The Role of Light and Oxygen in Chaoborus punctipennis (Insecta: Diptera) Diel Vertical Migration

Abstract

ABSTRACT Aquatic phantom midge larvae (Chaoborus punctipennis) exhibit diel vertical migration (DVM) in response to fish visual predation, remaining in deeper waters during the day and ascending nocturnally to feed. Light penetration into the water column and dissolved oxygen concentrations are hypothesized to determine the depths where larvae are found during daylight hours. We collected samples in Yellow Poplar Tree Lake in Millington, Tennessee before and after sunset during a day in March, May, July, and September of 2005. Average daytime depth (Dc) and use of daytime refugia (dark or hypoxic waters) were significantly different (P<0.05) among larval instars (I/II<III<IV) in May, July, and September when the lake was highly stratified. Final instars utilized hypoxic waters (DO2 <3.5 mg/L) more than III instars, while I/II instars did not use this refuge. When the lake was highly stratified, the average depth of all instars during daylight hours was below the depth of maximum light penetration (1.0 μEinsteins/m2/s); IV instars remained below this level in May, July, and September, but III instars did so only in July and September, and I/II instars did so only in September. Further, IV instar Dc was significantly correlated with the critical oxygen threshold for fish (DO2=3.5 mg/L; R2=0.783, df=l1, P<0.01) but not with maximum light penetration (R2=0.183, df=11, P>0.05), indicating that oxygen was the ovemding stimulus governing C. punctipennis DVM seasonal changes and average daytime depth.