PARENT SESSION
Contributed Oral Session 23: Aquatic Ecology: Plankton Communities
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 515 A, Level 5, Palais des congrès de Montréal

Carbon isotopic evidence for spatial segregation of planktonic food webs in a lake ecosystem.

Doi, Hideyuki ^*,1, Zuykova, Elena², Shikano, Shuichi ³, Kikuchi, Eisuke³, Ota, Hiroshi¹, Yurlova, Natalia³, ¹ Graduate School of Life Sciences, Tohoku University, Sendai, Japan² Institute of Animal Systematics and Ecology, Siberian Branch of Russian Academy Sciences, Novosibirsk, Russia³ Center for Northeast Asian Studies, Tohoku University, Sendai, Japan

ABSTRACT- Lake ecosystems have been classified as pelagic, littoral, and benthic habitats, and these habitats were coupled though the food webs. However, there is very little evidence for spatial segregation of food webs in pelagic and littoral habitats. We investigated spatial segregation in the food web of the lake ecosystem at 12-km estuarine transition zone between an inflowing river and the lake. We measured carbon and nitrogen isotope ratios of zooplankton and particulate organic matter (POM; predominantly phytoplankton) in the estuarine zone of a saline lake. In the estuarine zone, the carbon isotope ratios of POM varied among the sampling sites, and increased with increasing pH of the lake water. This may reflect a shift by phytoplankton from using CO₂ to using bicarbonate for photosynthesis with increasing pH, because bicarbonate is isotopically heavier than CO₂. The carbon isotope ratios of the herbivore and carnivore zooplankton changed along with those of the POM at each site. This indicate spatial segregation of food webs between the sites, even though the sampling sites in the estuarine zone were very close to each other. We showed a spatial segregation of planktonic food webs in the lake ecosystem.

Key words: trophic relationship, phytoplankton, zooplankton, Lake Chany