396 THE BIOLOGY OF HYDRA : 1961 



irradiated. Since it was a high energy photon I beUeve it was not 

 attenuated much by the water. 



GOREAU: Are there other criteria for measuring age? Two years 

 ago we measured the effect of size on specific calcification rates on 

 a free hving coral where size was an indication of age. In this 

 particular species, Manicina arcolata, we found a progressive reduc- 

 tion in the calcification rate (per mg. of protein nitrogen) as the 

 colonies got larger. The difference between the smallest (50 mg. ) 

 and the largest ( 149 g. ) colonies tested was almost two orders of 

 magnitude (Goreau, T., and N. Goreau. 1960. Biol. Bull 118:419). 

 Now, it is interesting that these particular corals hardly ever grow 

 beyond 500 grams. This may have some ecological significance 

 for if the individuals get much larger and heavier than that they 

 may sink into the sediments since most of them are not attached. 

 However, many other species of corals do not show such a regulated 

 growth pattern. I suspect that some species grow indefinitely. 



STREHLER: The maximum ages for corals which are quoted 

 in Comfort's excellent book (which I recommend to those of you 

 who might be curious about senescence) is only about 28 or 30 

 years. Now this is based upon size estimates. 1 would be delighted 

 to see somebody try to find a better index of age than simply size. 



GOREAU: On the basis of some of the accretion data which I 

 referred to in my talk on Thursday, I calculated that corals weigh- 

 ing about 200 tons may be as much as 800 years old. 



STREHLER: You think these come from a single individual? 



GOREAU: Not necessarily, but the specimens used in our experi- 

 ments were clones descended from single planulae. 



STREHLER: The difficulty here is that this is more like a hydra 

 clone, it seems to me, than an individual animal. 



GOREAU: Some corals, like the branching species, have an in- 

 determinate growth pattern and can probably be considered im- 

 mortal, because they can grow as long as there is room. This is 

 probably not true of the massive ones in which the skeletal mass 

 would increase much faster than surface area. These would col- 



