Physiological tolerance of marine calanoid copepod eggs to sulphide

Abstract

The impact of anoxia and anoxia-sulphide (8 different numeric sulphide concentrations, ranging from 10 µmol l -1 to 10 mmol l -1 ) on hatching of subitaneous eggs of the planktonic copepod Acartia tonsa Dana was evaluated. The experiments were consequently conducted at pH 8.1. Subita- neous eggs, spawned by laboratory-reared specimens, were exposed to anoxia and anoxia-sulphide for different periods (3, 7, 14, 30, 60, 120, 180 and 240 d) and then transferred to normoxic conditions. Short-term (3 to 60 d) exposure to anoxia or anoxia-sulphide did not significantly affect the hatching success of the eggs, but hatching generally declined with increasing length of exposure. After 60 d of exposure there were significant differences between the effects caused by anoxia and anoxia-sul- phide (sulphide concentrations ≥250 µmol l -1 ). After 240 d of exposure there were significant differ- ences in hatching between eggs treated with anoxia and those with anoxia-sulphide (all sulphide concentrations). A short-term experiment, where subitaneous eggs were simultaneously exposed to oxygen and different sulphide concentrations, indicated that sulphide is capable of crossing the eggshell. The metabolic rate of eggs exposed to normoxic conditions was 1.86 ± 0.57 µJ h -1 . Eggs exposed to anoxia had a metabolic rate of 0.08 ± 0.02 µJ h -1 , whereas eggs exposed to anoxia and 14.7 mmol l -1 sulphide had a metabolic rate of 0.25 ± 0.001 µJ h -1 . Based on the metabolism ex- periments and the fact that internal egg pH was ~6, an unknown sulphide defence mechanism is suggested to be present in A. tonsa eggs.