176 



Papers from the Department of Marine Biology. 



in the dark for more than 7 hours without oxygen and under this con- 

 dition it produces no appreciable amount of COo. In other words, 

 these coelenterates can, if deprived of oxygen, suspend their metabo- 

 lism for a more or less protracted period without apparent injury. 



Moreover, I find that a constant high temperature causes death in 

 the same time, whether the sea-water surrounding the corals has the 

 normal concentration of about 4.3 c.c. oxygen per liter, or the oxygen 

 be supersaturated at 6.6 c.c. per liter, or reduced by being placed under 

 an air-pump to 1.7 c.c. per liter. Apparently, therefore, there is no 

 direct relation between the oxygen supply and the death temperature. 

 The death temperature also remains the same whether the corals be 

 in sunlight or in darkness. 



Using Winkler's method, tests were made upon five of the common 

 reef corals of Tortugas to determine their relative rates of consump- 

 tion of oxj^gen. In these experiments the corals were kept in the dark 

 to prevent photosynthesis in their commensal plant-cells, for in sun- 

 light the surrounding water soon becomes supersaturated with oxygen 

 from this cause. Care was also taken to use very small specimens of 

 the various species of corals and to place them in large glass jars her- 

 metically sealed, each containing about 2 liters of sea-water. The 

 corals were kept for 5 hours in these jars in darkness in a water thermo- 

 stat at 28.5° C. and daily experiments were made upon each of them for 

 11 successive days. The polyp-bearing area of each coral was then 

 determined by a planimeter and the relative weight of living substance 

 per square centimeter was obtained by killing specimens of these corals 

 in formalin, hardening in alcohol, and then dissohdng away the cal- 

 careous substance in nitric acid and weighing the tissue in sea-water. 

 Prepared in this manner a square centimeter of the animal substance of 

 Acropora ??rwnca to weighs 0.032 gram; while Orbicella annularis weighs, 

 0.17, Favia fragum 0.059, Mceandra areolata 0.109, and Siderastrea 

 radians 0.125 gram per square centimeter. 



The experiments showed that Siderastrea radians at 28.5° C. con- 

 sumes 0.0032 c.c. of oxygen per square centimeter of its polyp-bear- 

 ing surface per hour, and as each square 

 centimeter of the fleshy substance of *S'. radi- 

 ans weighs 0.125 gram, each gram of animal 

 matter of the coral consumes 0.0256 c.c. of 

 oxygen per hour, the oxygen being meas- 

 ured at 760 mm. pressure and 0° C. Thus 

 taking the behavior of S. radians as a stand- 

 ard and calling its oxygen consumption per 

 gram of its living substance 1, the relative 

 rates of oxygen consumption per hour in 



the other corals at 28.5° C. per gram of living substance of the coral 

 are as shown in the table herewith. 



