbonate dissolution could be more sensitive to OA than coral calcification. The average sensitivity of the integrated daily NCC to changes in the seawater saturation state (Ωa) was estimated to be a reduction of 54% in NCC per unit change in Ωa, which is consistent with the global average. In summary, our results support the prevailing anticipation that OA would lead to a reduction in the overall accretion of coral reef ecosystems. However, increased CaCO3 dissolution rather than decreased coral calcification could be the dominant driving force responsible for this OA-induced reduction in NCC.

Continue reading ‘Contrasting changes in diel variations of net community calcification support that carbonate dissolution can be more sensitive to ocean acidification than coral calcification’

Effects of inorganic carbon concentration and pH on carbonic anhydrase activity of gametophytes of Saccharina japonica

Carbonic anhydrase (CA) was considered to be an important component of carbon concentrating mechanism (CCM) of algae. It was an inducible enzyme. Environmental factors, especially dissolved inorganic carbon and pH, were known to affect CA activity. Effects of inorganic carbon (CO2 and ) and pH on CA activity of gametophytes of Saccharina japonica were evaluated in this study. Under high-CO2 condition (3% CO2), the activity of external CA (CAext) was significantly decreased (P < 0.05) from 33.92 REA/g FW to 27.69 REA/g FW. In contrast, the internal CA (CAint) and total CA activities were elevated significantly (p < 0.01) from 36.83 REA/g FW to 48.80 REA/g FW, and from 70.75 REA/g FW to 76.49 REA/g FW, respectively. Addition of an appropriate concentration of to the medium, CAint and total CA activities were promoted significantly, although the activity of CAext was inhibited significantly (P < 0.05). In higher concentration (up to 1680 mg/L), the activity of CAint was promoted to 60.81REA/g FW, which was twice that of the control. Higher activities of CAint and total CA were induced at low pH. At pH 6.0, the highest activities of CAint (110.85 REA/g FW) and total CA (128.17 REA/g FW) were induced. However, at pH 9.0, the activities of CAint and total CA were reduced to the lowest of 23.31REA/g FW and 42.19 REA/g FW, respectively. This is the first report about the successful detection of CAext activity of gametophytes of S. japonica. The results would provide data for the analysis of Ci acquisition and transport mechanism in S.japonica gametophytes.

Continue reading ‘Effects of inorganic carbon concentration and pH on carbonic anhydrase activity of gametophytes of Saccharina japonica’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book