| Worldwide,invasive species have caused the decline of native populations and regional extinctions,the reduction of economic crops,and the widespread epidemic of zoonotic diseases and economic species infectious diseases.Invasive species has become a major ecological event affecting economic development and public health.Pomacea canaliculata is one of the first 16 vicious invasive species to invade our country.Since it was introduced and abandoned in our country in the 1980 s,it has caused a series of major ecological problems.P.canaliculata has a large appetite and mixed eating habits.It can directly feed on a variety of native plants,and can also directly prey on animals in the native ecosystem when they are hungry,leading to the regional depletion of the native plants.When the resources of food and dissolved oxygen in water in the ecosystem are exhausted,the native animals will also die of starvation or lack of oxygen.In addition,as a malignant invasive species,P.canaliculata has some special life strategies.For example,it will produce food debris during eating and excrete a large amount of it into the water body.These excretions and secretions can stimulate the physical and chemical properties of the water body,and then affect the microbial and plankton communities in the water body,and even cause eutrophication of the water body,which will affect the survival of the species with similar niche to the P.canaliculata,and create opportunities for P.canaliculata to kill other native species and seize their empty niches.However,there are many biological processes in the local ecosystem that can lead to the change of water environment.Among them,bioturbation plays an important role.The native bioturbators such as Limnodrilus hoffmeisteri and larvae of Chironomus sp.can enhance the material and energy exchange between the overlying water and sediment,so that change the solid particles and the content and existence of nitrogen and phosphorus at the sediment-water interface.This effect will also change with the density and species of the benthic animals.The excrement of snails contains uric acid or the nitrogen in the form of ammonia nitrogen,a large amount of secretions and excrements of P.canaliculata cause a sharp increase in nitrogen and phosphorus content in water body,which indirectly harms the native ecosystem and oppresses the native near-niche species through physiological stress.Therefore,the bioturbation of native bioturbator may have a certain impact on the invasion of P.canaliculata.However,is the impact of P.canaliculata on the native near-niche species more severe in direct competition and predation,or in indirect effects of its secretion worsening water quality,and how the common local benthic bioturbator affects the invasion of P.canaliculata still unclear.In this study,the native economic species Bellamya purificata,which is close to the niche of the P.canaliculata in the original place was selected as the representative of the native tested snails.Firstly,two sets of experiments were designed,namely,the direct ecological competition and the indirect secretion stress between P.canaliculata and B.purificata.In the direct ecological competition experiment,the two snails directly competed for survival resources;and in the indirect secretion stress experiment,the effects of the two tested snails' secretions on each other were observed.Secondly,in order to simulate the different competition conditions in waterbody in the field,different proportion of individual combinations of the two kinds of snails were set up under two densities(6/12 individuals).On the basis of 12 testing snails that in indirect secretion stress experiment,three sets of experiments were set up to observe the 15-day survival rate,the change rate of body mass and the change rate of single snail body mass of the two kinds of snails in the the co-cultivation system after adding L.hoffmeisteri and the larvae of Chironomus sp.,and observe the effects of different densities and different distribution patterns of L.hoffmeisteri and the larvae of Chironomus sp.on the stress of B.purificata after the invasion of P.canaliculata.Finally,an experiment was designed to imitate the small water bodies with limited resources to observe the competition between P.canaliculata and B.purificata and the influence of benthic animals on this natural competition.The results are as follows:1.No matter which group of experiments,the change rate of body mass and survival rate of P.canaliculata were better than those of B.purificata.The 28-day survival rates of the two kinds of snails were significantly different in the direct competition experiment(P<0.05).In the high-density group of it,the change rate of body mass of B.purificata was significantly worse than that of P.canaliculata if the number of B.purificata was very large(P<0.05),while the survival rate of B.purificata was significantly lower than that of P.canaliculata if the number was small(P<0.05).The change rate of body mass of P.canaliculata was significantly better than that of B.purificata(P<0.01),and the survival rate of P.canaliculata was higher than that of B.purificata(P<0.05)in the indirect endocrine disrupting experiment,in which all the tested B.purificata died when the number of it was too large in the high-density group.The above results fully indicated that the indirect secretion disruption effects of P.canaliculata had a more serious ecological threat than the direct ecological extrusion,which may be an effective life history strategy for P.canaliculata as an invasive species.2.The survial rate of P.canaliculata was significantly higher than that of B.purificata in the absence of bioturbator,but the survival rate of P.canaliculata was significantly reduced(P<0.05)and the survival rate of B.purificata was significantly increased(P<0.05)after adding bioturbators,in which the body mass loss of B.purificata was significantly improved(P<0.05).Regardless of the density of L.hoffmeisteri,the survial rate of P.canaliculata was significantly reduced(P<0.05),and the survial rate of B.purificata was significantly increased(P<0.05),however,this effect was the greatest at high density,which would significantly reduce the survival rate of P.canaliculata(P<0.01).From the distribution of bioturbator in the waterbody,it was the most favorable for the survival of B.purificata when L.hoffmeisteri was evenly distributed.Although the addition of L.hoffmeisteri or the larvae of Chironomus sp.were both beneficial to the survival of B.purificata and weaken the invasive effect of P.canaliculata,the effect of L.hoffmeisteri was better than that of the larvae of Chironomus sp..3.In the extreme competition micro-universe of P.canaliculata and B.purificata,when the available resources in the ecosystem were limited,P.canaliculata would prey on B.purificata.Because of the continuous consumption of water resources,the relationship between them is coexistence of predation and competition.In 12 days of rearing,the survival rate of P.canaliculata was significantly higher than that of B.purificata(P<0.01);at this time,although benthic bioturbator disturbances would also play a certain role,the larvae of Chironomus sp.significantly optimized the relative weight loss rate of B.purificata(P<0.05),while L.hoffmeisteri significantly optimized the relative weight loss rate of B.purificata(P<0.01),but the effect was not as good as a wide open body of water.Conclusion: The indirect secretion interference effect of P.canaliculata to the native species B.purificata was stronger than its direct competition for resources in the ecosystem.,The bioturbation effect of L.hoffmeisteri and the larvae of Chironomus sp.could protect native species and alleviate the endocrine disrupting effect caused by P.canaliculata in large open water bodies,but this treatment method had certain limitations in small enclosed water bodies. |
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