Effects Of Global Warming On Snails In Shallow Lakes: An Outdoor Experimental Mesocosms

In recent decades global warming has been the focus of many studies on climate change, but few studies have examined the interaction of global warming and other factors on the population dynamic of benthic animal in lakes.Therefore, we performed a mesocosm of two years experiment which simulated shallow lakes temperature elevation in the middle and lower reaches of the Yangtze River in 2100 to monitor the snail population dynamics. The experiment in 2014 was designed four treatments as follows, C treatment which was ambient temperature, T treatment which was increased by 4.5°C based on ambient temperature, P treatment which was added 50 μg/L phosphorus and ambient temperature, TP treatment which was added 50 μg/L phosphorus and heating temperature. The aim of this experiment was to discuss the interaction of warming and eutrophication on the population dynamics and community structure of snails and established a method to explore the effects of temperature elevating on morphology of Bellamya aeruginosa. The experiment in 2015 was also setup four treatments, and the designs of C and T treatments were the same as 2014, F treatment which was added a 60 g Cyprinus carpio and ambient temperature, TF treatment which was added a 60 g Cyprinus carpio and heating temperature. The experiment explored the interaction of warming and food chain length on snail population dynamics. Results of these studies as follows:(1) To explore the effects of temperature elevation on morphology of Bellamya aeruginosa. Snail shell dimensions(area, perimeter, height and width) were easily quantifiable of morphological traits by geometric morphometric, and made a linear model regression with weight, respectively. Then analysis of covariance was applied to contrast the difference of regression equations between the two treatments and we recognized that the perimeter was statistically significantly different when the temperature elevated. Meanwhile, higher temperature increased the individuals of recruitment in spring. The effects of temperature elevation on morphology of Bellamya aeruginosa were reflected in the following three aspects. The density of Bellamya aeruginosa was significantly increased in heating tanks, and induced small juvenile shell size after maturation as a result of more intense intraspecific competition. Elevated temperature led to different food quality in the diet of Bellamya aeruginosa, morphological variation was indirectly effected in the process of growth due to different qualities of food. When the water temperature got warm, the change of pH value generated limited calcium availability and constrained calcification within the shell simultaneously which influenced the shell formation and induced shell plasticity consequently.(2) During the experiment in 2014, five species including Bellamya aeruginosa, Radix swinhoei, Alocinma longicornis, Parafossarulus striatulus and Gyraulus convexiusculus were sampled. The dominant species were Bellamya aeruginosa and Alocinma longicornis in C treatment, Bellamya aeruginosa and Radix swinhoei in T treatment, Bellamya aeruginosa, Radix swinhoei, Parafossarulus striatulus in P treatment and Bellamya aeruginosa, Radix swinhoei in TP treatment. In the experiment, it could not be found a pronounced effect of warming on biomass or density of Bellamya aeruginosa, Radix swinhoei and Parafossarulus striatulus. However, phosphorus addition had a far greater impact than warming on biomass and density of these populations. Higher nutrient concentrations resulted in a greater biomass and density of Radix swinhoei and Parafossarulus striatulus but the density or biomass of Bellamya aeruginosa was not significantly affected. Interaction of warming and nutrients addition exhibited complex mechanisms on the snail community. Bellamya aeruginosa and Alocinma longicornis showed significant decrease in their biomass and density, but that of Radix swinhoei and Parafossarulus striatulus were higher when warming and nutrient enrichment acted in combination. This study showed that synergitic of warming and eutrophication may change the population structure and biomass of snails, which resulted in changing of lake ecosystem structure and function.(3) In the experiment of 2015, Bellamya aeruginosa and Radix swinhoei were sampled. Bellamya aeruginosa was dominant species and Radix swinhoei was subdominant species in each treatment. Warming significantly increased the abundance and biomass of leaf-floating macrophyte, but diminished the biomass of phytoplankton and submerged macrophyte because of continually shading effects by leaf-floating macrophyte. As a result, less food resource were applied to gastropod. Therefore, biomass and density of Bellamya aeruginosa and Radix swinhoei showed significant decrease due to warming. In F treatment, Bellamya aeruginosa and Radix swinhoei, especially sexually immature individuals declined through direct predation effects by Cyprinus carpio and the growth of these two populations were also indirectly influenced by increased turbidity due to Cyprinus carpio bioturbation. In TF treatment food chain length increasing had a far greater impact than warming through predation and bioturbation effects on biomass and density of the snail populations. As the temperature elevated, food consumption and bioturbation of Cyprinus carpio enhanced in TF treatment to induce higher water turbidity than F treatment. Accordingly, TF treatment produced a more profound impact on the biomass and density of Bellamya aeruginosa, Radix swinhoei than T or F treatment. Overall, benthic fish should be taken more seriously in the management of shallow freshwaters, which may contributed to stabilization of structure and function of lake ecosystems.