The Certain Phenomenon of Ocean Acidification and its Uncertain Ramifications

A quarter of the carbon dioxide emissions from human systems enters the ocean. There is no scientific doubt that intakes of carbon dioxide from the atmosphere have caused a pH increase in the acidity of the Earth’s oceans. On March 6th, Scott Doney, a chemist from the Woods Hole Oceanographic Institution, discussed his research on how acidification will affect what our oceans will look like in the future.

Possible biological impacts of the huge influx of carbon dioxide include reduced shell formation of corals, mollusks, plankton, and crustaceans. But studies of coral show that some species are very sensitive to acidification, while others are not. As the oceans continue to acidify, not all sea life is going to die, but rather we are going to see shifts in the composition of ecological communities. Population shifts may decrease the ocean’s total biodiversity, and they may impact coastal economies: “the species we’re used to catching in particular places aren’t going to be there.”

Studies also indicate that increased carbon dioxide levels may affect fish behavior. One experiment compared clown fish behavior in channels with differing scents: one with predator scent, one with a normal scent. In un-acidified waters, the clown fish immediately fled the predator scent. With elevated carbon dioxide, the fish spent much more time in the predator channel, their scenting systems impaired. Another study demonstrated that acidified waters negatively affected fish cognition.

In addition to acidification, oceans are being polluted by excess nitrogen from agricultural inputs, which run off fields into streams, and ultimately enter the oceans. Excess nitrogen in coastal ecosystems cause phytoplankton to burgeon into large blooms. When the phytoplankton dies and decomposes, bacteria deplete the local system of oxygen, and release more carbon dioxide, creating environments untenable for fish. These local environments are called dead zones. The effects of eutrophication and acidification are synergistic, meaning the sum of the two problems is worse than each on its own.

Fishing and tourism industries face increasing economic insecurity. Mollusks and crustaceans make up half of US catch in terms of economic value. Vibrant coral reefs ecosystems bring a large percentage of the GDP to tourist-centric countries. “The rates at which changes are happening are going to accelerate over the next century,” said Doney.

 

Written by Claire Lafave ’12, CES Research Assistant