Abstract: Autopsy of a Dead Coral Reef
During the winter of 1969-1970, Hen and Chickens patch reef (24°56^primeN, 80°33^primeW) in the Florida Keys suffered 80 to 90 percent mortality. Twenty cores from both living and dead Montastrea annularis coral heads taken from this reef with a newly developed underwater coring device, were slabbed and x-radiographed to determine the cause of the chronology, allowing annual growth rate measurements and timing of abnormalities from the present, back to 1926.
"Stress bands," formed during winter months, occur periodically between annual summer bands. Stress bands deposited by the corals under unfavorable environmental conditions in 1942, 1958, 1964, and 1970 were dated easily by direct counting of annual bands. Comparison of stress bands with U.S. Weather Bureau data shows that they correspond to unusually cold winters. The most recent stress band in all living corals at Hen and Chickens patch reef correlates with the observed time of mass mortality and a 3-day span during which maximum air temperatures were consistently below the temperature (13.9°C) known to be lethal to M. annularis. It is concluded that the death of Hen and Chickens patch reef was caused by uncommonly cold water. X-radiographs of coral cores from elsewhere in the lorida reef tract indicate that this particular event was not unique to Hen and Chickens and that, in the past, other less damaging periods of critically low water temperatures have been recorded by Florida corals.
AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA