Seaweed species can curb acidification of oceans, shows study

Scientists led by the Indian Council of Agricultural Research- Central Marine Fisheries Institute (ICAR-CMFRI) have identified a species of green algae that can reduce the acidification of seawater induced by climate change. According to the study, published in the latest edition of the Journal of Marine Biological Association of India, green seaweed Chaetomorpha antennina was able to prevent the corrosive effects of acidic seawater on molluscs and sea urchins.

Acidification of seawater occurs when atmospheric carbon dioxide (CO2) released via anthropogenic (manmade) activities, leads to a gradual decrease in pH levels in seawater. On a scale of 0 to 14, a pH level below seven turns water acidic, while more than seven makes water alkaline.

The ICAR-CMFRI study showed that like terrestrial vegetation, Chaetomorpha antennina uses CO2 for photosynthesis, removing dissolved CO2. To identify the effect of dissolved carbon dioxide – which leads seawater to turn into carbonic acid – the three-member team studied the dissolution rate of the outer shells of dead molluscs and spines of sea urchin when treated with seawater. For this, they used seawater with different dissolved CO2 levels (0, 100, 200, 250 and 300ppm), both, in the presence and absence of the seaweed. Results showed that the weight of shells reduced as the concentration of dissolved CO2 increased, indicating that carbonate materials dissolved from the skeletal structures. However, the weight loss of the samples was curbed in when seaweed was introduced.

“This biological efficiency of green seaweed Chaetomorpha antennina can be attributed to sequestration of CO2 during photosynthesis and subsequent release of dissolved organic carbon,” stated the study.

“The role played by the seaweed in the net reduction in the weight of shells and spines was higher in lower CO2 levels, which suggests the need to optimise the quantity of live seaweed biomass to fight higher levels of dissolved CO2,” P Kaladharan, principal investigator, ICAR-CMFRI. “This trend warrants the need for more seaweed beds along the coast or extensive seaweed farms to combat ocean acidification.”

Increasing acidity in the oceans is one of the consequences of climate change. According to the International Union for Conservation of Nature (IUCN), rise in ocean temperatures and oxygen loss act concurrently with seawater acidification. Together, they have the potential to alter marine ecosystems and impact coastal protection and the fishing industry.

Data released by the Smithsonian Ocean in May estimated that oceans at present absorb 22 million tonnes of CO2 daily. While the average pH on the ocean surface prior to the beginning of the industrial era (late 18th century) was around 8.2, today it is about 8.1. A 2008 study showed that a pH drop of 0.1 translates roughly to a 30% increase in acidity.

Snehal Fernandes, Hindustan Times, 21 October 2019. Article.

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Ocean acidification in the IPCC AR5 WG II

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