Dissolving coral reefs: As oceans grow more acidic, marine life suffers

If you drive, fertilize your lawn, or buy sushi, you could be contributing to the demise of coral reefs.

Scientists call coral reefs the rainforests of the ocean, because these vibrant habitats support so much and such diverse life. But worldwide, coral reefs face serious threats.

Paulo Maurin, education coordinator for the National Oceanic and Atmospheric Administration’s coral reef conservation program, names three main threats to coral — land based pollution, adverse impacts of fishing, and climate change, which causes ocean acidification and coral bleaching. We all contribute to each one of these in some way, no matter where we live.

Land-based pollution includes the big things, such as agricultural and industrial run-off, but also little things like oil washing off your driveway. Many fish species used to produce our fish sticks and cat food (and even stock our home aquariums) are being removed from the ocean at unsustainable rates. The right type and number of fish are critical to maintaining healthy coral reefs; some fish eat algae, for example, and without enough of them doing so, too much algae grows over coral, eventually smothering it. Vehicle exhaust and emissions from the power plants producing our electricity increase the amount of carbon dioxide in the atmosphere, which causes ocean acidification.

Ocean acidification is the chemical change that occurs as the ocean absorbs carbon dioxide, or CO2. Water, or H2O, and CO2 combine with bicarbonate ions present in seawater to create carbonic acid, H2CO3. As more CO2 is emitted into the atmosphere, more of it ends up in seawater. Maurin says our oceans currently absorb approximately 2.3 gigatons of carbon per year, or about 48 percent of the anthropogenic (human-caused) carbon.

First, two major misconceptions many people have about ocean acidification (those who have even heard of it, that is). On one hand, some think the ocean is turning into battery acid. Others think the change is insignificant.

If you remember some high school chemistry, pH is a measure of the number of hydrogen, or H+, ions in a solution, with a low pH meaning a high H+ concentration (obviously a system designed to confuse mere mortals). The pH scale goes from 0 to 11, with acids on the lower half and bases on the upper, and 7 representing a neutral pH. Battery acid falls between 0 and 1, Maurin explains, lemon juice a little above 1, milk around 7. Human blood is about 8, as is seawater, and lye and ammonia near 11.

Recent measurements show that the ocean’s pH has changed from about 8.3 to 8.1.

That may not sound like much, but because the scale is logarithmic, as is the earthquake Richter scale, a 0.1 change in pH represents a factor of ten change. A 0.1 pH change means there are 30 percent more hydrogen ions in the water, or the water has become roughly 30 percent more acidic. The seas aren’t actually going to turn into acid, of course, but the change still has a huge effect.

As a result of acidification, calcium carbonate ions are chemically changed into a form different from that normally absorbed by shell-building organisms. This affects organisms that use calcium carbonate to make shells — including zooplankton, clams, mussels, crabs, oysters, and corals.

Loss of these animals will have an enormous ripple effect throughout ocean ecosystems. Oyster hatcheries in Washington and Oregon have already seen near total loss of spring spawn of oyster larvae (babies) in 2009 and 2010. Eventually, acidification may actually begin to dissolve the shells of mature animals as well.

NOAA scientists have been studying how CO2 affects the oceans for decades, and first noticed a drop in pH in the Pacific. Research ships around the world were then asked to test the pH in areas where they were working, and the combined results revealed the 0.1 drop. This is the biggest change to our oceans in the past 20 million years, Maurin points out, and it is happening so quickly that organisms can’t adapt to it the way they have adjusted to a constant variety of changes through the millennia.

“Ocean acidification is a very complex phenomena that affects marine organisms in complex ways,” Maurin says. “Not even all shelled organisms will be affected in the same way, or to the same degree.”
But we can count on them being affected. Extension of the Great Barrier Reef in Australia has already declined because calcification of coral there is down 14 percent. Ocean acidification will also affect plankton, which form the base of the marine food web — a food web that, ultimately, includes us.


Melissa Gaskill, culturemap, 18 January 2012. Article.

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