Responses of the New Zealand green-lipped mussel, Perna canaliculus, to acute environmental changes designed to depress metabolism

We explored the behavioural and physiological responses of adult green-lipped mussel, Perna canaliculus by assessing synchronous measurements of mussels' cardiac activity and gaping pattern as a proxy for metabolic activity in response to decreasing temperature, oxygen concentration, or increasing anaesthetic (MgCl2) concentration. We found that gaping magnitude of P. canaliculus, declined with decreasing temperature from 14 degrees C to 4 degrees C, with a corresponding decrease in heart rate (HR) by up to 80%. In contrast, the mussels maintained constant HRs and increased gaping magnitude with declining oxygen concentration (i.e., 8 mg O2 L-1 to 1 mg O2 L-1), with a depression of HR (i.e., 20% reduction from starting condition) only evident at 0.5 mg O2 L-1, suggesting that this species is very tolerant to hypoxic conditions. MgCl2 concentration of 30-50 g L-1 appeared to increase valve gaping and depress metabolic rate significantly as reflected in an increased relative gaping magnitude of up to 84% and a decreased HR of up to 80% respectively. These results reveal that onset of metabolic depression of P. canaliculus can be triggered below 10 degrees C, oxygen levels below 1 mg O2 L-1 and MgCl2 concentrations above 30 g L-1. Such conditions are likely to decouple the species from external disturbances and may have application potential to minimize the loss of this aquaculture species due to stress associated with harvesting and handling processes.