北京两个水库的桃花水母及其发生条件初探

Species identification and preliminary study on the driving factors to freshwater jellyfish(Craspedacusta)occurrence in two reservoirs,Beijing

为鉴定北京怀柔水库和黄松峪水库发生的桃花水母并检验其水环境质量相关性,对2022年9月9日和10日采自2个水库的桃花水母进行形态学和遗传结构分析,并结合常规水生态监测数据,初步探究桃花水母发生的水环境条件。结果显示,怀柔水库和黄松峪水库桃花水母形态结构较为相似,依据其伞径、触手数目、主辐触手长于其它触手、管状平衡囊数、刺丝囊疣圆锥状环状排列及囊状性腺等形态特征初步鉴定为索氏桃花水母和嘉定桃花水母。ITS序列分析结果显示怀柔水库样本与索氏桃花水母遗传相似性100%,黄松峪水库样本与嘉定桃花水母遗传相似性100%,佐证了形态学鉴定结果。2个水库桃花水母发生前后库区pH、溶解氧、总氮和总磷浓度以及生化需氧量等因子无明显差异,而水温和食源浮游动物生物量变动明显,水质处于中营养-轻度富营养状态。9月上旬,2个水库水温快速下降到25℃以下,而适口食源浮游动物生物量增长至1.2 mg/L以上。推断:1)桃花水母环境耐受力较强,偏爱食物丰富的中营养水体;2)水温骤变(骤升或骤降)和适口食物充裕可能是刺激桃花水母启动有性生殖的重要生态因子。据此分析了温变胁迫和营养限制对桃花水母发生的可能驱动效应,以期为桃花水母发生机理的研究提供参考。

To identify the species of freshwater jellyfishes(Craspedacusta)occurred in Huangsongyu Reservoir and Huairou Reservoir of Beijing and to explore their water quality-indicating practicability,we analyzed the morphological and genetic features of the jellyfishes sampled from the two reservoirs on September 9 and 10,2022,respectively.Combined with the data of physio-chemical factors and zooplankton biomass from routine aquatic ecosystem monitoring,we explored the conditions for the occurrence of jellyfishes.The results showed that the morphological characteristics of Craspedacusta samples from Huairou Reservoir and Huangsongyu Reservoir were very similar,with the mean umbrella diameters of(15.8±3.1)and(13.2±1.9)mm,(342±48)and(268±3.4)tentacles,and(140±27)and(134±2)statocysts,respectively.Four main tentacles were obviously longer than others,with trochiformis nematocyst warts arranged annularly on them.Meaningfully,their gonads were different in shape and color.Huairou specimen had large white cystiform gonads,and Huangsongyu specimen had smaller gonads in grey.These morphological characteristics confirmed the jellyfishes in Huairou Reservoir and Huangsongyu Reservoir were C.sowerbyi and C.kiatingi,respectively.ITS base sequence was amplified and sequenced by PCR and DNA sequencing,then finally compared with other Craspedacustas sequences in GenBank,which resulted in 100%genetic similarities between the Huairou samples and C.sowerbyi,and between the Huangsongyu samples and C.kiatingi and thus well verified the morphological identification results.In detecting the driving factors to the appearance of jellyfish medusa,seasonal variations of zooplankton biomass and six physiochemical factors were analyzed for checking the sudden changes just before and/or after the medusa occurrence in both reservoirs.Results showed that the pH,dissolved oxygen,total nitrogen and phosphorus concentrations,and biochemical oxygen demand kept relatively stable through the summer-autumn months without observable variation in both reservoirs,indicating a mesotrophic to mildly eutrophic state.In early September when jellyfish appeared,surface water temperature continued declining to lower than 25℃,and the biomass of zooplankton continued increasing to higher than 1.2 mg/L.Rich food might meet the energy needs of jellyfish for sexual reproduction,and temperature declining might have functioned as the driving factor.We concluded that Craspedacusta are highly tolerant to eutrophication and have a preference for mesotrophic waters,and that sudden changes of water temperature(sudden rise or fall)and abundance of palatable food are important factors that stimulate the sexual reproduction of jellyfishes.Accordingly,the driving effects of temperature shock stress and nutrient limitation were analyzed,with a view to providing a reference for the mechanism study of freshwater jellyfish occurrence in future.