ESTIMATION OF OYSTER GROWTH RATE FROM THE SPATIAL DISTRIBUTION OF Mg/Ca RATIO IN THE SHELLS: FOR APPLICATION TO THE ASSESSMENT OF COASTAL MARINE SECONDARY PRODUCTIVITY

Abstract

 The assessment of secondary productivity is important in terms of proper conservation of biodiversity and fishery management. The object of this study was to evaluate the potential of evaluating the growth processes of oysters, which are one of major secondary producers in coastal marine systems, by shell analysis. Using linear regression analysis, we estimated the relationship between the Mg/Ca ratio of the chalky substance in oyster shells and water temperature. It was also found that one chalky layer was formed in about two month, and the Mg/Ca ratio in the layer reflects the water temperature with timelag one month. The area around the umbo surrounded by a continuous foliate layer from both surfaces of the right shell, including the chalky substance near the umbo, which is considered to record growth, showed a positive relationship with three growth indicators of oyster individuals, shell thickness, shell height and shell cut surface area. Thus, the area around the umbo can be useful, quantitative indicators of oyster growth. These results suggest that comparing the Mg/Ca ratio distribution of the chalky substance near the umbo with field water temperature data, ones can estimate the growth process of oysters at approximately one month resolution.