Uptake of Mg and Sr in the euryhaline ostracod Cyprideis determined from in vitro experiments

Abstract

This paper describes a series of in vitro experiments during which juveniles of the euryhaline ostracod Cyprideis australiensis were grown to adulthood in waters of ranging salinities (from 10–70‰.) and Mg/Ca and Sr/Ca ratios, and under two different constant temperature regimes, 20° and 25°C. Results indicate the following thermodependence for Mg in the calcitic valves of adult Cyprideis australiensis: T(Mg)=2.69+5230×[Mg/Ca] ostracod/[Mg/Ca] water. A minor thermodependence was also found for this ostracod species with respect to the uptake of Sr. There is a very strong relationship between the Mg/Ca of the ostracods and the Mg/Ca of the waters in which they moulted. The same can be said between the Sr/Ca of the ostracods and the waters' Sr/Ca. There is no direct relationship between water salinity and either the Mg/Ca ratio nor the Sr/Ca ratio of the ostracod valves. The 20° and 25°C experiments established the following partition coefficients which we believe can be applied to any Cyprideis taxa grown in waters within the 5 to 20 Mg/Ca range: K D [ Mg]=−0.000514+0.00019× Temperature °C , and K D [ Sr]=0.223+0.0086× Temperature °C . This relationship for Sr, which has been mentioned for the first time for Cyprideis is tentative. The Mg/Ca of ostracods is strongly dependant on temperature, but this effect can easily be masked by variations in the Mg/Ca of the host water commonly found in natural lakes. Ostracod physiology is adapted to constructing valves from low-Mg calcite, so when growing in waters with high (>30), or very low (<1) Mg/Ca, Cyprideis species will not take up Mg in accordance with the calculated K D.