Size-based Prey Selectivity and Dietary Shifts in the Jellyfish, Aurelia aurita

Gut content analyses on field-caught Aurelia aurita showed bothquantitative and qualitative change in diet as a function ofmedusa size. Larger medusae tended towards greater numbersand diversity of prey (up to 1550 individual prey representingas many as 13 different prey groups). We also found that medusasize was a good predictor of prey diversity recovered from themedusa gut. While a shift toward greater prey diversity inlarger medusae might be explained by increased contact rateswith 'rare' prey taxa, we also found size-based prey selectivitychanges in A. aurita. We used in situ gut content data to describeselectivity by A. aurita for three prey types representing varyingdegrees of swimming or escape velocity. Fish eggs were usedas a non-swiming prey, and small (     

Induction of segmentation in polyps of Aurelia aurita (Scyphozoa, Cnidaria) into medusae and formation of mirror-image medusa anlagen

Polyps of Aurelia aurita can transform into several medusae (jellyfish) in a process of sequential subdivision. During this transformation, two processes take place which are well known to play a key role in the formation of various higher metazoa: segmentation and metamorphosis. In order to compare these processes in bilaterians and cnidarians we studied the control and the kinetics of these processes in Aurelia aurita. Segmentation and metamorphosis visibly start at the polyp's head and proceed down the body column but do not reach the basal disc. The small piece of polyp which remains will develop into a new polyp. The commitment to the medusa stage moves down the body column and precedes the visible onset of segmentation by about one day. Segmentation and metamorphosis can start at the cut surface of transversely cut body columns, leading to a mirror-image pattern of sequentially developing medusae.     

Protein composition of mesoglea and mesogloeal cells of medusa Aurelia aurita

Protein composition of mesoglea of the scyphomedusa Aurelia aurita was revealed in SDS-PAGE. Some major bands are visible in mesoglea of a mature medusa: 30, 45-47, 85 kDa, three bands between 100-200 kDa, and several bands with molecular weights > 300 kDa. Polyclonal antisera RA45/47 against protein 45 kDa were raised. RA45/47 react with 45-47 kDa protein in mesogleal sample and protein 120 kDa in mesogleal cells on immunoblot. Immunohistochemical analysis of A. aurita histological sections of young and mature medusae showed antigen localization in mesogleal cell granules and in the apical part of ectodermal cells. In mature medusae, the antigen was localized also in elastic fibers. We can conclude that in A. aurita mesogleal cells, along with ectodermal cells, take part in the formation of extracellular matrix of mesoglea.     

Development time of planula larvae on the oral arms of the scyphomedusa Aurelia aurita

The development time from zygote to late stage of planula larvaeon the oral arms of Aurelia aurita was found to be 270 and 170h at 12 and 22°C, respectively. The mean ratio of the diameterof the long axis to the short axis in newly released planulaewas 2.27.     

Molecular characterization of aspartylglucosaminidase,a lysosomal hydrolase upregulated during strobilation in the moon jellyfish,Aurelia aurita

The life cycle of the moon jellyfish, Aurelia aurita, alternates between a benthic asexual polyp stage and a planktonic sexual medusa (jellyfish) stage. Transition from polyp to medusa is called strobilation. To investigate the molecular mechanisms of strobilation, we screened for genes that are upregulated during strobilation using the differential display method and we identified aspartylglucosaminidase (AGA), which encodes a lysosomal hydrolase. Similar to AGAs from other species, Aurelia AGA possessed an N-terminal signal peptide and potential N-glycosylation sites. The genomic region of Aurelia AGA was approximately 9.8 kb in length and contained 12 exons and 11 introns. Quantitative RT-PCR analysis revealed that AGA expression increased during strobilation, and was then decreased in medusae. To inhibit AGA function, we administered the lysosomal acidification inhibitors, chloroquine or bafilomycin A1, to animals during strobilation. Both inhibitors disturbed medusa morphogenesis at the oral end, suggesting involvement of lysosomal hydrolases in strobilation.     

A newly discovered oxidant defence system and its involvement in the development of Aurelia aurita (Scyphozoa, Cnidaria): reactive oxygen species and elemental iodine control medusa formation

In Aurelia aurita, applied iodine induces medusa formation (strobilation). This process also occurs when the temperature is lowered. This was found to increase oxidative stress resulting in an increased production of iodine from iodide. One polyp produces several medusae (initially termed ephyrae) starting at the polyp's oral end. The spreading of strobilation down the body column is controlled by a feedback loop: ephyra anlagen decrease the tyrosine content in adjacent polyp tissue by producing melanin from tyrosine. Endogenous tyrosine is able to remove iodine by forming iodiferous tyrosine compounds. The reduced level of tyrosine causes the ephyra-polyp-border to move towards the basal end of the former polyp. We argue that an oxidant defence system may exist which makes use of iodide and tyrosine. Like other marine invertebrates, polyps of Aurelia contain iodide ions. Inevitably produced peroxides oxidise iodide into iodine. The danger to be harmed by iodine is strongly decreased by endogenous tyrosine which reacts with iodine to form iodiferous tyrosine compounds including thyroxin. Both substances together, iodide and tyrosine, form an efficient oxidant defence system which shields the tissue against damage by reactive oxygen species. In the course of evolution (from a species at the basis of the animal kingdom like Aurelia to a highly evolved species like man) the waste product thyroxin (indicating a high metabolic rate) has developed into a hormone which controls the metabolic rate.     

Field observations of four Aurelia labiata jellyfish behaviours: swimming down in response to low salinity pre-empted swimming up in response to touch,but animal and plant materials were captured equally

Jellyfish live in complex environments and must continually make behavioural choices. In field observations, adult Aurelia labiata were confronted with a conflict between swimming up elicited by touch of the manubrium and swimming down elicited by low salinity. Following a touch, downward-swimming medusae (1.5–2.0 m deep) turned and swam to within 0.5 m of the surface when the salinity in the top 1.5 m of the water column was greater than 20 ppt but medusae uniformly refused to swim up into the top 1.25 m when the salinity was less than 20 ppt even after being touched three times. The central nervous system of A. labiata appears to have neural circuitry that specifies their response when medusae encounter stimuli that elicit incompatible behaviours. Upward-swimming adult medusae had animal, vegetable or cellulose (paper) material dispersed ahead of them. Medusae captured each material on the bell margin and transported it to a gastric pouch. Medusae displayed only minor behavioural differences in the process. Having sensory, neural and muscular systems organized to capture and pass to the stomach, a huge variety of materials allows medusae to survive in different seasons and environments.     

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.     

Evolution and taxonomy in capitate hydroids and medusae (Cnidaria: Hydrozoa)

A cladistic analysis of Capitata groups the families in four suborders based on medusa characters (such as manubrium morphology, position of gonads, and position and number of marginal tentacles) and hydroid characters (such as presence or absence of an oral tentacle whorl, and the different development of the tentacles of the oral and aboral whorls). On the family and generic levels, the revision results in changes which unite the separate hydroid and medusa taxonomic systems, defining genera which are not based on characters solely relating to the reduction of medusae to fixed gonophores. In those families where the reduction of the medusa can be analysed, it is shown that the reduction occurred after all synapomorphies defining the genera had evolved and usually affected individual species within a genus rather than the original species from which the other species in the genus evolved. This supports the view that medusa reduction is not in itself a valid generic character. A discussion of the theories of 'inconsistent' or 'mosaic' evolution concludes that no difference in evolutionary rate or degree of specialization can be demonstrated among taxa with free medusae and taxa with gonophores.     

Evolutionary origin of rhopalia: insights from cellular‐level analyses of Otx and POU expression patterns in the developing rhopalial nervous system

SUMMARY In Cnidaria, the medusae of Scyphozoa and its sister‐group Cubozoa uniquely possess rhopalia at their bell margin. These sensory centers coordinate behavior and development. We used fluorescent in situ hybridization and confocal microscopy to examine mRNA expression patterns in Aurelia sp.1 (Cnidaria, Scyphozoa) during early medusa formation, while simultaneously visualizing the developing nervous system by immunofluorescence. The genes investigated include AurOtx1, and the POU genes, AurPit1, and AurBrn3, homologs of genes known to function in cephalar neural organization and sensory cell differentiation across Bilateria. Our results show that AurOtx1 expression defines the major part of the oral neuroectodermal domain of the rhopalium, within which distinct populations of AurBrn3‐ and AurPit1‐expressing sensory cells develop. Thus, despite the unique attributes of rhopalial evolution, we suggest that the rhopalial nervous system of scyphozoan medusae involves similar patterns of differential expression of genes that function in bilaterian cephalic structure and neuroendocrine system development. We propose that rhopalia evolved from preexisting sensory structures that developed distinct populations of sensory cells differentially expressing POU genes within Otx oral‐neuroectodermal domains. This implies some commonality of developmental genetic functions involving these genes in the still poorly constrained common ancestor of bilaterians and cnidarians.     

Central neural circuitry in the jellyfish Aglantha: a model 'simple nervous system'

Like other hydrozoan medusae, Aglantha lacks a brain, but the two marginal nerve rings function together as a central nervous system. Twelve neuronal and two excitable epithelial conduction systems are described and their interactions summarized. Aglantha differs from most medusae in having giant axons. It can swim and contract its tentacles in two distinct ways (escape and slow). Escape responses are mediated primarily by giant axons but conventional interneurons are also involved in transmission of information within the nerve rings during one form of escape behavior. Surprisingly, giant axons provide the motor pathway to the swim muscles in both escape and slow swimming. This is possible because these axons can conduct calcium spikes as well as sodium spikes and do so on an either/or basis without overlap. The synaptic and ionic bases for these responses are reviewed. During feeding, the manubrium performs highly accurate flexions to points at the margin. At the same time, the oral lips flare open. The directional flexions are conducted by FMRFamide immunoreactive nerves, the lip flaring by an excitable epithelium lining the radial canals. Inhibition of swimming during feeding is due to impulses propagated centrifugally in the same epithelium. Aglantha probably evolved from an ancestor possessing a relatively simple wiring plan, as seen in other hydromedusae. Acquisition of giant axons resulted in considerable modification of this basic plan, and required novel solutions to the problems of integrating escape with non-escape circuitry.     

Population dynamics of the scyphomedusa Aurelia aurita in Southampton Water

The population dynamics of the scyphomedusa Aurelia aurita inSouthampton Water is characterized. Strobilation, indicatedby the presence of 1 mm ephyrae, occurred from the end of Januaryto the middle of March. Maximum abundances of up to 8.71 m^–3occurred soon after ephyrae release, after which numbers declinedsteadily until the end of June, when the population was absentfrom Southampton Water. The residence time of 3–4 monthsis somewhat less than that reported in many other areas, includingKiel Bight and Gullmarfjord. The carbon biomass of A.auritaaccounted for 92–97% of the predominant gelatinous biomass(A.aurita, Pleurobrachia pileus and Phialidium hemisphericum)in the upper estuary, and this reached a maximum of 30.2 mgC m^–3 in May 1990 and 27.6 mg C m^–3 in June 1991.Coincident with increased water temperature and mesozooplanktonabundance during May, growth rates increased from 0.02–0.30mm day^–1 to a peak of 4.8 mm day^–1, with a maximumbell diameter of 120–140 mm reached in late May/earlyJune. Size to maturity was variable, although the smallest medusaobserved to be ‘ripe’, i.e. containing dividingeggs and planula larvae in the brood sacs on the oral arms,were 64–71 mm. Aurelia aurita is believed to be endemicto Southampton Water, but because of the double high water inthe area, short flushing rates of between 4.5 and 20 days maybe responsible for such short residence times of Aurelia medusae.The effects of strong NE winds were considered as factors governingthe distribution of medusae in years of atypical temporal abundance.     

中国东南沿海裸鞘花水母一新属及三新种记述

记述了采自中国东南沿海台湾海峡南部、福建南部东山湾和福建东部宁德三都湾裸鞘花水母1新属——拟长管水母属Dipurenella gen.nov.和3新种,即刺胞海帽水母Halitiara knides sp.nov.,东山拟长管水母Dipurenella dongshanensis sp.nov.和粗管外肋水母Ectopleura crassocanalis sp.nov.。详细描述其形态特征,并与近似种进行比较。模式标本保存于厦门大学海洋与环境学院。     

海月水母生长规律及水管系统发育研究

本文对烟台海域海月水母水母体阶段伞径、腕长及体重的生长规律进行了研究,并首次对其生长过程中水管系统的发育进行了观察。结果表明,在人工培养条件下,海月水母体重(W)与伞径(D:15~150㎜)呈幂函数增长;腕长(L)与伞径(D)呈线性关系;伞径生长曲线方程为：Dt = 4×10-6t4-0.0014t3 0.1087t2 0.5079t 9.428 (R2=0.9993)。。海月水母初生碟状体出现主辐管与间辐管,3日龄时碟状体出现从辐管,11日龄时出现环管、分离点。随着水母的生长,伞径增大,水管系统的分离点数与聚合点数逐渐增多,成熟时1/4伞部分离点数最多为66个,聚合点数最多为32个。     

Temperature effects on asexual reproduction rates of scyphozoan species from the northwest Mediterranean Sea

In recent decades, many areas worldwide have experienced mass occurrences of jellyfish. To determine how temperature may affect jellyfish populations in the northwest (NW) Mediterranean Sea, we maintained polyps of three scyphozoan species, Aurelia aurita, Rhizostoma pulmo, and Cotylorhiza tuberculata in the laboratory at three temperatures (14, 21, 28°C) to test effects on survival and production of new polyps and ephyrae. Temperature significantly affected survival of all species, with longest survival of A. aurita and R. pulmo at 14°C and of C. tuberculata at 21°C. More polyps were budded by all species at temperatures above 14°C. A. aurita produced the most buds polyp⁻¹ (43.5) and R. pulmo the fewest (8.8). Strobilation occurred only at 14°C for A. aurita and at 21°C for C. tuberculata. For R. pulmo, fewer polyps strobilated and strobilated later at 14°C. These patterns of survival and asexual reproduction were seasonally appropriate for each species in the NW Mediterranean, where A. aurita medusae occur earliest (~April–May) in cool waters, followed by R. pulmo during May–June, and then by C. tuberculata in mid-summer. Comparisons among scyphozoan species suggested that many may be restricted by low temperatures, and that global warming may benefit temperate species, but not tropical or boreal species.     

Carbon content of the neritic scyphomedusa Chrysaora fuscescens

An analysis of the role of scyphomedusae in a planktonic ecosystemrequires that biomass or numerical abundance estimates be convertibleinto standard units for comparison with other components ofthe planktonic community. One species under investigation isthe brown sea nettle, Chrysaora fuscescens, which is very abundantin coastal waters of the west coast of North America (Shenker,1984). For this species, the carbon content of whole immatureanimals and the body components of sexually mature medusae weredetermined. Immature medusae contained a mean carbon content0.202% of the wet weight. The bell, oral arms and gonadal tissueof mature medusae had mean carbon levels 0.156, 0.554 and 0.576%of the wet weight, respectively. When the relative proportionsof these body tissues were calculated, the mean carbon contentof whole mature medusae was determined to be 0.280% of the wetweight.     

A biomimetic robotic jellyfish (Robojelly) actuated by shape memory alloy composite actuators

An analysis is conducted on the design, fabrication and performance of an underwater vehicle mimicking the propulsion mechanism and physical appearance of a medusa (jellyfish). The robotic jellyfish called Robojelly mimics the morphology and kinematics of the Aurelia aurita species. Robojelly actuates using bio-inspired shape memory alloy composite actuators. A systematic fabrication technique was developed to replicate the essential structural features of A. aurita. Robojelly's body was fabricated from RTV silicone having a total mass of 242 g and bell diameter of 164 mm. Robojelly was able to generate enough thrust in static water conditions to propel itself and achieve a proficiency of 0.19 s(-1) while the A. aurita achieves a proficiency of around 0.25 s(-1). A thrust analysis based on empirical measurements for a natural jellyfish was used to compare the performance of the different robotic configurations. The configuration with best performance was a Robojelly with segmented bell and a passive flap structure. Robojelly was found to consume an average power on the order of 17 W with the actuators not having fully reached a thermal steady state.     

Differential gene expression in the jellyfish Aurelia aurita

The body of Aurelia aurita, as well as other diploblasts, consists of two epithelial layers: ectodermal and gastral epithelium. These two tissues are separated by mesoglea, or extracellular matrix. In most coelenterates mesoglea is acellular. In A. aurita mesogleal cells are scattered in mesoglea. Differential display PCR was used to compare mRNA pools from ectodermal epithelium, gastral epithelium and mesoglea. 4 novel gene fragments were cloned and sequenced. According to RTPCR results, one of these fragments is differentially expressed in the ectodermal epithelium.     

Behavioural response of the scyphozoan jellyfish Aurelia aurita (L.) upon contact with the predatory jellyfish Cyanea capillata (L.)

Underwater manipulative experiments were carried out in situ to investigate the sensibility of the jellyfish Amelia aurita (L.) to contact with the tentacles of Cyanea capillata (L), commonly known as a predator on A. aurita. Movements of individual medusae touched by tentacles of C. capillata and other objects were video‐recorded during SCUBA dives. The behavioural variable studied was change in swim pulse frequency. The results showed that A. aurita was highly susceptible to the tentacles of C. capillata and responded with an increased swim pulse frequency when touched at the umbrellar margin but not at the central exumbrella. Contact with other objects also induced a behavioural response in A. aurita.