January 16 – Seed Pearls Of Change

Today’s factismal: The oysters in Chesapeake Bay once filtered all the water in the bay in four days; today it takes them a year.

Oysters are amazing animals. They filter feed by sucking in dirty water, passing it over their gills, and then noshing on the sediment and floating debris that gets trapped in their mucus. As they do so, they clarify the water and make it suitable for other critters to live in. At one time, there were so many oysters in Chesapeake Bay (located by Baltimore) that they could clean all of the water in the bay in just four days. Unfortunately, over the past century, the number of oysters in the bay have decreased due to over harvesting (people like to eat oysters as much as oysters like to eat crud), pollution, and changes in the water chemistry.

An oyster shares its tank with a horseshoe crab (My camera)

An oyster shares its tank with a horseshoe crab
(My camera)

How can a change in water chemistry affect an oyster? By making it harder to grow a shell. Oysters create shells (and pearls) out of calcium carbonate (CaCO3) that is dissolved in the water as calcium ions (Ca++) and carbonate ions (CO3–). But when carbon dioxide (CO2) dissolves in water it forms carbonic acid (H2CO3) which dissolves calcium carbonate; as a result, the shells of the oysters are thinner, more brittle, and take more energy to build. (This is also the cause behind coral bleaching.) And that leads to what is known in the oyster business as “lazy larva syndrome”. The young oysters have to spend so much energy building their shells that they have little left for eating or swimming. At the end of a year, oysters that grow up in a more acidic ocean are smaller and don’t reproduce well.

Bleached coral (My camera)

Bleached coral
(My camera)

The interesting thing is that it takes only a small change in ocean chemistry to create a big change in the number of lazy larvae. Thus far, the oceans have changed from a pH of 8.25 to 8.14; almost all of that change is due to increases in atmospheric CO2.  And the other interesting thing about this is that it isn’t just oysters that are affected; the change in ocean pH has led to more coral bleaching and slower growth of bony fish like tuna. So what is a citizen scientist to do?

Other than making sure your tires are inflated properly, perhaps the most powerful thing you can do is help the folks at Ventus as they map out all of the sources of CO2 in the world starting with the power plants. They hope that by producing an hour by hour map of how much CO2 is produced, we can identify easy places to cut back on CO2 without cutting back on our standard of living. If you’d like to help (or just see what they’ve found so far), then blow on over to:
http://ventus.project.asu.edu/

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