Induction of stolon settlement in the scyphopolyps ofAurelia aurita (Cnidaria,Scyphozoa, Semaeostomeae) by glycolipids of marine bacteria

The settlement of pedal stolons of scyphopolyps ofAurelia aurita Lamarck could be induced by addition of a species of bacteria from the family Micrococcaceae. After treatment of the bacteria with several organic solvents a crude lipid extract free of bacteria could be obtained which was shown to be effective in inducing stolon settlement. Crude lipids extracted from the late logarithmic growth phase had an optimal effect on stolon attachment, in contrast to previously published experiments showing that all logarithmic phases of bacteria had the same level of effectiveness. After separation of the crude lipid extracts by thin layer chromatography and subsequent bioassay of the reeluated substances, acylgalactosidyldiglyceride and monogalactosidyldiglyceride were identified as the effective substances. Monogalactosidyldiglyceride was only found in bacteria from the medium logarithmic growth phase, whereas the former was found at all stages. The effectiveness of acylgalactosidyldiglyceride was independent of the growth phase of the extracted bacteria.     

Dissociation and reaggregation of cells of Chrysaora quinquecirrha (Cnidaria, Scyphozoa)

Cells of scyphistomae, strobilae, and ephyrae were dissociated with trypsin and reaggregated. Clumping was inhibited in low Ca++ and by puromycin, but not by collagenase or sugars. Reaggregates from the oral end of the polyp developed tentacles and mouths first and basal structures later, whereas the opposite sequence occurred with cells from the lower gastric region. Nile-blue-stained cells from hypostome or peduncle did not form specific structures in the reconstructed polyp, but were distributed throughout the animal. Ephyra cell aggregates showed little morphogenesis, whereas cells from presumptive ephyra tissue gave rise to structures with tentacles and multiple oral openings. Mixed reaggregates containing equal proportions of polyp and ephyra cells formed irregular structures with transparent outer layer and opaque inner cell mass, suggesting stage-specific sorting.     

Bacterially induced stolon settlement in the scyphopolyp ofAurelia aurita (Cnidaria,Scyphozoa)

Unsettled stoloniferous scyphopolyps ofAurelia aurita Lamarck were offered different substrates for settlement under defined conditions. On addition of different biogenic and abiotic substrates, a pure strain of bacteria, a species of Micrococcaceae, was observed to trigger the settlement of the stolon. The settlement reaction only takes place following direct contact with the bacteria; sterile filtrated culture medium of the same bacterial strain was not able to induce settlement. The bacteria were found to be effective on stolon settlement during the logarithmic growth phase, but not during the stationary phase.     

In situ time budgets of the scyphomedusae Aurelia aurita, Cyanea sp., and Chrysaora quinquecirrha

The in situ behavior of three scyphomedusan species was videorecorded by scuba divers in natural daytime lighting with minimalinterference to the medusae. The mean percentage of time thatindividual medusae spent swimming ranged from 93 to 100%. Therewere no significant differences in the percent time spent swimmingbetween life stages of a species (ephyra, adult) or betweenspecies. The predominance of swimming activity by medusae indicatesthat swimming, and hence the creation of fluid motions responsiblefor prey entrainment and capture, plays a widespread functionalrole in feeding by scyphomedusae.     

D-Methionine and gold chloride alleviate adverse effects of glutamate on motility of ephyrae of Aurelia aurita (Linnaeus, 1758) (Scyphozoa: Semaeostomeae)

Glutamate (MSG) causes low pulse numbers and swimming cessation in Aurelia jellyfish ephyrae. Ephyrae given MSG for 1h and subsequently maintained in artificial sea water (ASW) were observed at 1, 3, 24, and 48 h intervals. Abnormality of motility was found at all post-treatment periods but some ephyrae resumed swimming and normal pulsing within 48 h. Swimming and pulsing were impaired in a significant number of ephyrae within 15 min of MSG treatment. The mechanism of MSG action on ephyrae motility is unknown, but glutamate damage to neurons and hair cells of higher animals is partly attributed to the formation of reactive oxygen species (ROS). Laser confocal fluorescent microscopy of ephyrae following MSG treatment indicated an increase of calcium and free radicals in the ephyrae as early as 5 min following MSG exposure. To determine whether antioxidants could alleviate MSG effects, we exposed ephyrae to gold chloride before, during, and after treatment with MSG. Ephyrae given gold chloride pre-treatment for 1h and then transferred into gold chloride plus MSG for 1h showed statistically significant recovery from MSG impairment of pulsing at the 3, 24, and 48 h post-glutamate time periods and higher numbers of swimmers at 3 h and 24 h. Ephyrae groups given gold plus MSG but without gold pretreatment showed recovery of swimming at 24 h and pulsing at 48 h. d-methionine given simultaneously with MSG significantly improved the pulse numbers and swimming of ephyrae at the 3, 24, and 48h post-glutamate time periods compared to those receiving MSG alone. Both d-methionine and gold chloride accelerated the time of recovery from glutamate-induced motility impairment, possibly through their antioxidant activities.     

Isolation,characterization, and comparison of hemolytic peptides in nematocyst venoms of two species of jellyfish (Chrysaora quinquecirrha and Cyanea capillata)

• 1.1. Hemolysins of the sea nettle, Chrysaora quinquecirrha, and the lions' mane jellyfish, Cyanea capillata, collected in the Delaware Bay were partially purified by sequential gel-filtration and high performance liquid chromatography.
• 2.2. The nematocyst contents of both jellyfish had hemolytically active fractions containing large quantities of glycine and serine along with an unknown amino acid residue.
• 3.3. The Chrysaora hemolysin appeared to have a mol. wt greater than 6000 but less than 10,000 daltons.
• 4.4. Glycophorins were the most effective inhibitors to the hemolysins at the lowest concentration.

     

On some features of embryonic development and metamorphosis of Aurelia aurita (Cnidaria, Scyphozoa)

Aurelia aurita is a cosmopolite species of scyphomedusae. Its anatomy and life cycle are well investigated. This work provides a detailed study on development and structure of A. aurita planula before and during its metamorphosis. Intravital observations and histology study during the settlement and metamorphosis of the planulae demonstrated that the inner manubrium lining of primary polyp (gastroderm) develops from the ectoderm of the planula posterior end. The spatial and temporal dynamics of serotonergic cells from the early embryonic stages until the formation of the primary polyp were studied for the first time. In addition, the distribution of tyrosinated tubulin and neuropeptide RF-amide at different stages of A. aurita development was traced.     

Limitations on the Use of Impermeable Mesocosms for Ecological Experiments Involving Aurelia sp. (Scyphozoa: Semaeostomeae)

Microcosms permit controlled ecological experiments but theeffects of small enclosures on predators, prey, and their interactions,compromise their relevance to field populations. I examinedthe effects of Aurelia size on the utility of impermeable mesocosmsdeployed in highly stable water columns. Aurelia of all sizes(5-29 cm bell diameter) were observed adhered to walls. Individualslarger than 10 cm adhered to walls in disproportionately highnumbers, experienced a significant decline in mean size, andincurred physical damage at greater rates, than those less than10 cm. These results demonstrate that, at least for impermeablewalled mesocosms deployed in low turbulence environments, largerenclosures will not necessarily (i) ameliorate wall effectsfor animals of the size typically manipulated in microcosmsand (ii) make enclosures suitable for manipulating Aurelia largerthan those normally enclosed in microcosms. The mechanism proposedto explain adhesion suggests that enclosure walls alter thehydrodynamics of fluid flow around Aurelia, which may have implicationsfor estimating the predation impact of these animals since thehydrodynamics of feeding and swimming have co-evolved.     

On natural metamorphosis inducers of the cnidarians Hydractinia echinata (Hydrozoa) and Aurelia aurita (Scyphozoa)

 Hydractinia echinata and Aurelia aurita produce motile larvae which undergo metamorphosis to sessile polyps when induced by external cues. The polyps are found at restricted sites, A. aurita predominantly on rocks close to the shore, H. echinata on shells inhabited by hermit crabs. It has been argued that the differential distribution of the polyps in their natural environment largely reflects the distribution of the natural metamorphosis-inducing cues. In the case of H. echinata, bacteria of the genus Alteromonas were argued to meet these conditions. We found that almost all substrates collected in the littoral to induce metamorphosis in H. echinata, and several bacterial strains isolated from the sea, including the common E. coli, induce metamorphosis efficiently. In A. aurita metamorphosis may be induced by the water–air interface, whereby metamorphosis precedes (final) settlement. Received: 7 December 1998 / Accepted: 8 July 1999     

Effects of low dissolved oxygen on survival and asexual reproduction of scyphozoan polyps (Chrysaora quinquecirrha)

Hypoxic conditions are common in many coastal environments such as Chesapeake Bay. While medusae appear to be quite tolerant of low dissolved oxygen (DO) concentrations, the effects of hypoxia on the benthic polyp stages are unknown. Chrysaora quinquecirrha (DeSor) polyps, and were subjected to 5 DO treatments (air-saturated [control], 3.5, 2.5, 1.5 and 0.5 mg l^–1) in the laboratory. Polyp survival and development were documented over 24 d. Virtually no mortality occurred in any treatment during the first 5 d. Total polyp mortality after 24 d was 59.3% at the lowest DO concentration, whereas <3% mortality was observed in the air-saturated treatment. Formation of stolons and strobilae occurred in all treatments, however, the proportions of polyps undergoing stolonation and strobilation were significantly greater in all DO concentrations above 0.5 mg l^–1. Polyp encystment was not observed in any treatment over the course of the 24 d experiment. These results indicate that polyps can survive and asexually propagate even during prolonged exposure to hypoxic conditions.     

Metabolism of 131I in relation to strobilation of Aurelia aurita L. (Scyphozoa)

The ¹³¹I isotope of iodine has been used to follow the uptake and metabolism of iodine during the process of strobilation in pre-conditioned polyps of Aurelia aurita L. Strobilating polyps accumulated free iodide from the media against a concentration gradient, the segmented portion of the polyps accumulating about three times as much as the basal portion. Almost all of the accumulated iodide appeared in the soluble portion of an acid-ethanol extract of polyp tissue as inorganic iodide. The time course of accumulation of iodine was not affected by previous exposure to either higher temperature or iodide. Inorganic iodide rather than organically bound iodine is thought to be the effective factor in the initiation of strobilation.     

Physiological and chemical analysis of neurotransmitter candidates at a fast excitatory synapse in the jellyfish Cyanea capillata (Cnidaria, Scyphozoa)

Motor nerve net (MNN) neurons in the jellyfish Cyanea capillata communicate with one another by way of fast, bidirectional excitatory chemical synapses. As is the case with almost all identified chemical synapses in cnidarians, the identity of the neurotransmitter at these synapses is unclear. MNN neurons are large enough for stable intracellular recordings. This, together with the fact that they can be exposed, providing unlimited access to them and to their synapses, prompted a study of the action of a variety of neurotransmitter candidates, including those typically associated with fast synapses in higher animals. Only the amino acids taurine and β-alanine produced physiological responses consistent with those of the normal EPSP in these cells. Moreover, chemical analysis revealed that both taurine and β-alanine are present in the neurons and released by depolarization. These various findings strongly suggest that either or both of these amino acids, or a closely related compound is the neurotransmitter at the fast chemical synapses between MNN neurons.     

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.