Simulating Coral Reef Evolution

Coral reefs are one of nature's most beautiful and rich ecosystems, and rival rainforests in biodiversity. The January 1999 issue of National Geographic featured "Coral Eden" on the cover and it was a lovely article. But it also had a piece entitled "Coral in Peril". Coral reefs are very responsive to pollution, overfishing, and - highly relevant to our research at NCAR  - changes in climate.

The work shown here is an embryonic effort aimed at modeling the long-term evolution of a coral reef, starting 21,000 years ago which was at the end of the last ice age. The fundamental goal is to develop a simulation capability for the purpose of examining how changing conditions might affect the growth of a reef. The parameterizations for this effort were developed based on transects of the Great Barrier Reef.

This simulation begins 21,000 years ago, at the end of the last ice age. Over time, the continental shelfs flooded, thus creating more habitat for coral reefs, which flourished. The animation shows the temporal and coral-form evolution of the reef over time. Corals play an important role in the carbon cycle and there are quite a number of interesting ideas about possible roles they may have played in the global climate. One hypothesis is that shallow-water carbonate systems may have accounted for a big change of the CO2 seen in ice cores, corresponding to the period since the last ice age. There is also the possibility of a positive feedback loop: sea-level rises providing more habitat for coral reefs, the reefs flourish and produce more CO2, the additional CO2 causes additional temperature increase and sea-levels rise even more. It is an interesting point that  coral reefs were once an important source of CO2 released into the atmosphere, but now they account for only 1-2% of human-generated CO2.  In any event, one of the ideas central to this work is that if we can successfully simulate how reefs grew since the last ice age, we may be able to predict their evolution in the context of global change.

Global Earth System Models include vegetation models and, in the future, the inclusion of a variety of ecosystem components will probably constitute a very active and important area of research. A coral reef simulation such as the one described here could be coupled with a global model to measure its response to changing climate conditions, such as those produced by greenhouse-gas forcing. Ultimately, such a simulation could both respond and provide feedback to the overall system.

About the Visualizations

• Bathymettry: Shown in gray, this is the ocean floor upon which the coral polyps build the "reef".
• Coral Forms: There are ten different "coral forms" managed by the simulation. An individual coral form is a coral group that has been classified  by its basic form and response to various forcing functions. Each coral form  is represented by a different color.

Starting 21,000 years ago, as time progresses, sea-level rises and ultimately floods the continental shelf. The ocean floor is gray, and the 10 different coral forms managed by the simulation are each a different color. We see some coral species flourish on the steep shelf slopes, only to be replaced by a different species, presumably one that is better adapted to tracking the rapid sea-level increases. We also see a different set of species populating the shallow areas.

An alternative rendering.