Ocean acidification is a global phenomenon that results from the increasing uptake of carbon dioxide (CO2) from the atmosphere by the oceans.
As CO2 dissolves in seawater, it forms carbonic acid, which lowers the pH and reduces the availability of carbonate ions, the building blocks of many marine organisms.
Ocean acidification affects not only corals and shellfish but also microscopic plankton and benthic foraminifera, which are vital components of marine food webs and biogeochemical cycles.
How ocean acidification affects benthic foraminifera
(Photo : Joe Raedle/Getty Images)
Benthic foraminifera are single-celled organisms that produce chambered shells of calcium carbonate. They live in or on the seafloor, where they feed on organic matter and other microorganisms, as per Phys.org.
They are also important indicators of past and present environmental conditions, as their shells record information on temperature, salinity, oxygen levels, and pH.
A recent study by researchers at the Institute of Oceanology in the Chinese Academy of Sciences investigated how ocean acidification affects benthic foraminifera living on the continental shelf of the West Pacific Ocean.
They conducted experiments for eight months on foraminifera cultures taken from four sites in the Yellow Sea, involving 4,626 specimens attributed to 39 species.
They tested foraminifera response to marine conditions when progressively more carbon dioxide (400ppm, 800ppm, 1200ppm, and 1600ppm) was fed into the system.
This reflects modeling scenarios reported by the Intergovernmental Panel on Climate Change (IPCC) where worst-case scenario simulations are based on carbon dioxide concentrations of 1,600 ppm and above.
From the experiments, the scientists found that there was an overall decrease in benthic foraminifera abundance in response to increasing acidity, while shell diameter and thickness (and therefore weight) also reduced as there was less calcium carbonate in the ambient environment from which to build their shells.
This reduction in weight and size (dwarfism) is attributed to the foraminifera attempting to preserve the energetic costs of obtaining calcium carbonate from an ever-smaller reserve in the surrounding water.
The researchers also observed changes in the internal structure of the foraminifera shells, such as a reduced number of chambers, irregular chamber arrangement, abnormal shape and size, and increased porosity.
These changes indicate that ocean acidification impairs the biomineralization process and compromises the shell integrity and function of the foraminifera.
Moreover, the researchers found that different species of benthic foraminifera showed different sensitivities to ocean acidification.
Some species were more tolerant and resilient than others, suggesting that ocean acidification could alter the community composition and diversity of benthic foraminifera.
Implications for marine ecosystems and the global carbon cycle
The findings of this study have important implications for marine ecosystems and the global carbon cycle, as per Frontiers.
Benthic foraminifera plays a key role in transferring organic carbon from the surface to the deep ocean through their feeding activities and shell production.
They also contribute to the formation of carbonate sediments that buffer ocean acidity. By affecting their abundance, size, weight, structure, and diversity, ocean acidification could reduce their carbon sequestration capacity and weaken their buffering effect on ocean pH.
Furthermore, benthic foraminifera are a major food source for many marine animals, such as fish, crustaceans, echinoderms, and worms.
By reducing their availability and nutritional quality, ocean acidification could affect the trophic interactions and energy transfer in benthic food webs.
The researchers warn that ocean acidification is not the only threat facing benthic foraminifera.
Other stressors such as warming, deoxygenation, eutrophication, pollution, and habitat loss could also affect their survival and function.
Therefore, they call for more research on the combined effects of multiple stressors on benthic foraminifera and their ecological consequences.
Related article: Ocean Acidification Don't Affect the Behavior of Coral Reef Fishes
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