Physiological and behavioral responses of the invasive amphipod, Dikerogammarus villosus, to ammonia

We studied the physiological and behavioral responses of the Ponto-Caspian amphipod Dikerogammarus villosus during exposure to four total ammonia concentrations (NH3+NH4+; TotAmm): 0.003 (control), 0.06, 1.6, and 7.0mmol L−1 (0.042, 0.84, 22.4, and 98.0mg L−1) for a period of up to 12h at 21°C. During the transition period from the control to treatment concentration as well as during the first hour of exposure to 0.06 and 1.6mmol L−1, gammarids increased their locomotor activity, which was manifested in significantly higher routine metabolic rates compared to control conditions. At control conditions, the resting metabolic rate amounted to 0.98±0.26mW g−1 and significantly increased by 19 and 37% at 0.06 and 1.6mmol L−1, respectively. The highest examined [TotAmm] caused a rapid and significant increase in resting metabolic rate by 37% within the first 4h of exposure before gammarids died. The exposure to elevated [TotAmm] also resulted in a significant decreased RNA:DNA ratio and significantly higher glycogen concentrations compared to the control. We conclude that even a short exposure to TotAmm of 0.06mmol L−1, which may occur in natural habitats, disturbs the physiology and behavior of D. villosus and leads to increased metabolic costs of the maintenance and reduced protein synthesis.