The larvae of the phantom midge Chaoborus (Diptera: Chaoboridae) is well known to play important roles affecting species distribution and abundances as major predators in freshwater planktonic food webs. They are distributed worldwide as 14 species in Holarctic region and are known as an omnivorous invertebrate predator to eat small zooplankton species. Since Chaoborus species has never been reported and studied in Korea, we studied basic taxonomical and ecological aspects of this species. We collected Chaoborus samples from Sang-Chun reservoir located near Lake Chungpyung.
First of all, we attempted to identify these samples to the species level using morphological characteristics and mitochondrial COI gene sequences. As a result, we identified those samples as Chaoborus flavicans. Also, we compared distribution of C. flavicans, D. rosea and chlorophyll a to observed seasonal dynamics. The increase of C. flavicans was observed 1-2 weeks after the increase of D. rosea. Survey of diel vertical migration patterns in summer season showed that C. flavicans were in hypolimnion at daytime, but it moved to the epilimnion at night. Finally, to determine trophic relationships in Sang-Chun reservoir, additional studies were investigated to food web studies by combining the two methods of stable isotope analysis and fatty acid (FA) analysis. For the stable isotope analysis, we observed that Chaoborus I-II instars were expected to filter feeder according to carbon isotope value. Chaoborus III-IV instars were confirmed that trophic level was higher than other zooplankton by nitrogen isotope value. We believe that basic researches on this interesting freshwater species can be continued and make an significant contribution to the advance of limnological study in Korea.
