Coral Reef Diversity: Past vs Present

This topic submitted by Maria Gausman at 9:03 PM on 6/10/03.

This foursome explored Lighthouse Cave on San Salvador, Bahamas. See other beautiful phenomena from the Bahamas.

Tropical Field Courses -Western Program-Miami University


Coral reef ecosystems are the pinnacle of biodiversity in the natural world. Approximately 25% of all marine species inhabit coral reefs, where the number of individual species may be as high as one million.(1) Coral reefs of the Caribbean contain as many as 61 individual coral species, and up to 1500 individual fish species.(2) Many human populations around the world are dependant on the products of coral reefs for food, income, recreation, and shoreline stability. Although coral reef ecosystems cover only 1% of the total earth surface, the areas of the world in which they are found are also the areas of the world where the greatest growth in human population is occurring.
In recent years it has become apparent that coral reefs all over the world are in danger. Loss of species diversity has been reported in the western North Atlantic with the demise of Acropora cervicornis, a once dominant branching coral.(3) Bleaching of corals is a phenomenon that is spreading worldwide. Over the next forty years, as much as 70% of tropic and subtropical coral reefs will be wiped out.(4)
The need for conservation efforts is obvious. There are a lot of organizations chartered to preserve, restore, and find sustainable uses of coral reefs. In order to fulfill their purpose, the scientists involved with these organizations do not have a wealth of historical information about coral reef ecology to guide them. Pioneering studies on coral reefs did not begin until the late 1950s.(5) By that time, coral reefs may have already been exhibiting symptoms of trouble. To understand what a truly healthy, anthropogenically unaffected reef was like, scientist may have to look back thousands of years into the fossil record.


The fossil record may provide conservationists with a benchmark to work towards for coral reef restoration. There have been numerous studies already in western North Atlantic that focused on making comparisons between fossil reefs and modern reefs. Holocene and Pleistocene fossil reef exposures have been studied in San Salvador (1998), Barbados (1992), Papua New Guinea (1996), and Florida (1998).(6) These exposures have provided a snapshot of what a local coral reef community was like prior to any human induced stresses.
This research project will explore a coral reef community in Cockburn Town, San Salvador and compare it to a modern coral reef close by. I will look at community composition at both sites and make comparisons between them. The comparisons will determine if community composition has changed over time, and if the change has caused an increase or decrease in coral species diversity.


Fossil Coral Reef
Physical collection of fossil specimens done by myself and other students will be organized with transects.
Photographic collection will also be done within transects. Both types of collections will be analyzed by referencing identification tools such as:
*NMITA (Neogene Marine Biota of Tropical America) Internet identification tool(7)
*National Audubon Society: Field Guide to North American Fossils(8)
Specimens will be identified to the lowest possible taxa, preferably to the species level. Totals of specimens, individuals per taxa, and taxa will be recorded.

Modern Coral Reef
Since physical collection of specimens will not be possible, this entire collection will be photographic. Dead coral as well as living coral will be considered in the collection. Identification of specimens will be done by referencing photographs found on the class syllabus website. (9) Data records will be produced in the same manner as the fossil reef survey.

Data Analysis

Community composition for both sites will be determined by calculating percentages of individual taxa that make up the community. This will be done by dividing the sum of individuals within taxa by the total specimens for the site and multiplying by 100. Pie charts of the community composition for each site will be developed from these results. The modern coral reef site will be divided into “Life Assemblage Community” and “Death Assemblage Community”.
Species diversity for each site will be determined by finding the total number of individual taxa collected from each site. Higher diversity will equal a high number of individual taxa.


Greenstein et al have studied the fossil reef at Cockburn Town in 1998. The purpose of that study was to find a precedent in the fossil record of die-offs of Acropora cervicornis. They showed that no such precedent exists, so that what ever is killing Acropora cervicornis in the Caribbean Province is a modern problem.
This study will also examine the fossil reef at Cockburn Town, but the purpose here is to look more holistically at the assemblages and define what changes in overall community structure has occurred since the Pleistocene. Multiple species will be identified and assembled into profiles that describe the reefs in general. The profiles will be compared for differences and similarities. The profiles will also show how species diversity has changed with changing community structure.
Perhaps the next steps could be to use such profiles to categorize coral reefs by varying degrees of healthiness. Research of this kind can have some very practical uses for conservation ecology, an excellent link between paleontology, applied ecology, and conservation.


1 Davidson, O.G., The Enchanted Braid: Coming to Terms with Nature on the Coral Reef, John Wiley & Sons, Inc. 1998 (p5-6).

2 Conservation International, Biodiversity Hotspots, 2003:

3 Greenstein, B.J. et al, Shifting ecological baselines and the demise of Acropora cervicornis in the western North Atlantic and Caribbean Province: a Pleistocene perspective, Coral Reefs (1998) 17:249-261

4 Population and the Environment: The Global Challenge, Population Reports. Series M, Vol. XXVIII, No. 3, Fall 2000. The Johns Hopkins School of Public Health:

5 Greenstein, B.J. et al, Shifting ecological baselines and the demise of Acropora cervicornis in the western North Atlantic and Caribbean Province: a Pleistocene perspective, Coral Reefs (1998) 17:249-261

6 Greenstein, B.J. et al, Shifting ecological baselines and the demise of Acropora cervicornis in the western North Atlantic and Caribbean Province: a Pleistocene perspective, Coral Reefs (1998) 17:249-261

7 NMITA (Neogene Marine Biota of Tropical America), 2003,

8 National Audubon Society: Field Guide to North American Fossils, Alfred A. Knopf, Inc. 1997

9 Pictures and Research from Summer Field Courses: Tropical Marine Ecology of Florida, Everglades, and Bahamas, 2003,

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