Studies On Environmental Impact Factors And Control Techniques Of Two Important Invasive Alien Aquatic Animals In Yunnan Province

Biological invasion has already become one of the major environmental issues of the world. It was different for many invasive species in invasive route, mechanism, damage caused and control method. Golden Apple Snail(Pomacea canaliculata) and Red Swamp Crayfish(Procambarus clarkii) are two important species of aquatic alien invasive species in Yunnan Province. The Pomacea canaliculata, native to wetlands of tropical South America(Brazil, Argentina etc.), is an amphibious freshwater snail. The Procambarus clarkii introduced from northeastern Mexico and central to south United States(Louisiana), is one of the famous invasive alien crayfish. Both of them had ever been introduced as aquaculture species by many countries and regions worldwide, as well as many provinces in China, which led to enormous economic and ecological losses. However, there were few comprehensive and systematic studies about the influence of environmental factors on these aquatic alien invasive species and their prevention and control technology.In order to understand the effects of environmental factors on the distribution of Pomacea canaliculata and Procambarus clarkii in Yunnan Province and to develop the control technology of the invasive snails and crayfishes, annual population dynamics of Pomacea canaliculata in Kunming area, effects of environmental factors on the density variation of Pomacea canaliculata and distribution of Procambarus clarkii were studied by field survey in this paper. The influence of Procambarus clarkii on native aquatic animal was also investigated through predator experiment. Chemical and biological control technology on Pomacea canaliculata and Procambarus clarkii were explored by laboratory experiment. There researches will provide a theoretical basis for their scientific control. The main results of the research are as follows:(1)The field survey in 2014 ~ 2015 showed that there were two peaks of reproductive activity periods of Pomacea canaliculata, the first was a small climax of breeding activity in May through June, and the second was the larger peak in July through August. There was different in population density in different regions. Correlation analysis between the environment variable such as water vegetation, physicochemical properties of water, other aquatic organisms and population size and multivariate regression analysis showed that the vegetation cover, pH and frequency of fish occurrence were the major environmental factors that influence the population size of Pomacea canaliculata.(2)The field survey was adopted to investigate the distribution of Procambarus clarkii by trapping method through May to July in 2015. The result showed Procambarus clarkii has invaded most of the water body in Kunming area, especially in the slow flow water body, earth-filled dam and other water bodies. Principal component analysis on habitat characteristics, physicochemical properties of water, biotic and abiotic factor showed there were four components which affect the regional distribution of Procambarus clarkii, including habitat characteristics(number of plant species, vegetation coverage, habitat complexity, width of surface vegetation, silt level); physicochemical properties of water(water depth, dissolved oxygen, calcium ion); biological factor(number of alien species); abiotic factor(human activity). The major factors were coverage of vegetation and silt level. One hand, vegetation provided rich food and sheltered, on the other hand, silting substrate was benefit for cave dwell for Procambarus clarkii.(3)Selective predatory experiment of Procambarus clarkii’s was carried out by presenting native and exotic aquatic organisms for Yunnan Province from March to July in 2015, the predation results showed that Procambarus clarkii predated native amphibian specie Beufo andrewsi significantly higher than native fish Carassius auratu, Misgurnus anguillicaudatus, native crustacean specie Macrobrachium nipponense and exotic fish Gambusia affinis. In other words, Procambarus clarkii predated native species most, especially amphibians. The larger size of Procambarus clarkii, the more kind of aquatic organisms were preyed.(4)Laboratory experiments tested the effect of chemical and biological methods on Pomacea canaliculata. The results were showed that the biopesticide tea saponin, azadirachtin, rotenone and plant ash have a certain protective effect, but the killing effect of kind of botanical insecticides at different concentration were different, the tea saponin and azadirachti achieved the better controlling effect, especially the tea saponin, when the concentration were 60 mg/l and 80 mg/l, and treated for 72 h in laboratory, the mortality of snails achieved to 100 %. The experiment of biological control experiment indicated that the four breeding aquatic animals Chinemys reevesiis, Carassius auratus, Eriocheir sinensis, Misgurnus anguillicaudatus also have a certain effectiveness on controlling snails. Which the controlling effect of C. reevesiis was the best, then the E. sinensis and C. auratus better, while the M. anguillicaudatus least, of all they achieved the best controlling effect on the small size of Pomacea canaliculata.(5)The chemical control experiment of Procambarus clarkii showed that chemical pesticide decis and biopesticide tea saponin, azadirachtin, rotenone have certain toxic effects, which azadirachtin, decis and rotenone achieved the better controlling effect, especially the azadirachtin, while the tea saponin least. We studied the controlling of Procambarus clarkii with four breeding aquatic animals C. reevesiis, C. auratus, E. sinensis, M. anguillicaudatus, and the results indicated the controlling effect of E. sinensis was the best, then the C. reevesiis and M. anguillicaudatus better, while the C. auratus least, of all they achieved the best controlling effect on the small size of Procambarus clarkii.