Can you imagine a world without seashells and corals? The ocean is packed with an organism known as calcifiers that rely on carbonate and calcium ions in seawater to construct their shells and exoskeletons. These organisms are being put in grave danger as the oceans continue to acidify because it impedes the development of calcification by reducing the number of carbonate and calcium ions to start with. As a result, the more acidified the water becomes, the greater energy the calcifiers will require to complete the calcification process.
The oceans have always served as the planet’s largest carbon sink, but the advent of the Industrial Revolution, especially over the last four decades, has given more carbon dioxide (CO2) than they can safely absorb. And in return, the ocean acidifies. Ocean acidification happens when CO2 is being absorbed at an increasing rate. The absorbed CO2 molecules react with water molecules to form carbonic acid. This compound then breaks up into a hydrogen ion and bicarbonate. The release of these excess hydrogen ions is what causes the pH of the ocean to decrease. This is detrimental for calcifiers as they eat away the building block that the organism depends on – carbonate ions.
An experiment was conducted by Jason Hall-Spencer, a professor of marine biology at the University of Plymouth, and marine biologist, Maria Cristina Buia, near the vents around the Castello Aragonese island. The vents produced a pH gradient, with a decreasing pH nearer to the vents. Hall-Spencer and his team recorded the pH levels around the island, organized a census of the living organisms, and tallied the total number of organisms in each of the different pH zones. However, when the team set up their quadrants closer to the vents, the number of organisms in those zones drastically decreased. Calcifiers were particularly hard-hit in the regions with low pH (pH 7.8); they made up three-quarters of the missing species. These included species like the prevalent barnacle Balanus perforatus, the mussel Mytilus galloprovincialis, and many others. As Hall-Spencer recalled: “Unfortunately, the biggest tipping point, the one at which the ecosystem starts to crash, is mean pH 7.8”
Although the experiment was only conducted on the island, it acted as a simulation of our ocean’s future if the current trend continues. Corals make up most of the marine calcifiers, which build reefs of calcium carbonate that act as some of the greatest hotspots of biodiversity in the ocean. Thousands of marine species rely on them for food or protection, and if all the corals die, many organisms would be in dire straits, and many more would face extinction.
But before all the calcifiers disappear, we, humans, could still take many actions. As the emissions of fossil fuel combustion contribute to more than 75% of the CO2 in our atmosphere, we should focus on finding ways that could help replace fossil fuels with more renewable or sustainable sources. It would certainly be a shame to see all the calcifiers disappear in our world!
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