Sutor, M. M. National Marine Fisheries Service, email@example.com
Ramcharan, C. M. Louisiana State University,
DENSITY-DEPENDENT PREDATION EFFECTS OF FOURTH-INSTAR CHAOBORUS TRIVITTATUS ON A FRESHWATER ZOOPLANKTON COMMUNITY
An enclosure study was conducted in Ranger Lake (south-central Ontario, Canada) from July 4 to August 5, 1997 in order to determine the effects of predation by the fourth-instar larvae of the phantom midge fly Chaoborus trivittatus on the zooplankton community. Zooplankton assemblages were established in twelve enclosures (2 m diameter and 7.5 m deep). Three densities of fourth-instar C. trivittatus (0/L, 0.1/L, and 0.5/L) were introduced as predator treatments to the enclosures. Temperature, dissolved oxygen, and zooplankton community composition were monitored for six weeks. A repeated measures multivariate analysis was performed on percent biomass of Bosmina and calanoid copepods. There was no evidence of significant differences in mean taxon biomass among predator treatments. These results differ from pervious enclosure experiments. The use of deeper enclosures and a predator species which vertically migrates may have given the zooplankton a spatial-temporal refuge which is more consistent with natural conditions. Crop content analysis of C. trivittatus showed that Bosmina constituted 88-98% of the prey items found in the crops. This supported previous laboratory investigations of prey preference and vulnerability.
Day: Thursday, Feb. 4
Location: Sweeney Center