Coral Reef Community Calcification and Metabolism Completed

Sources/Usage: Public Domain.

Ocean acidification

As carbon dioxide (CO₂) increases in the atmosphere, CO₂ is absorbed by the surface water of the ocean where it combines with water (H₂O) to make a naturally occurring, weak acid called carbonic acid (H₂CO₃). This process, called ocean acidification, results in an increase in the acidity of seawater (and a decrease in pH). A number of experimental and modeling studies (e.g. Kleypas et al., 1999; Marubini and Atkinson, 1999; Langdon et al., 2000; among many others) indicate that ocean acidification will result in a decrease in rates of calcification by reef organisms, and an increase in dissolution of reef sediments that form the foundation of reef structure. A 40% decrease in coral reef calcification has been hind-cast between the years 1880 and 2065. The severity of the impact to coral reefs will depend in part upon the balance between calcification (production of reef structure) and dissolution of reef sediments, and whether or not reef systems will be able to keep up with rising sea level.

USGS coral reef studies (Yates and Halley 2003, 2006a and b, Yates et al. 2007) have focused on quantifying reef health in terms of basic processes such as their ability to grow and keep up with rising sea level, and on the response of these processes to changes in seawater chemistry that result from climate change and ocean acidification. Results of these studies indicate that by the year 2100, net sediment dissolution may exceed carbonate production at reef ecosystems in Florida, the Caribbean, and the Pacific resulting in degradation of coral reefs, loss of fish habitat, and increased coastal erosion. Assessing the resiliency of reefs to climate change and preparing coastal resource managers for the inevitable effects of climate change and rising sea level requires a comprehensive look at past, present, and future coral reef calcification and growth rates in response to elevated atmospheric CO₂ and changing ocean chemistry.

This task focused on forecasting and hind-casting the future and past response of coral reef calcification and growth to changes in seawater carbonate chemistry from pre-industrial time to the year 2100 by:

1. Determining modern-day rates of coral reef community calcification relative to ocean chemistry,
    
2. Measuring the response of coral reef community calcification to future, elevated levels of carbon dioxide and lower pH through experiments performed in natural reef habitats, and
    
3. Reconstructing past changes in seawater pH relative to coral growth rates using stable isotope geochemical techniques (δ¹¹B and δ¹⁸O) and changes in coral skeletal density in coral skeleton cores.

This task was developed in partnership with NOAA, NCAR, University of Miami-RSMAS, and USF; with collaborators from UPR, the Buccoo Reef Trust, Tobago House of Assembly, Caribbean Coral Reef Institute, and University of the West Indies. Results of these studies will support work of partnering agencies to develop predictive capabilities for quantifying the impacts of elevated pCO₂ on coral reefs.