温度对海月水母螅状体生长及繁殖的影响

Effects of temperature on the growth and asexual reproduction of moon jellyfish (Aurelia coerulea) polyps

采用了实验生态学方法,研究温度对海月水母螅状体生长及繁殖的影响。实验设6个温度梯度(12, 15, 18, 21, 24, 27℃),共持续56d。测定了螅状体的柄径生长,繁殖数量;观察了螅状体的无性繁殖方式;分析了温度影响下的螅状体的能量分配及繁殖策略。结果表明,温度显著影响螅状体的生长及繁殖,在较高温度组,匍匐茎生殖是螅状体无性繁殖的主要方式,随着温度降低,出芽生殖比例增加。较高温度组螅状体繁殖速率较快,新生螅状体个体较小,分布较分散;而较低温度组,新生螅状体个体较大,数量较少,均较紧密的分布在亲代螅状体周围。在培养56d的周期内,除27℃处理组外,其他各处理组螅状体柄径均有所增加,但其增加的速率随着温度的升高而降低。而27℃处理组,螅状体整体状态不好,基本不摄食,培养35d时全部死亡。综上,较低温度条件下,螅状体倾向于选择增加自身个体大小以应对不良环境,而当环境条件适宜时,螅状体倾向于选择通过无性繁殖产生更多子代的方式以扩大种群数量。温度显著影响螅状体的繁殖策略,进而显著影响螅状体的种群数量。

Jellyfish outbreaks have become increasingly, and caused harm to marine ecosystems. Massive aggregations of Aurelia coerulea have occurred in Bohai Sea and Yellow Sea, China since the end of the 20 th century. Their blooms have caused serious impact on the structure of fishery resources, and biological and ecological studies were to be undertaken to countermeasure their blooms. Research on jellyfish blooms has concentrated on the ephyrae and adult medusae. More recently, people recognized that it was necessary to examine the benthic stages. In the jellyfish′s life cycle, asexual reproduction of polyp is a key stage in determining the number of medusa in the following year;therefore, we focused on the life stage in this study. Environmental factors such as temperature affect the growth and rate of asexual reproduction of jellyfish at the polyp stage. Much less work has been done on the modes of asexual reproduction of polyps, the way of energy distribution, and the reproductive strategy in different environments. The growth, survival and asexual reproduction of moon jellyfish(Aurelia coerulea) polyp were investigated at six temperatures(12, 15, 18, 21, 24, 27 ℃) in the laboratory experiment, which lasted for 56 days. We systematically recorded the survival and growth of polyps, the number of new polyps, and the method of asexual reproduction every week. The results showed that the mortality rate of polyps was 0%, except for the polyps maintained in 27 ℃, in which the mortality rate of polyps exceeded 60% in 14 days, and all polyps were dead in 42 days. Aurelia coerulea has shown a great variety of asexual reproduction modes in the experiment including production of stolons and hence new polyps, direct budding of new polyps, longitudinal fission, and formation and excystment of cysts, and the temperature have affected the asexual reproduction. The polyps produced the new individuals mainly using formation of stolon in higher temperature and budding in lower temperature. Growth of individuals(calyx diameter) significantly increased with temperature decreased. The calyx diameter of polyp increased by 157% in 12 ℃, 168% in 15 ℃,127% in 18 ℃, 67% in 21 ℃, and 40% in 24 ℃. But the number of new polyps significantly increased with temperature increased. However, polyps at the lowest temperature had a higher percentage of larger individuals and slower population growth rate than those at warmer temperatures. These results suggest that the reproductive strategy to maximize production of Aurelia coerulea is to increase the size of polyps colonies by asexual budding when conditions are good(warmer temperatures and abundant food generally during spring and summer). Budding activity slows, but the size of polyps increases, during the colder winter period leading up to strobilation, resulting in the production of a greater number of ephyrae. It is concluded that the polyps of Aurelia coerulea can tolerate wide temperature variations. The colony of polyps can continue to grow and survive through a broad range of conditions spanning many seasons, thus ensuring survival of the population.