Mechanism And Effects Of Invasive Species Apple Snails (Pomacea Canaliculata) On Indigenous Species Bellamya Aeruginosa

Golden apple snail(Pomacea canaliculata) is native to the Amazon River basin of South America, which is one of 100 global malignant invasive alien species. It has caused different degree damage on China’s agricultural production, biodiversity and people’s health because of its invasion since the 1980 s, therefore proving its invasion mechanism for carrying out effective prevention and control measures and objective ecological safety assessment is of great significance. P. canaliculata as a kind of strong ecological tolerance freshwater mollusks, a large amount of excrement is likely to cause deterioration of water environment owing to its fast feeding speed, wide and miscellaneous feeding habits and large appetite. It may influence the growth and survival of native species with the similar ecological niche and win more natural resources and living space for itself by this process. This may be one of its invasion mechanisms. To test this hypothesis, a study was firstly carried out to exploit the dynamic of physicochemical properties of apple snails’ excrement feeding different kinds of food in different feeding days, Then a feedback stress experiment for P. canaliculata and Bellamya aeruginosa using apple snails’ excrement was followed. Based on the above research results, an artificial simulation experiment was developed about the chemical composition in apple snails’ excrement to further determine which chemical compositions had a great effects on growth and survival for two kinds of snails. Finally, a competition regulation experiment was designed for P. canaliculata and B. aeruginosa with apple snails’ excrement of different concentration to further verify the above hypothesis. The experimental results are as follows:1. Impact of excrement from apple snails on water quality and B. aeruginosa. Using water lettuce(Pistia stratiotes), water hyacinth(Eichhornia crassipes) and isouther naiad(Najas guadelupensis) as apple snails’(P.canaliculata) food, we tested the temperature, pH, dissolved oxygen and the concentration of ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, soluble phosphate of excrement at 1, 3, 5, 7, 9 days respectively when different number snails were bred(0, 2, 4, 8, 16, 32 only). Then a manipulative experiment was carried out to test the effects of excrement of apple snails on growth and mortality of B. aeruginosa and P. canaliculata. It was found that: apple snails’ breeding numbers and types of feeding food had a significant influence on dissolved oxygen, ammonium nitrogen, nitrate nitrogen and soluble phosphate; dissolved oxygen was significantly reduced with the increase of breeding numbers and cultivation time while the concentration of ammonium nitrogen, nitrate nitrogen and dissolved phosphate increased significantly; the nitrite nitrogen’s content was only significantly affected by breeding numbers. In the manipulative experiment, on base of relative growth and mortality rate, apple snails’ excrement had significantly different influence on P. canaliculata and B. aeruginosa; growth rate of P. canaliculata was decreased while B. aeruginosa had negative growth. Further, the mortality rate of B. aeruginosa became greater with the increasing concentration of excrement. This study shows that apple snails can indeed change the physical and chemical properties of breeding water quality through their excrement; the excrement of P. canaliculata can restrain the growth of B. aeruginosa and hasten its mortality. This limitation of excrement on native species may be an important invasive mechanism of apple snails.2. Effects of artificial simulation inorganic nitrogen and phosphorus in apple snails’ excrement on P. canaliculata and B. aeruginosa. 5 concentration gradients of inorganic nitrogen, inorganic phosphorus, inorganic nitrogen and phosphorus were set up in the experience, each concentration was repeated 5 times and the control group was established. Weighing the weight of P. canaliculata and B. aeruginosa at fifth, tenth and fifteenth day and recording the death of two kinds of snails respectively. The results showed that: effects of artificial simulation inorganic nitrogen and phosphorus in apple snails’ excrement on relative growth rate of P. canaliculata and B. aeruginosa were basically the same with apple snails’ excrement, but did not test out the lethal effects of the two snails had significant differences. This study showed that ammonium nitrogen was the main factor caused the death of two kinds of snails. Nitrate, orthophosphate, temperature, pH, dissolved oxygen and microorganisms might play a major supporting role which probably led to differentiation of relative growth rate and lethal rate between P. canaliculata and B. aeruginosa. This study further showed that the ingredients of invasive species apple snails’ excrement might indeed lead to the death of native species B. aeruginosa.3. Effects of apple snails’ excrement on competition relationship between P. canaliculata and B. aeruginosa. Using water lettuce, water hyacinth and isouther naiad as apple snails’ food, apple snails with different number were bred(0, 4, 12, 36 only), taking out the apple snails until the ninth days of culture. Then a regulation experiment was launched about competition relationship between P. canaliculata and B. aeruginosa with the harvested apple snails’ excrement. The results showed that: under the experimental conditions, the breeding frequency of two kinds of snails did not produce a significant regulatory role for the competition relationship between P. canaliculata and B. aeruginosa. However, mortality rate of B. aeruginosa was significantly higher than that of P. canaliculata due to food types and the concentration of apple snails’ excrement. The effects of apple snails’ excrement on two kinds of snails were consistent with the results of the above two experiments. This study showed that invasive species P. canaliculata could directly lead to the death of native species B. aeruginosa by its excrement for wining enough living space and resources. The results further illustrated the scientificity of the whole research.