温度和食物水平对海月水母螅状体无性繁殖的影响

The effect of temperature and food supply on the asexual reproduction of moon jelly( Aurelia sp. 1) polyps

水母暴发给近岸人类的生活、渔业资源以及海洋生态系统带来影响。这些近岸海域暴发的水母可以通过有性繁殖和无性繁殖来维持或扩大水母种群数量。在水母生活史中,螅状体的无性繁殖是决定水母体数量的关键阶段,因此对此阶段进行研究。设置了4个温度水平(9、12、15、18℃)、3个食物水平(5个卤虫/螅状体、20个卤虫/螅状体、40个卤虫/螅状体),在12个组合条件下研究温度和食物水平对海月水母螅状体无性繁殖能力和方式的影响。研究结果表明,在海月水母螅状体繁殖子体的各种方式中,匍匐茎生殖是主要的繁殖方式,出芽生殖次之,纵向分裂以及足囊出现几率极低。食物对海月水母螅状体产生总子体数影响显著,温度的影响不显著,食物水平越高,海月水母螅状体繁殖子体的能力越强。食物和温度对螅状体发生横裂均有影响,但温度对螅状体横裂的影响更大。温度对螅状体的横裂率影响显著,食物影响不显著。碟状体的释放发生在12、15、18℃的条件下,温度是影响海月水母螅状体通过横裂生殖释放碟状体数量的最重要因素。可见在螅状体无性繁殖阶段,温度和食物对繁殖方式的影响各不相同。

Jellyfish outbreaks negatively affect humans who live near the coast, and cause harm to fishery resources and marine ecosystems. Jellyfish appearing around the East China Sea maintain or expand their populations by both sexual and asexual reproduction. In the jellyish＇s life cycle, asexual reproduction of polyps is a key stage in determining the number of medusa in the following year; therefore, we focused on this life stage in this study. Previous studies have examined the total number of polyps produced by asexual reproduction under varying environmental conditions, but few studies have examined in detail on the number of new polyps formed via each method of asexual reproduction. Our research aimed to describe the methods of asexual polyp reproduction under different temperatures and food availability levels. In our experiment, following other similar studies we used four temperatures （9, 12, 15, and 18℃ ） and three food amounts （5, 20, and 40 newly-hatched Artemia nauplius per polyp ） in a full-factorial experimental design to observe their effects on the asexual reproduction ability and method of moon jellyfish polyp formation. We systematically recorded the number of new polyps, the method of asexual reproduction, strobilation time, rate of strobilation, and the number of ephyrae released. Stolon formation was the most frequent method of asexual polyp reproduction, followed by direct budding. Longitudinal fission and podocyst methods were rarely observed. Food availability had a significant impact on all of the new moon jellyfish polyps, but the influence of temperature was not significant. Reproduction ability was positively correlated with food availability. Both food and temperature treatments influenced strobilation, and temperature had a greater impact on strobilation than food availability. Temperature significantly increased the incidence of strobilation compared with that of other methods of reproduction, but the effect of food supply was not significant. The rate of strobilation was highest in the moderate temperature group （ 12℃ ）, the 15℃ and 18% groups had lower strobilation rates, and the 9% group had the lowest strobilation rate. Ephyrae were released at the three higher temperatures （ 12℃, 15℃, and 18℃ ）. Temperature was the most important factor influencing the progress of the ephyrae released by strobilation, but food supply also had an important influence. The number of ephyrae released per moon jellyfish polyp in the 12℃ group was the greatest at all three food supply levels （5, 20, and 40 newly-hatched Artemia nauplius per polyp） , while the 9℃ group did not release ephyrae at any food supply level. The greater the availability of food, the more ephyrae were released by the 12℃, 15℃ , and 18℃ groups. At the three highest temperatures, the number of ephyrae released was greatest when 40 newly hatched Anemia nauplius were fed per polyp. Using two-way ANOVA to analyze the influences of temperature and food availability on strobilation and ephyrae release, we conclude that temperature controlled the timing of strobilation, while food amount controlled the number of ephyrae released per polyp. Temperature and food availability have different effects on the asexual methods of jellyfish polyp reproduction.