An increase in global temperature combined with a shortage of nutrients and an increased level of carbon dioxide that lead to acidification pose a danger to marine organisms with calcium-containing shells. These organisms include corals, various marine molluscs, shrimps, echinoderms and some types of plankton.

What is ocean and sea acidification?

Acidification  of the ocean refers to a decrease in the pH value of the ocean over a long period of time, primarily caused by the intake of carbon dioxide (CO2) from the atmosphere.

As the level of carbon dioxide in the atmosphere increases, the oceans absorb part of this gas, acting as a buffer, where it reacts with water, giving carbonic acid, which dissociates, giving hydronium ions and ions of the acid residue.

The oceans and seas have the capacity to mitigate climate change by absorbing some of the carbon dioxide, but they are changing as well. This increases the acidity of sea water. However, the increase in acidity acts additionally by weakening the outer skeleton (exoskeleton) of marine organisms, i.e. their shells, which are usually made of calcium, because calcium reacts with carbonic acid anions.

In other words, seawater with increased acidity has a corrosive effect on marine organisms. Also, the chemical composition of shells can vary and in some cases marine organisms build shells with a higher percentage of magnesium, and it is precisely these shells that are particularly sensitive to a decrease in the pH value of the environment.

Acidification can disrupt the balance in marine ecosystems, particularly by stressing organisms that are sensitive to changes in pH. This can cause disruptions in food chains and affect populations of fish and other marine organisms.

Ocean acidification can lead to changes in the distribution and diversity of marine species. Some species may be favored by these changes, while others may be threatened or even become extinct. This can disrupt the entire marine ecosystem and cause negative consequences for the fishing industry and the overall biodiversity of the oceans and seas.

According to NOAA data , in the 200-plus years since the beginning of the industrial revolution, the concentration of carbon dioxide in the atmosphere has increased due to human activity, and during that time the pH of surface ocean waters has dropped by 0.1 pH unit. This may not sound like much, but the pH scale is logarithmic, so this change represents an increase in acidity of approximately 30 percent.

Acidification of the oceans and seas is called the “twin sister of climate change“. This is a direct consequence of the increase in the concentration of carbon dioxide in the atmosphere, just like climate change-

Data suggesting that acidification is literally melting marine organisms

In order to test the effects of ocean acidification in combination with other environmental factors, at Davis University in California and University of California Berkeley, David Swezey and his colleagues cultivated a species of bryozoa ( Bryozoa ) with the scientific name Jellyella tuberculata . This marine invertebrate builds colonies in the form of tiny honeycombs in warm subtropical waters around the world, most often on various floating objects or the shells of other marine invertebrates.

In a paper from 2017 entitled “Interactive effects of temperature, food and skeletal mineralogy mediate biological responses to ocean acidification in a widely distributed bryozoan” , published in the journal Proceedings of the Royal Society B at the end of April this year, the physiological stress of this species is described when the colonies were exposed to different concentrations of carbon dioxide in the water and to different temperatures and lack of nutrients.

Low temperatures and elevated carbon dioxide concentration caused stress in these organisms. Organisms that were in warmer water in combination with a limited amount of nutrients and an elevated concentration of carbon dioxide formed an external skeleton with a higher proportion of magnesium, and such a skeleton dissolved faster in an acidic environment.

The conditions described in the experiment already exist in the waters of California, because in the spring and summer the cooler waters of the Pacific, rich in carbon dioxide, come to the surface due to natural water circulation processes.

However, all marine organisms, not only the species studied in this paper, are very sensitive to sea and ocean acidification. The weakening of the shell due to the increase in the acidity of the environment will lead to a decrease in the abundance of all organisms with a calcified external skeleton, and as these organisms are often at the bottom of the food pyramid, the decrease in their number will be reflected in all those species that feed on these organisms.