Mg / Ca ratios in the shells of cultured specimens and natural populations of the marine ostracode Xestoleberis hanaii (Crustacea)

We studied Mg / Ca ratios in the shells of the shallow-water ostracode Xestoleberis hanaii Ishizaki, 1968 [Ishizaki, K., 1968. Ostracodes from Uranouchi bay, Kochi Prefecture, Japan. Tohoku University Science Report, Second Series (Geology) 40 (1), 1-45.] in laboratory-cultured and field-collected samples. X. hanaii was cultured in our laboratory from A-7 to adult stage under controlled temperatures (15-28 °C). Results of the culture experiments show that the Mg / Ca ratio of X. hanaii is strongly correlated with water temperature within the temperature range of 15-28 °C. In the field-collected samples, seasonally fluctuating Mg / Ca ratios of their shells parallel the variation in the seasonal seawater temperature, and the water temperature estimated from the mean value of the adult stage samples collected on any given date agreed quite well with the average water temperature for the period of 8 days prior to the collection date. Based on the changes in Mg / Ca ratios and shell morphology in the course of ontogeny, we suggest that Mg is contained in the organic matter, which is one of the shell components that form the network or the framework within which the calcite crystals are formed.