If you thought only lemons were acidic, you have yet to hear the story of the acidification of the sea! The shellfish are asking for survival courses, because with all this acidity their shells are getting a little too thin for their liking!
- What is meant by acidification?
- Impact on the marine ecosystem
- Acidification, mitigation and adaptation
What is meant by acidification?
The acidification of oceans and seas is a major environmental concern today, linked to carbon dioxide (CO₂) emissions into the atmosphere.
When CO₂ is absorbed by water, a chemical reaction takes place that leads to the formation of carbonic acid, thus lowering the pH of the water and making it more acidic.
This change in pH affects the life of many marine species, especially those with calcareous shells such as corals and molluscs, which find it increasingly difficult to form and maintain their protective structures.
The sea has absorbed around 20-30% of total anthropogenic CO₂ emissions since the 1980s, altering the chemical composition of the water.
According to the IPCC, compared to pre-industrial levels, the pH of the oceans has dropped by about 0.1 units, corresponding to an increase in acidity of about 26%. If we do not reduce CO₂ emissions, the pH could drop a further 0.3-0.4 units by the end of the century, an increase in acidity of up to 150% compared to pre-industrial levels.
Impact on the marine ecosystem
Ocean acidification has devastating effects on many marine life forms, especially on organisms with calcareous shells such as corals, molluscs and some types of plankton.
These organisms find it increasingly difficult to form and maintain their protective structures. In a nutshell, due to a PH that is too acidic, animals will not be able to create new calcareous shells, and those that are present will tend to melt.
This condition alters the structure of marine food chains, as key species such as corals, which serve as habitats for many fish and other marine creatures, are severely affected.
Impacts are significant on echinoderms such as starfish and sea urchins, but also on bivalves used in human nutrition such as oysters, clams and mussels.
Finally, the loss of carbonate shelves causes a lowering of the seabed around coral reefs. It reduces their protective function and increases the risk of coastal flooding.
This threatens fishing areas and human communities that depend on the sea for their livelihoods, jeopardising food security and the local economy, including tourism.
Acidification, mitigation and adaptation
The main mitigation strategies involve reducing greenhouse gas emissions by decreasing the amount of CO₂ that ends up in the oceans. Sustainable management of marine ecosystems, protecting coral reefs and marine protected areas, helps mitigate the effects of acidification.
The American The Ocean Foundation launched a specific initiative on the topic in 2016 and supports scientists, policy makers and communities to monitor and understand ocean acidification locally and globally. Coastal restoration projects have been funded and partnerships formed with governments and intergovernmental agencies.
Despite the most pessimistic predictions, some marine organisms seem to adapt to new conditions through unexpected evolutionary mechanisms. For example, corals containing aragonite seem to adapt better to more acidic conditions than those with calcite shells.
A study by the German Oceanic Centre GEOMAR showed that the algae Emiliania huxleyi can adapt to higher levels of carbonic acid. After 500 generations in the laboratory, these algae showed better growth and calcification than the original strains.
Results such as this also indicate the need to consider evolutionary processes in future studies to assess the biological consequences of global change.
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