38 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



situation protected from the full force of the breakers. We now find that 

 A. muricata is very sensitive to heat and correspondingly so to the smothering 

 effects of silt, and it is interesting to see that Dr. Shiro Tashiro found upon 

 testing these corals in his "biometer," which detects very minute amounts 

 of CO,, that the metabolism as measured by CO, production in Acropora 

 muricata is much more rapid than in the "mud coral" Siderastrea radians. 



In general, table 10 seems to indicate that the more resistant a coral is 

 to asphyxiation the higher its death temperature, but Favia fragum and 

 Maandra areolata have lower death temperatures than one would expect 

 from their very considerable resistance to asphyxiation. 



A clew to an explanation of this matter appears, however, if we heat the 

 corals while they remain buried under the mud. Under these conditions, 

 Acropora, Orbicella, and Pontes die at temperature 0.4 to o.i° C. lower than 

 if heated in open sea-water; but Favia, Mceandra, and Siderastrea withstand 

 heat when buried about as well as they do if in the open sea. It seems, then, 

 that Favia, Mceandra, and Siderastrea can live at a reduced rate of metab- 

 olism, and being buried puts them into a condition resembling hibernation 

 in which heat has but little power to raise the rate of their vital processes. 

 On the other hand, the pure-water corals Acropora, Orbicella, and Pontes 

 have little or none of this capacity for adjustment but must maintain a 

 nearly constant rate of metabolism. Thus heat becomes more effective in 

 killing them if partially smothered by the mud than if they be in pure 



open water. 



If this explanation be valid, Winterstein's explanation of the manner in 

 which heat depression is produced may be correct. In order to test this 

 matter more fully, however, experiments should be conducted upon some 

 animals which do and others which do not hibernate and their rates of metab- 

 olism at various temperatures and under various conditions of oxygen-supply 

 should be quantitatively determined. 



But to return to the discussion of the corals of Maer Island, Montipora 

 ramosa does not occur on the southeast reef, but it is the dominant coral of 

 the inshore muddy grass-flats on the middle of the northwest side of the 

 island, where it often completely covers areas hundreds of square feet in 

 extent. If buried beneath the mud for 24 hours it is usually killed, although 

 it can occasionally survive this treatment, but with serious injury. It 

 seems, however, that this coral is protected from the mud by the roots of 

 the sea-grass, Posidonia, which grows in association with it and which binds 

 the mud together and tends to prevent its being churned up into silt. Thus, 

 Montipora ramosa is often laid bare for 2 hours or more at the low spring 

 tides. Experiments show, however, that being soft and porous it absorbs 

 water from the moist mud around it and this enables it to survive. If dried 

 in the sun without permitting its basal parts to rest in water, it is nearly 

 killed by being exposed for \\ hours to sunlight, the dry-bulb temperature 

 being 30.35 C. and the humidity 83.5 per cent. 



