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 th ree temperatures on the survivorship of Dreissena polymorpha and Corbi cula fluminea to assess the efficacy of O-2 deprivation as a macrofoul ing control treatment and examine if critical hypoxia limits support r eported distribution patterns. Al 25 degrees C, the hypoxia tolerance was examined at Po-2 = 7.9, 11.9, 15.9, 23.8, and 31.8 Torr(1 Torr = 1 33.322 Pa) or 5, 7.5, 10, 15, and 20% of full air O-2 saturation (Po-2 = 159 Torr). At 15 degrees C, the hypoxia tolerance to 7.9, 11.9, and 15.9 Torr was tested and at 7.9 Torr for 5 degrees C treatments. For both species, Po, and temperature influenced survivorship dramatically with increasing survivorship at higher Po-2 and decreasing temperatur es. At 25 degrees C, C. fluminea experienced mortality at 7.9, 11.9, a nd 15.9 Torr, with LT50 values of 144, 216, and 214 h, respectively, v ersus 288, 384, and 480 h for the 15 degrees C exposures. Dreissena po lymorpha treatments had LT50 values of 120, 216, and 216 h at 25 degre es C for the 7.9-, 11.9-, and 15.9-Torr treatments versus 26% mortalit y after 600 h and 28% mortality after 720 h at 15 degrees C. The 7.9-T orr treatments at 5 degrees C had LT50 values of 480 h for C. fluminea and 1056 h for D. polymorpha. This study showed that both species dis played broad seasonal Variation in hypoxia tolerance and that hypoxia limits may be used to assess infestation risk.