Phytoplankton are the microscopic organisms found in abundance in the world’s oceans. They form the basis of the food chain, and are thus crucial to marine life. They also play a central role in the global carbon cycle, helping to remove carbon dioxide from the atmosphere. However, scientists have found that the numbers of certain crustacean species, like Emiliania huxleyi, one of the commonest forms of phytoplankton, seem to be decreasing in the Southern Ocean surrounding Antarctica.
Researchers at the University of Colorado at Boulder believe this is due to the growing acidification of the world’s oceans, caused by global climate change. In an article published in Geophysical Research Letters, they wrote: “These results suggest that large-scale shifts in the ocean carbon cycle are already occurring and highlight organism and marine ecosystem vulnerability in a changing climate.”
E. Huxleyi or EHUX is a coccolithophore, a type of “calcifying” plankton that uses sunlight to build its microscopic shell of calcium carbonate. It is the source of more than half the calcium carbonate present in the oceans. Satellite data show a 24 per cent decline in the amount of calcium carbonate in the Southern Ocean over the past 17 years. This is attributed to a decline in numbers of EHUX as well as the observation that the shells are thinner. The CU – Boulder study used statistical analysis and data collected by the SEAWifs and MODIS satellites.
E. Huxleyi are microscopic organisms that “bloom” periodically, turning the water milky white. These blooms, typically occurring in early summer, are so extensive that they can be seen from space. E. Huxleyi are the third commonest species of phytoplankton with a global distribution, from tropical to arctic waters.
Ocean acidification occurs when carbon dioxide is dissolved in the water. Scientists at the National Atmospheric and Oceanic Administration estimate that the world’s oceans have become 30 per cent more acidic since the Industrial Revolution in the early nineteenth century. Environmental groups estimate that in 2013, the world’s oceans absorbed 3 billion tonnes of carbon produced by human sources.