TOWARD A CHRONOLOGY OF HALIOTIS FULGENS, WITH A REVIEW OF ABALONE SHELL MICROSTRUCTURE

The microstructure of the shell of the abalone Haliotis fulgens consis ts of alternate layers of aragonite and prismatic calcium with darker organic matrix (conchiolin) that are visible as rings when the shell i s ground down at the spire. This abalone deposits about four prismatic layers in the first year and three layers each year thereafter at the site studied, Prismatic layers are laid down in about April, August a nd November, corresponding with sea temperature minima and maxima and with the spawning season. After about 3 years of age, prismatic layers at the spire of the shell begin to be lost through erosion of the out er layers of the shell. The first prismatic layers deposited are 5-10 mu m across, and later layers successively increase in thickness to a maximum of about 80 mu m. This property is used to estimate the rate o f erosion of layers, which is about one per annum. When the rate of de position and the rate of erosion are known for a locality, an estimate of the true age can be made. The findings are considered in relation to the microstructure of the abalone shell.