Contribution Of Microcystis To Food Webs

For the past few years,stable isotopes of carbon and nitrogen,as a powerful approach to study the structure and dynamics of food webs and trophic relationships, have been increasingly used in the studies on a wide variety of ecosystems and become one of the most effective and useful method in aquatic ecology studies.In this thesis, stable isotopes of carbon and nitrogen were used to study the contribution of Microcystis to food webs in Meiliang Bay of Lake Taihu.The structure of food webs and trophic levels were studied during the period of Microcystis blooms in Lake Taihu.The carbon and nitrogen stable isotope values of fishes,zooplankton,benthic animals,Microcystis,macrophytes and periphyton were analyzed during the experiment.The result showed thatδ¹³C of the samples ranged from -28.44‰to -19.88‰.And there were no evident and stable enrichment.δ¹⁵N values ranged from +12.36‰to +25.68‰,and they were enriched from low trophic level to the higher trophic level.It covered a large extent of theδ¹³C andδ¹⁵N values in Meiliang Bay, indicating a large and various food sources,δ¹⁵N of the sample in Lake Taihu was much higher than other lakes reported before.Microcystis were part of the carbon source of bighead carp,silver carp,zooplankton and Chironomus based onδ¹³C data.δ¹³C of Myriophyllum verticillatum and periphyton on Myriophyllum verticillatum were differential from each other,which indicated a different food source for periphyton on Myriophyllum verticillatum other than Myriophyllum verticillatum.δ¹⁵N values indicated that zooplankton were the main food source(account of 37%～94%of the food ratios) for Protosalanx hyalocranius and other few kinds of fishes and Palaemon modeslus.¹³C-labeling experiment was conducted to evaluate Microcystis as carbon resource for crustacean plankton in Lake Taihu during November,2006.A polyvinyl chloride (PVC) cylinder enclosure was set in the hypereutrophic Meiliang Bay(Lake Taihu, China).Labeled Microcystis were killed with hydrochloric acid and added to the cylinder (10⁶ cell 1^-1).Zooplankton,particulate organic matter(POM) and bacteria were collected. ¹³C of bacteria were overprinted by the labeled Microcystis as soon as they were added in the enclosure.Crustacean plankton accumulated ¹³C shortly after ¹³C appeared in POM and bacteria.Microcystis detritus and the attached bacteria seemed to be utilized by crustacean plankton as an important food source in Lake Taihu.During the simulative experiment,the flow of carbon and nitrogen source of Microcystis in aquatic food webs were studied from carbon and nitrogen double labeling measures.Zooplankton,Chironomus,Limnodrilus,Radix,Bellamya,larvae and adults of P.modeslus were collected during the experiment.It was approved fromδ¹³C andδ¹⁵N values that substance and energy from Microcystis could be utilized by other aquatic creatures.During the experiment,zooplankton,larvae of P.modeslus and Radix could make a good usage of the substance and energy from Microcystis.Other aquatic creatures could also make use of carbon and nitrogen source of Microcystis in a way.Regardless of the way and mechanism,Microcystis carbon resource being utilized by zooplankton may be a common phenomenon in Lake Taihu and other lakes with Microcystis blooms and a low abundance of other food resources.However,the mechanism of Microcystis carbon resource being utilized by other aquatic creatures was not clear.The contribution rate of Microcystis detritus and the attached bacteria to other aquatic creatures need further study. Bacteria attached on the Microcystis detritus may improve the food quality in Lake Taihu, and they may play an important role in the trophic process.