2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 14
Presentation Time: 8:00 AM-4:45 PM

Skeletal Growth Rates in Modern Reef-Building Corals (Acropora palmata, Acropora cervicornis, Porites porites var. divaricata, and Montastrea annularis): Belize Barrier Reef

HEIVILIN, Jason A. and VIDETICH, Patricia E., Department of Geology, Grand Valley State University, 1 Campus Drive, Allendale, MI 49401, heivilij@student.gvsu.edu

The age and growth rates of hermatypic scleractinian corals can be estimated by examining annual density bands in their skeletons. In this study, in an attempt to reduce annual environmental variations between species, we concentrated on comparing growth bands in a number of coral species collected from a short (~0.5 km long) traverse across the relatively pristine, Belize barrier reef. The extant corals were collected in March/April, 1978, primarily from the back reef and reef crest near Carrie Bow Cay, 29 km offshore from Belize and in water depths of less than ~1.5 m. However, some samples were collected from the outer fore reef at a depth up to ~20 m. Top and bottom water temperature at the time of collection was consistently 25.6°C, but at that time the area had an annual range of surface water temperatures of 24-29°C. Density bands were measured both in petrographic thin sections and acetate peels. In specimens of Acropora palmata, Acropora cervicornis, Porites porites var. divaricata, and Montastrea annularis we were able to measure growth bands back four to six years. Studies of these corals show that radial growth rates differ greatly from year to year, both due to variation of calcification rates between species and either optimal, or limiting, environmental conditions such as water temperature, salinity, precipitation, and episodic events such as storms or hurricanes. M. annularis showed the highest radial growth rates (up to 4 mm) among the species examined, whereas P. porites var. divaricata showed the least variation in growth rates (1-2 mm). In general, although the growth rates vary from species to species, the variation in growth rates can be correlated through time. For example, for each species the lowest growth rate was during 1974-75, perhaps due to Hurricane Fifi, which struck the area in September, 1974.