The Effects of Ocean Acidification on Coral

A Comparison between the Alkalinity Anomaly and Buoyant Weight Methods of Measurement

Aaron CevallosAdvisor: Andreas Andersson, Ph.D.

Summer 2010

What is ocean acidification? What is causing it?

•The ocean absorbs approximately 1/3rd of the CO2 emitted to the atmosphere from the burning of fossil fuels. 

•As CO2 dissolves in seawater, the pH of the water decreases. Since the beginning of the industrial revolution, ocean pH has dropped globally by approximately 0.1 pH units.

•By the end of this century, we may expect to see changes in pH that are the greatest in 21 million years.

http://ioc3.unesco.org/oanet/FAQacidity.html

Evidence of ocean acidification at BATS

N. Bates

Bermuda coral reef: the canary in a coal mine?

Buddemeier et al. 2004, based on Veron 1995

Alex Venn

-Marginal reef

-Lower [CO32-]

-Healthy reef

-No major industries or pollution

-Natural gradient in [CO32-]

[CO32-] across

coral reef platform

Outer rim Mid-platformInshore

What can we expect in the future ?

http://ioc3.unesco.org/oanet/FAQacidity.html

The IPCC expects:

•a drop in ocean pH of about 0.4 pH units by the end of this century

•a 60% decrease in the concentration of calcium carbonate

Changes in atmospheric CO2 under the "business as usual" scenario to the year 2100 and associated changes in ocean pH and carbon chemistry. Adapted from Wolf-gladrow et al., 1999

Why is ocean acidification a problem?

Seawater acid-base balance important in regulating biological and chemical processes, e.g.:Function of enzyme and proteinsChemical reaction ratesAvailability of nutrients and trace metals

CO32- is an essential building block for marine

calcifiers depositing skeletons or shells made of CaCO3

†

Less building material equals slower growth, weaker structures (similar to osteoporosis in humans) and increased vulnerability to environmental stress in general

† Ca2+ is the other building block, but there are plenty of calcium in seawater

Ca2+ CO32-

CaCO3

The Alkalinity Anomaly Method

•The alkalinity anomaly method relies on the principle that when a calcifying organism produces a mole of calcium carbonate, total alkalinity is decreased by two moles.

•I will be able to know the exact degree to which synthesis or dissolution is taking place using this method.

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Average Hourly Daytime Rate of Calcifi-cationAverage Hourly Nighttime Rate of Calci-fication

Average Daytime vs. Nighttime Calcification Rates

The Buoyant Weighing Method

http://www.aagaines.com/man/graphics/scale.jpg

Calcification (or dissolution) of a coral sample is inferred from changes in the sample’s mass. The weight can be determined in water using the formula: Wa = Ww / [1-(pw/ps)]

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0.1

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0.8

Average Weekly Dry Weight Change (g)

Average Weekly Dry Weight Change (g)

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1.5

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3.5

Predicted Weight Change: Week 1-3Actual Weight Change: Week 1-3

AA Predicted Weight Change vs. BW Actual Weight Change

Thank You!