Diatoms Under MicroscopeOcean acidification is having a dangerous effect on phytoplankton, the largest source of the planet’s oxygen and the cornerstone of the marine food chain.

Scientists aboard the RV Melville are studying the effects of carbon saturation on phytoplankton, also known as microalgae, along the western coast of the United States. The crew brings together researchers from the National Oceanographic and Atmospheric Administration (NOAA), the Pacific Marine Environmental Lab, as well as teams from universities in Maine, Hawaii and Canada.

The ocean absorbs about 50 percent of all the carbon dioxide on the planet. This is a natural part of the global ecosystem, but increased levels of CO2 in the atmosphere have led to an increased level of absorption. More CO2 changes the chemical composition of the ocean, causing the pH level to drop and raising the water’s acidity.

Scientists already know that ocean acidification reduces the mineral content of the water, making it harder for certain creatures to build their shells and rendering corals more vulnerable. What the scientists aboard the Melville are currently studying is how a lower pH level affects phytoplankton.

Floating near the surface of the water and absorbing the sun’s rays, phytoplankton produce approximately 60 percent of Earth’s oxygen. The Melville team is visiting “upwelled” zones off the coasts of Washington, Oregon and California, places where centuries-old carbon dioxide is pushed to the surface. In these spots, the ocean is more acidic, providing a glimpse at what ocean conditions may be like in the future if countries fail to reduce their carbon emissions.

The project’s lead investigator, Dr. Bill Cochlan, has outlined what the team expects to find: “Our hypothesis is that ocean acidification will affect the quantity and quality of certain metabolities within the phytoplankton, specifically lipids and essential fatty acids.”

That hypothesis has proved right so far. Their study shows that more acidic waters make it difficult for phytoplankton to absorb nutrients, rendering them vulnerable to disease and toxins. These toxins can then be passed on to the creatures that consume them.

Domoic acid is one such neurotoxin. Produced by a species of phytoplankton, domoic acid can accumulate in mussels and be passed on to humans. “Changes in the future ocean could stimulate the levels of domoic acid in the natural population,” says Professor Charles Trick, one of the Melville researchers.

Another toxin from the diatom Pseudo-nitschia can cause permanent short-term memory loss and even death. The diatom has been shown to produce more of this toxin when pH levels are low.

Add to this toxification the fact that weakened phytoplankton would produce less oxygen and you get not only a compromised ocean but also a weaker atmosphere as well. It’s a recipe for disaster made from the smallest ingredients possible.

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  1. […] affects to animals, plants and humans. UVB has been shown to inhibit the reproductive cycle of phytoplankton, which form the basis of the ocean’s food chain, as well as fish, shrimp, crabs and amphibians. […]

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