Introduction to Ocean
Acidification

Introduction to Acidification's Effects on Coral

Key Physiological Characteristics of Coral

Chemistry of Coral Calcification

How is Coral Calcification Affected by Acidification?

Acidification's Effects on Other Calcifying Organisms

Introduction to Ocean Acidification

Approximately 30% of the CO2 emitted into the atmosphere is absorbed by the ocean and causes the formation of carbonic acid (Hofmann et al., 2010). This alters the pH of the entire ocean, which has already experienced a drop of 0.1 units (a rise in acidity of approximately 30%, as pH is measured on a logarithmic scale) since pre-industrial times (Doney et al., 2009, Cooley et al., 2009).

Marine calcifying organisms require the availability of calcium carbonate in order to secrete their calcium carbonate shells and skeletons (Fabry et al., 2008). The concentration of carbonic acid in the oceans is a direct result of levels of CO2 in the atmosphere, and the availability of calcium carbonate is a direct, inverse, result of the concentration of carbonic acid (Fabry et al., 2008). Thus, acidification is leading to a de-saturation of the ocean’s calcium carbonate supplies (Fabry et al., 2008). As the saturation of calcium carbonate decreases, calcification rates will decrease in calcifying organisms such as coral.

Coral reefs are not only valuable for their beauty and diversity – they also provide important ecosystem services. Island nations rely on coral reefs for both shoreline protection and tourism income (Cooley et al., 2009). If the acidic waters reach the tropics, coral reefs will begin to dissolve as they become unable to balance natural erosion processes with new building efforts (Hutchings, 2000, Erez et al., 2011). The total value of shoreline protection from reefs is estimated to be $9.0 billion a year (Cooley et al., 2009). One island nation, St. Lucia, receives $28-50 million/year in shoreline protection from reefs, as well as more than $100 million/year from reef tourism (Cooley et al., 2009). When reef systems collapse due to ocean acidification, countries such as St. Lucia will suffer dramatically.

Ocean acidification has been called the first large-scale environmental crisis we will face. We’re seeing the first effects of acidification in cold, temperate regions of the ocean, where naturally occurring upwelling processes bring dense, acidic water up from the ocean floor, exacerbating acidification due to CO2 (Fabry et al., 2008, Hofman et al., 2010, Silverman et al., 2009). As CO2 levels rise, acidification will spread worldwide.