Ocean acidification
Definition of Ocean acidification:
The process whereby atmospheric carbon dioxide dissolves in seawater producing carbonic acid, which subsequently lowers pH of surrounding seawater; widely thought to be happening on a global scale.
This is the common definition for Ocean acidification, other definitions can be discussed in the article
|
Note
Other processes also contribute to acidification, especially in eutrophic coastal waters: decomposition of organic material, nitrification in surface water (promoted by sewage discharge) and oxidation processes in sediments[1].
Influence of ocean acidification on a few bivalve species
The following is extracted from (Mele et al., 2023[2]):
Climate change and ocean acidification, induced by rising atmospheric carbon dioxide (CO2), are global phenomena which threaten marine organisms biomineralizing calcium carbonate (CaCO3) shells. The average acidity of ocean surface waters is expected to decrease by 0.14–0.43 units (i.e., a decrease in pH from about 8.1 to about 7.7 - 7.95) with a simultaneous increase of +2 oC and +4 oC in sea surface temperature by 2100. Consequently, the seawater bicarbonate (HCO-3) and carbonic acid (H2CO3) equilibrium is affected causing under-saturation of oceanic calcite and aragonite worldwide.
As the ocean’s pH decreases, the extent of the effect of ocean acidification is dependent on the shell structure and composition of the organism. Calcium carbonate can present most commonly as one of two polymorphs, calcite being the stable hexagonal form, and aragonite being considered metastable and more vulnerable to ocean acidification.
Both the mussel Mytilus species (spp.) and the oyster Magallana gigas form calcite layers, but Mytilus spp. also forms aragonite on the inner shell layer. Although the two polymorphs share the same chemical formula, the different atomic arrangement of aragonite increases susceptibility to ocean acidification, compared to calcite. Mytilus spp. and Magallana gigas together account for 46% of global mollusc production within the aquaculture industry. Previous research has shown that increasing food supply to molluscs during ocean acidification experiments can limit shell corrosion and increase shell growth.
When seawater temperature rises, Mytilus spp. appear to rely on metabolically sourced carbon for shell calcite potentially from extrapallial fluid (fluid from outside the mantle) rather than from mantle tissue or from the feed under ocean acidification. The altered biomineralization pathway in Mytilus spp. into the shell calcite layer, is sufficient to maintain the growth of the shell, as well as its thickness and hardness. On the other hand, Mytilus spp. increases environmentally sourced carbon for aragonite under low pH conditions. This response is sufficient to maintain and increase shell thickness in high water temperature scenarios. Low pH also affects M. gigas from a feeding and nutrient perspective shown by variation in mantle nitrogen isotopes, but biomineralization pathway is maintained along with growth. Thus, the response to ocean acidification and extra feeding results appear species-specific according to the carbon sourcing preference of Mytilus spp. and M. gigas. In a natural scenario, plankton blooms would be more beneficial to M. gigas, as in this study shows overall better shell performance and resilience than Mytilus spp.
A study of Vlaminck et al. (2022[3]) on the physiological response of the white furrow shell Abra alba to three pH treatments (pH = 8.2, pH = 7.9 and pH = 7.7) showed no pH effect on survival. However, lowered respiration and calcification rates, decreased energy intake (lower absorption rate) and increased metabolic losses (increased excretion rates) occurred at pH ∼ 7.7. These physiological responses resulted in a negative Scope for Growth and a decreased condition index at this pH. This suggests that the physiological changes may not be sufficient to sustain survival in the long term, which would undoubtedly translate into consequences for ecosystem functioning.
See also
Review on the impacts of ocean stratification by Kroeker et al. (2014[4]).
An extensive article on ocean acidification can be found in the Wikipedia: Ocean acidification.
References
- ↑ Wallace, R.B. and Gobler, C.J. 2021. The role of algal blooms and community respiration in controlling the temporal and spatial dynamics of hypoxia and acidification in eutrophic estuaries. Marine Pollution Bulletin 172, 12908
- ↑ Mele, I., McGill, R.A.R., Thompson, J., Fennell, J. and Fitzer, S. 2023. Ocean acidification, warming and feeding impacts on biomineralization pathways and shell material properties of Magallana gigas and Mytilus spp. Marine Environmental Research 186, 105925
- ↑ Vlaminck, E., Moens, T., Vanaverbeke, J. and Van Colen, C. 2022. Physiological response to seawater pH of the bivalve Abra alba, a benthic ecosystem engineer, is modulated by low pH. Marine Environmental Research 179, 105704
- ↑ Kroeker, K.J., Kordas, R.L., Crim, R., Hendriks, I.E., Ramajos, L., Singh, G,S, Duartes, C.M. and Gattusa, J-P. 2014. Impacts of ocean acidification on marine organisms: quantifying sensitivities and interaction with warming. Global Change Biology 19: 1884–1896, doi: 10.1111/gcb.12179. https://onlinelibrary.wiley.com/doi/epdf/10.1111/gcb.12179
