Behavioral Responses of Chironomus Tentans to Stress as Determined By an Optical Fiber Monitoring System.

An optical fiber-light interruption biomonitoring system has been developed to examine the activity of aquatic invertebrates. It has been used to detect changes in the behavioral pattern of a tubiculous midge larva, Chironomus tentans Fabricius (Diptera: Chironomidae), that would either indicate stressful or prelethal conditions. When movement patterns of C. tentans are monitored by the system, three distinct patterns of phases are revealed: respiratory undulations, crawling and turning movements and rest or immobility. Results show that the rates and duration of movements are controlled by dissolved oxygen and temperature. A reduction in the larval undulatory rate was observed when the temperature was lowered whereas an increase in its rate was noted when the dissolved-oxygen concentration was reduced to a lower level. On the other h and , low pH levels did not alter the rate but decreased the amount of time the larvae spent undulating as they were exposed to either pH 2 and pH 4. An increase in the "escape" response of the larva was also noted at low pH's. Larvae exposed to pH 2 died within a day whereas those exposed to pH 4 died within 8 days. These results show that the biomonitoring system is capable of detecting changes in the behavior of the larva as it is exposed to lethal acidic conditions and when the larva is under stress, i.e., low dissolved oxygen and high temperature. Significant changes in the fourth instar's behavioral pattern such as increased percent of time spent undulating and "escape" response that indicated stressful and prelethal levels of chromium were identified and correlated with the concentration affecting the first instar, the least tolerant life stage of the midge. The lowest concentration of chromium at which the fourth instar behaved abnormally was at 0.1 ppm, which is the accepted concentration for chromium (EPA (1976). This concentration of chromium is lower than the 48hr EC50 for the first instar (5.8ppm).PhDEcologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158805/1/8214971.pd