Effects of waterborne iron on growth, reproduction, survival and haemoglobin in Daphnia magna

Abstract

1. The effects of waterborne iron (FeCl 3 × 6 H 2O) on growth, reproduction, survival and haemoglobin content in Daphnia magna were studied from subnormal to toxic concentrations in hard reconstituted water. 2. Low concentrations of iron stimulated reproduction and haemoglobin synthesis after chronic exposure for 21 days. Maximum reproduction occurred between 0.1 and μg Fel −1. 3. Juvenile growth was not stimulated by iron but was slightly inhibited between 1 and 8 μg Fe l −1 and above 128 μg Fe l −1. A slight inhibition of growth persisted for 21 days. 4. Total haemoglobin content was above the control with no waterborne iron at all but one concentration (512 μg Fe l −1). The highest value (3.8 × control value) was found at 2μg Fe l −1. The haemoglobin content decreased between 64 and 512 μg Fe l −1 and increased at higher concentrations. The decrease coincided with an inhibited reproduction. The increase was found in non reproductive survivors. 5. A comparison with a previous study in D. magna suggests that ambient conditions (hardness and pH) and ageing of the water are important for the effects of waterborne iron. At a hardness of 250 mg l −1 as CaCO 3 and a pH range of 7.0–8.0 the ZEP (Zero Equivalent Point) for reproduction was 158 μg Fe l −1. Continuous exposure to higher concentrations is expected to lead to extinction of a D. magna population.