Effects of temperature and chronic hypoxia on survivorship of the zebra mussel (Dreissena polymorpha) and Asian clam (Corbicula fluminea)

We examined the effects of four levels of chronic hypoxic stress at three temperatures on the survivorship of Dreissena polymorpha and Corbicula fluminea to assess the efficacy of O2 deprivation as a macrofouling control treatment and examine if critical hypoxia limits support reported distribution patterns. At 25°C, the hypoxia tolerance was examined at Po2 = 7.9, 11.9, 15.9, 23.8, and 31.8 Torr (1 Torr = 133.322 Pa) or 5, 7.5, 10, 15, and 20% of full air O2 saturation (Po2 = 159 Torr). At 15°C, the hypoxia tolerance to 7.9, 11.9, and 15.9 Torr was tested and at 7.9 Torr for 5°C treatments. For both species, Po2 and temperature influenced survivorship dramatically with increasing survivorship at higher Po2 and decreasing temperatures. At 25°C, C. fluminea experienced mortality at 7.9, 11.9, and 15.9 Torr, with LT50 values of 144, 216, and 216 h, respectively, versus 288, 384, and 480 h for the 15°C exposures. Dreissena polymorpha treatments had LT50 values of 120, 216, and 216 h at 25°C for the 7.9-, 11.9-, and 15.9-Torr treatments versus 26% mortality after 600 h and 28% mortality after 720 h at 15°C. The 7.9-Torr treatments at 5°C had LT50 values of 480 h for C. fluminea and 1056 h for D. polymorpha. This study showed that both species displayed broad seasonal variation in hypoxia tolerance and that hypoxia limits may be used to assess infestation risk.