Food and feeding of Aurelia aurita in Tokyo Bay with an analysis of stomach contents and a measurement of digestion times

In situ seasonal variations in stomach contents of Aurelia aurita (L.) in Tokyo Bay, Japan, were analyzed. Copepods, such as Oithona davisae Ferrari & Orsi were the predominant food items of A. aurita from June to November. The mean digestion time measured in incubation experiments was 0.95 h. Daily rations calculated using stomach content data and digestion times were 2.2–21.8 mg C ind^–1 corresponding to 0.58–5.56% of body carbon. The ingestion rate increased significantly with an increase in medusa size, although no significant relationship was found between medusa size and carbon specific daily ration. The zooplankton community in Tokyo Bay is characterized by the significant dominance of O. davisae and it is assumed that the prosperity of A. aurita is caused by the high abundance of the O. davisae population. It is suggested that a food chain comprised of microflagellates, cyclopoid copepods O. davisae, and A. aurita is the most significant one in Tokyo Bay and only a small portion of production is transferred to fish.     

Plate in the zone of oocyte and germinal epithelium contact in Scyphomedusa Aurelia aurita binds antibodies to ZP-domain protein mesoglein

The morphological features of oocyte and germinal epithelium (epithelial wall of germinal sinus) contact area in Scyphomedusa Aurelia aurita are described. Growing oocytes were divided into seven stages based on oocyte size. The structure revealed the area of contact between the oocyte and the germinal epithelium called the contact plate. During oocyte growth, single granules are fused into the homogeneous mass area of oocyte contact with epithelium. Plate components bound antibodies to mesoglein. It was assumed that the plate material contained ZP-domain proteins. Electrophoresis and immunoblotting results show that proteins immunologically similar to mesoglein have higher molecular masses, probably due to post-translation modifications, which are common for extracellular proteins. On the other hand, however, gonad proteins may be other representatives of jellyfish ZP-domain proteins. Further experiments should be conducted to clarify which alternative is true.     

温度和食物水平对海月水母螅状体无性繁殖的影响

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。     

Aurelin, a novel antimicrobial peptide from jellyfish Aurelia aurita with structural features of defensins and channel-blocking toxins

A novel 40-residue antimicrobial peptide, aurelin, exhibiting activity against Gram-positive and Gram-negative bacteria, was purified from the mesoglea of a scyphoid jellyfish Aurelia aurita by preparative gel electrophoresis and RP-HPLC. Molecular mass (4296.95 Da) and complete amino acid sequence of aurelin (AACSDRAHGHICESFKSFCKDSGRNGVKLRANCKKTCGLC) were determined. Aurelin has six cysteines forming three disulfide bonds. The total RNA was isolated from the jellyfish mesoglea, RT-PCR and cloning were performed, and cDNA was sequenced. A 84-residue preproaurelin contains a putative signal peptide (22 amino acids) and a propiece of the same size (22 amino acids). Aurelin has no structural homology with any previously identified antimicrobial peptides but reveals partial similarity both with defensins and K+ channel-blocking toxins of sea anemones and belongs to ShKT domain family.     

温度对海月水母螅状体生长及繁殖的影响

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。     

温度、盐度对海月水母碟状体生长及存活的影响

海月水母为我国近海主要大型灾害水母种类之一,当自然环境适宜其生长与繁殖时,易出现暴发性的增殖现象,严重破坏了我国近岸海洋生态系统的稳点与平衡。采用实验生态学方法,研究了温度(2.5、5、7.5、10、15、20、25、27.5、30℃)和盐度(15、20、25、30、35、40)对海月水母碟状体存活与生长的影响,实验共进行30d。结果显示,在实验设置的温盐范围内,温度、盐度均显著影响碟状体的存活与生长。在盐度15-35条件下,海月水母碟状体可以在温度2.5-25℃存活,在15-25℃范围内可正常生长;在温度20-25℃和盐度20-30条件下适宜海月水母碟状体生长,其中温度20℃和盐度25条件下海月水母碟状体特定生长率达到最大。与盐度相比,温度对碟状体的影响较大,在盐度15-35条件下,随着温度的升高,碟状体的伞径逐渐增大,其碟状体形态向水母体形态的转变速度加快。在达到临界点25℃时,若继续升高温度,碟状体的生存率与生长率显著下降。温度与盐度对海月水母碟状体的生存与生长具有明显的交互效应,碟状体在实验过程中表现出在较低温度条件下提高了对较高盐度的适应性。研究表明,温度、盐度的变化显著影响碟状体的生长与存活,直接导致碟状体种群数量变动,进而影响成熟水母体种群数量。结论为进一步探索大型水母暴发的生态环境机理提供重要科学依据。     

Reproduction and life history strategies of the common jellyfish, Aurelia aurita, in relation to its ambient environment

The scyphozoan Aurelia aurita (Linnaeus) is a cosmopolitan species, having been reported from a variety of coastal and shelf sea environments around the world. It has been extensively studied over the last 100 years or so, and examination of the literature reveals three striking features: (1) the presence of populations in a wide range of environmental conditions; (2) large inter-population differences in abundance and life history patterns over large and small spatial scales; and (3) inter-annual variability in various aspects of its population dynamics. A. aurita is clearly a highly flexible species that can adapt to a wide range of environmental conditions. While various physiological and behavioural characteristics explain how A. aurita populations can take advantage of their surrounding environment, they do not explain what governs the observed temporal and spatial patterns of abundance, and the longevity or lifespan of populations. Understanding these features is necessary to predict how bloom populations might form. In a given habitat, the distribution and abundance of benthic marine invertebrates have been found to be maintained by four factors: larval recruitment (sexual reproduction), migration, mortality and asexual reproduction. The aims of this review are to determine the role of reproduction and life history strategies of the benthic and pelagic phases of A. aurita in governing populations of medusae, with special attention given to the dynamic interaction between A. aurita and its surrounding physical and biological environment.     

A method for in situ estimation of prey selectivity and predation rate in large plankton, exemplified with the jellyfish Aurelia aurita (L.)

A method to estimate predation rates of large predatory zooplankton, such as jellyfish and ctenophores, is outlined. Large plankton size allows direct visual tracking of the predator during the process of foraging. The presented method is novel in the sense that it measures predation rate of a specific individual plankton predator in situ.After prey has been evacuated from the gut of an individual predator, the predator is incubated in situ, and observed by SCUBA-divers who recapture the individual after a defined time. Given that this incubation time is shorter than prey digestion time, predation rate can be calculated as increase in gut content over time. Clearance rates for different prey can be calculated from predation rates and prey concentrations in the water, allowing accurate estimates of prey selectivity. Thus, the problem of unknown feeding history and feeding environment, which can otherwise be a problem in prey selectivity studies of in situ-captured predators, is circumvented. Benefits and limitations of the method are discussed.The method was applied to adult medusae of the common jellyfish Aurelia aurita. A large variation in number of captured prey was detected both among individual jellyfish and among the various oral arms and gastric pouches within individuals. Clearance rates varied strongly with prey type. The medusae selected large crustacean prey (cladocerans and copepods/copepodites) over echinoderm larvae and copepod nauplii. Prey distribution within the medusae indicates that both tentacles and oral arms were used as prey capturing sites. Food passage time from prey capturing organs to gastric pouches was estimated.