Institutional Repository of Key Laboratory of Marine Ecology & Environmental Sciences, CAS
|Place of Conferral||中国科学院海洋研究所|
2. 海月水母水螅体胃含物解剖结果表明，水螅体食性广泛，主要由浮游动物碎屑、小型桡足类（平均前体长485 μm）、桡足类幼体及纤毛虫等组成；小型桡足类是胶州湾海月水母水螅体主要的能量来源（碳贡献比例：60.61% ± 18.05%）。水螅体摄食率具有很大的季节波动（0.04-0.372 μg C μg C-1 d-1）。水螅体广布于沿岸生态系统，其数量急剧增多会对浮游-底栖生物耦合产生重要影响。
5. 对2019年5月份在黄海南部、东海北部海域采集的沙海蜇样品，利用胃含物解剖的方法进行食性分析发现，沙海蜇食物类型主要包含小型桡足类（体长< 1000 μm）、大型桡足类（体长> 1000 μm）、桡足类幼体及磷虾类四种；其中小型桡足类（66.1%）与桡足类幼体（32.6%）占据了沙海蜇食物的绝大部分，磷虾数量极少；据此推测，小型桡足类及桡足类幼体应为沙海蜇的主要食物来源。同时本研究评估了该区域沙海蜇的摄食率以及对桡足类的摄食压力，结果表明，2019年5月份在研究海域单位水体沙海蜇的摄食率在9.3-93.3 g C km-2 d-1之间；沙海蜇对调查站位的大型桡足类、小型桡足类及桡足类幼体的平均摄食压力最大分别为0.012%、0.102%、0.081%；据此，本研究认为2019年5月份沙海蜇对黄海南部及东海北部海域桡足类的摄食并不会造成其数量的下降，这主要是由于5月份沙海蜇在该海域处于发生初期，丰度较低、伞径较小，对浮游动物种群产生较低的摄食压力。
6. 三种水母形态结构上的差异决定了捕食机制的不同。海月水母主要通过调整伞径收缩频率来适应不同的饵料环境；而霞水母具有长而密集的触手丝，成为其捕食的有利武器，它主要依靠调整触手丝的伸缩来适应不同的饵料环境，饵料生物对于霞水母伞径收缩频率却没有刺激作用。沙海蜇发育过程中中央口腕愈合，肩板及口腕末端的细小通路成为食物的主要通路；另外，在其伞径下方同样有辐射状食物通路，最终与沙海蜇胃部相通；因此，饵料生物的宽度决定了是否能够被成功捕食；本研究认为，位于沙海蜇肩板及口腕处的食物通路应在2 mm以上。
In recent years, human activities and climate changes have greatly affected the structure and function of marine ecosystem. The number of gelatinous zooplankton especially jellyfish in the marine ecosystem has globally increased. There are many reports about the blooms of jellyfish, and usually the jellyfish blooms caused enormous ecological, economic and societal problems. Jellyfish ecology research has become one of the hot spots in marine ecology. The frequent occurrence of Aurelia coerulea, Nemopilema nomurai, and Cyanea nozakii. blooms in the bay, the offshore and the continental shelf in China have caused serious problems to the tourism, coastal industry and fishery. The vast majority of previous researches have concerned about the life cycle, growth rate and bloom mechanisms of the jellyfish, but the quantitative study on the feeding of these three jellyfish and their trophic relationship with zooplankton and fish populations are relatively scarce in China. Jellyfish are usually considered as voracious predators, which play important roles in the material cycling and energy flow in marine ecosystems. A quantitative study on the diets of these three jellyfish was carried out; their feeding selection and trophic relationship with different prey organisms were analyzed. This research enhanced our understanding to the trophic position and strategy of these three jellyfish in the coastal waters.
In the present study, the three main blooming jellyfish in the Chinese coastal waters A. coerulea, N. nomurai, and C. nozakii were taken as our target species; the main research areas included Jiaozhou Bay, Yellow sea and East China Sea, and the Yangtze estuary, respectively. Feeding activities, gut content analysis, and stable isotope δ13C and δ15N were used to quantitatively investigate the diet model of three species of jellyfish; prey selection and predation mechanisms were analysed simultaneously. Based on these parameters, the effects of jellyfish feeding on marine food web were quantitatively evaluated. The main conclusions of this study are as follows：
1. Clearance rates widely varied with the type of prey organisms. Hydromedusae and fish larvae were captured by A. coerulea and C. nozakii in considerably high efficiency, followed by copepods and chaetognath. Moreover, C. nozakii could greedily prey on A. coerulea. N. nomurai also could efficiently prey on fish larvae, but could bot prey on small medusae, e.g., hydromedusae. Predator size has a significant effect on clearance; clearance rate linearly increased with the cross-sectional area.
2. The diet of A. coerulea polyps was determined using gut content analysis. Digestion time was measured in situ. Ingestion rates, based on gut contents and digestion time, were assessed monthly. A. coerulea polyps had a varied diet, including zooplankton prey detritus, copepods adult and nauplii, and protozoa. Prey detritus represented the bulk of total prey intake in number, followed by copepods, protozoa and nauplii. Copepods (mean body length = 485 μm) accounted for 60.61% ± 18.05% of the carbon ingested by the polyps, while zooplankton prey detritus accounted for 37.75% ± 18.89%. Small copepods should be an important source of nutrition for the polyp stage during jellyfish blooms. Polyps have a large seasonal variation in carbon weight-specific ingestion rates (Iw, range 0.040 to 0.372 μg C μg C-1 d-1). Scyphopolyps are widely distributed predators in littoral ecosystems and may play an important role in plankton-benthos coupling. Massive scyphopolyp blooms may influence pelagic ecosystems.
3. A significant change in stable isotope values was found during C. nozakii growth: δ13C values increased by ~1.93‰, and δ15N values increased by ~2.23‰. The MixSIAR model indicated that C. nozakii underwent a dietary shift during growth, from a seston-based diet in smaller medusae to a zooplankton-based diet in larger medusae. Copepods were an important food source for C. nozakii (31.03%–38.63%) irrespective of size. Gelatinous prey organisms represented 15.74% of the diet of smaller C. nozakii, and 35.18% of the diet of larger C. nozakii, suggesting that larger C. nozakii consumed more gelatinous prey. The diet of C. nozakii included 9.43% N. nomurai and 9.53% small medusae. The results suggested that intraguild predation among these species may be an important trophic relationship in the northern ECS.
4. The population burst of jellyfish Aurelia coerulea occurred in Jiaozhou Bay in 2009, and the potential predation impact of A. coerulea on zooplankton population was investigated. In June and July 2009, the population A. coerulea could potentially clear the volume of water in the Bay more than 0.3 times a day in July. Residence time for copepods was less than 6 d, the minimum residence time was only 2.15 d in June and July. Abundances of copepods, hydromedusae, and chaetognaths were extremely low in 2009 (jellyfish bloom year) as compared to 2008 and 2010 (jellyfish non-bloom years), particularly with respect to the populations of small copepods and hydromedusae. Large predation pressure of A. coerulea occurred to control zooplankton communities in Jiaozhou Bay, at least during June and July. A. coerulea perhaps should be considered as a keystone species in the control of the trophic structure when its massively appears in Jiaozhou Bay.
5. Gut content analysis was used to determine the diet of N. nomurai medusae; 21 N. nomurai individuals (diameter: 5-47 cm) collected in the Yellow Sea and the East China Sea in May 2019 were analysed. Small copepods (body length < 1000 μm), large copepods (body length > 1000 μm), copepods larvae and Euphausiacea were found in the guts of N. nomurai; small copepods (66.1%) and copepods larvae (32.6%) comprised the majority part of the prey in N. nomurai gut. We speculated that small copepods and copepods larvae provided the main energy of N. nomurai growth. The estimated ingestion rate of N. nomurai medusae in unit water in our study area ranged from 9.3 g C km-2 d-1 (the capture rate of the bottom trawl is 1) to 93.3 g C km-2 d-1 (the capture rate of the bottom trawl is 0.1). Basing on the ingestion rate, we estimated the feeding pressure of N. nomurai on the standing stock of copepods (large and small copepods, and copepods larvae). The results indicated that the mean feeding pressure of N. nomurai on standing stock of large copepods, small copepods and copepods larvae were 0.012%, 0.102%, 0.081%, respectively, in May 2019 (the capture rate of the bottom trawl is 0.1). This suggested that the population of N. nomurai have little effect on zooplankton population in May 2019. This was mainly due to the fact that N. nomurai population was in the early stage of its occurrence, with low abundance and small diameter in May 2019.
6. The differences in the morphology and structure of three jellyfish determined the various predation mechanisms. Predation process of A. coerulea based on the fluid motions created during swimming to entrain and capture prey, and we found that swimming propulsion of A. coerulea was adjusted to adapt to different feeding conditions, and swimming speeds of Aurelia and predator-prey encounter rates increase after initial contact with prey. However, C. nozakii medusae had long trailing tentacles, and food was obtained only by random contact with these. The responses of extension and contraction of C. nozakii tentacle were oscillated at different feeding conditions, but no significant difference of swimming propulsion. N. nomurai medusae without central mouths have developed complicated canal systems connecting the tip of tentacle and oral arm to the gut. Prey were gathered by tentacles, and entered into the gut via the canal system at oral arms and scapulets. In addition, there are also radial canal system following the umbrella path, which eventually connect with the gut of jellyfish. Hence, the width of prey determined whether it could be successfully preyed on. In this study, we firstly reported Euphausiacea (body length: 6.1 ± 0.8 mm; width: 2.1 ± 0.3 mm) remained in the medusa scapulet and oral arm, we also confirmed by predation experiments that N. nomurai could successfully capture Euphausiacea. This implied that the diameter of terminal pore is more than 2 mm, which is larger than the previous thought about 1 mm.
Keywords: Jellyfish blooms, Prey selection, Ingestion rate, Gut content analysis, Stable isotope analysis, Feeding pressure
|王朋鹏. 中国近海三种致灾水母的食性及营养关系研究[D]. 中国科学院海洋研究所. 中国科学院大学,2020.|
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