[Coral-List] Geometry, coral bands, and tree rings

[Eugene Shinn]

Johns post on geometry of coral heads and banding width and age, is 
very interesting. It reminded me of some attempted calculations I 
made related to Acropora cervicornis growth back before computers 
came along. While doing my growth branch extension measurements in 
the early 1960s I noted that Staghorn initiated new branches during 
Feb when water temperature was lowest. The number of new branches 
ranged from 2 to 5 so I chose an average of 3 new branches to make 
some simple calculations. The results presented some 
problems/questions. They showed that if one starts with a small 
colony consisting of 10 branches and assumes that each of the 3 new 
branch would then grow 10 cms and then repeat the same each year for 
10-years the results would be 5,904,900 cms or roughly 35 miles of 
branches! At 10 cms a year and assuming upward growth the colony 
consisting of 35 miles of branches could still be no higher than 1 
meter. Now that presented a problem? Assume each 10 cm weighs 100 
grams the 5,904,900 cm of coral should weigh about 59,049 kgs. How do 
you stuff 35 miles of branches, weighing 59,049 kilos in a hemisphere 
only 1 meter high? A solid M. annularis head 1 m high likely would 
weigh no more than 900 kg. I soon realized that such unlimited growth 
had to be impossible and guessed that storms, predation and 
overcrowding or some natural pruning would prevent A. cervicornis 
from reaching its full growth potential even under the best of 
conditions.  Even given predation forced mortality or some kind of 
natural pruning seemed mandatory. Perhaps assuming 3 new branches 
each year was unreasonable but certainly two branches is not. Even at 
only 2 new branches per year there would still be substantial 
overgrowth. Could this explain why Acropora is not immortal. Maybe 
that is why fragmentation has to be the main strategy for survival? 
If so, could a long period without storm damage and fragmentation 
lead to automatic demise and/or onset of diseases? Seems like 
something has to give. I never could figure it out. Maybe someone 
using computers can come up with better calculations. Gene
Reference: Shinn, E. A., 1976, Coral Reef Recovery in Florida and the 
Persian Gulf, Environmental Geology, Vol. 1 pp;241-254, Springer 
Verlag NY.

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No Rocks, No Water, No Ecosystem (EAS)
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E. A. Shinn, Courtesy Professor
University of South Florida
Marine Science Center (room 204)
140 Seventh Avenue South
St. Petersburg, FL 33701
<eshinn at marine.usf.edu>
Tel 727 553-1158---------------------------------- 
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