STUDIES ON SHELL FORMATION. I. MEASUREMENT OF THE RATE OF SHELL FORMATION USING Ca45 ,

Abstract

1. The rate of shell formation in the oyster Crassostrea virginica Gmelin has been determined by measurements of Ca⁴⁵ deposited by oysters placed in sea water containing Ca⁴⁵. The experiments were carried out at Beaufort, N. C., during May and June at 21.2 to 25.4° C. Radioactivity measurements were made directly on the inner shell surface. 2. The mean amount of deposition was directly proportional to the time of exposure to Ca⁴⁵ for 8, 16 and 24 hours. Growth increments occurring in four hours were measurable. Individual variation in the rate of deposition was marked. 3. The mean rate of deposition in the posterior region of the shell was approximately twice that in the center and anterior regions. Within a general region local areas may exhibit a still greater difference in rate. From the average radioactivity per unit area of shell surface the total amount of CaCO₃ deposited in a given period can be calculated. 4. Shell from which all tissue had been removed became increasingly radioactive in sea water containing Ca⁴⁵ as a result of exchange. The magnitude of exchange was relatively very small as compared with active deposition by the oyster. 5. Advantages and limitations of the isotope method for measurements of growth are discussed.