不同初始螺类密度对沉水植物刺苦草Vallisneria spinulosa Yan及其附着藻类的影响

Effects of different initial snail densities on submersed macrophyte Vallisneria spinulosa Yan and its epiphyton

大型水生植物及其附着藻类是浅水湖泊中的重要初级生产者。淡水螺类作为重要的初级消费者,其密度对沉水植物及其附着藻类的影响存在争议。本研究设置4种初始螺类密度(0、40、80、240 ind·m-2),研究淡水螺类(椭圆萝卜螺Radix swinhoei H.Adams)对刺苦草(Vallisneria spinulosa Yan)及其附着藻类的直接牧食作用和螺类种群的变化。结果显示,在添加螺处理中,刺苦草和人工基质表面附着藻类的生物量显著降低,同时沉水植物的生长显著增加,在较高初始密度螺类处理中刺苦草产生更多的分株。到实验结束时,螺类的死亡率较高,但3个有螺处理间螺类鲜重无显著差异,而高初始密度螺类条件下的最终密度仍较高,同时个体重量(均重)也较小。在中富营养条件下淡水螺类可以直接牧食沉水植物叶片,但对植物生长的抑制作用不显著,有可能是因为沉水植物并不能作为唯一的食物来源维持螺类种群,同时螺类的种群结构受到水体营养水平等因素的制约。

Macrophytes and their epiphyton are the main primary producers in shallow lakes. Freshwater snails are the main primary consumers in freshwater ecosystems, but it is still debatable whether snail densities are an important factor that determine the growth of macrophytes and their epiphyton. We established four snail densities （0, 40, 80, and 240 ind·m^-2） to investigate the grazing impact of snails （Radix swinhoei H. Adams） on the submerged macrophyte Vallisneria spinulosa Yan and its epiphyton, and determine the dynamics of the snail populations from the interaction. Results indicated that R. swinhoei strongly reduced the biomass of the epiphyton, but promoted the biomass of the macrophytes, and at the highest initial snail density even induced higher ramet number of macrophytes. The direct grazing effects of snails on macrophytes were observed but were not significant at the moderate eutrophic level, probably because submerged macrophytes alone could not support the high densities of snails. The size structure of the snail population could quickly respond to nutrient levels of the water-bodies and food resources in the environment.