CS36 Ultraviolet Radiation
Date: Friday, June 14, 2002
Time: 10:45:00 AM
Location: Sidney
PersaudAD, York University, North York, Canada, limno_girl@yahoo.ca
Yan, N, D, York University , North York, Canada, nyan@yorku.ca
Despite their vulnerability to fish, Chaoborus larvae may be absent from low DOC fishless lakes. To determine (1) whether visible and/or ultraviolet radiation can affect Chaoborus survival in such lakes and (2) quantify lethal light doses (LD50), we conducted experiments in Ruth Roy Lake, Ontario. The lake has no fish, little DOC and few Chaoborus. Larvae were apportioned among 3 treatments: quartz (UVR + visible light exposure), OP3 acrylite (visible light only exposure) and dark controls. Replicate exposures were run at 4 depths over 2-4 day periods in July and August, 2001. The Chaoborus were highly susceptible to UVR. 100% mortality of 3rd and 4th instar larvae was observed within 2 and 4 days, respectively, at all depths. Mortality in the visible light treatment was low and did not differ (p>0.3) from dark controls. Highly significant linear relationships were generally found between larval survival and total UVR doses. LD50s ranged from 208.29 13.15 mW/cm2 for late 4th instars to 130.29 7.79 mW/cm2 for 3rd instars. The “law of reciprocity” holds for Chaoborus since survival rates were similar at the different depths.