Cell Proliferation in Cubozoan Jellyfish Tripedalia cystophora and Alatina moseri

Cubozoans (box jellyfish) undergo remarkable body reorganization throughout their life cycle when, first, they metamorphose from swimming larvae to sessile polyps, and second, through the metamorphosis from sessile polyps to free swimming medusae. In the latter they develop complex structures like the central nervous system (CNS) and visual organs. In the present study several aspects of cell proliferation at different stages of the life cycle of the box jellyfish Tripedalia cystophora and Alatina moseri have been examined through in vivo labeling of cells in the synthetic phase (S phase) of the cell cycle. Proliferation zones were found in metamorphosing polyps, as well as in juvenile medusae, where both the rhopalia and pedalia have enhanced rates of proliferation. The results also indicate a rather fast cell turnover in the rhopalia including the rhopalial nervous system (RNS). Moreover, T. cystophora showed diurnal pattern of cell proliferation in certain body parts of the medusa, with higher proliferation rates at nighttime. This is true for two areas in close connection with the CNS: the stalk base and the rhopalia.     

Telomerase activity is not related to life history stage in the jellyfish Cassiopea sp.

The polyp (scyphistoma) of the jellyfish Cassiopea sp. can be maintained in culture for a long time, as polyps repeatedly reproduce asexually via formation of vegetative buds or propagules. The medusa, which is the sexually reproducing stage, typically has a relatively short life span. As a first step to understand the difference in life spans of the polyp and medusa stages of Cassiopea sp., we measured telomerase activity in different life cycle stages. We found telomerase activity in tissues of aposymbiotic polyps and propagules and symbiotic ephyrae (newly budded medusae) and adult medusae. No significant difference in telomerase activity was found between polyps and the bell region of the medusae. The cloned elongation products of the stretch PCR contained the TTAGGG repeats suggesting that the jellyfish has the ‘vertebrate’ telomere motif (TTAGGG)_n. This is the first study to show that somatic tissues of both polyp and medusa stages of a cnidarian had telomerase activity. Telomerase activity in somatic tissues may be related to the presence of multipotent interstitial cells and high regenerative capacity of cnidarians.     

Local versus Generalized Phenotypes in Two Sympatric Aurelia Species: Understanding Jellyfish Ecology Using Genetics and Morphometrics

For individuals living in environmentally heterogeneous environments, a key component for adaptation and persistence is the extent of phenotypic differentiation in response to local environmental conditions. In order to determine the extent of environmentally induced morphological variation in a natural population distributed along environmental gradients, it is necessary to account for potential genetic differences contributing to morphological differentiation. In this study, we set out to quantify geographic morphological variation in the moon jellyfish Aurelia exposed at the extremes of a latitudinal environmental gradient in the Gulf of Mexico (GoM). We used morphological data based on 28 characters, and genetic data taken from mitochondrial cytochrome oxidase I (COI) and nuclear internal transcribed spacer 1 (ITS-1). Molecular analyses revealed the presence of two genetically distinct species of Aurelia co-occurring in the GoM: Aurelia sp. 9 and Aurelia c.f. sp. 2, named for its divergence from (for COI) and similarity to (for ITS-1) Aurelia sp. 2 (Brazil). Neither species exhibited significant population genetic structure between the Northern and the Southeastern Gulf of Mexico; however, they differed greatly in the degree of geographic morphological variation. The morphology of Aurelia sp. 9 exhibited ecophenotypic plasticity and varied significantly between locations, while morphology of Aurelia c.f. sp. 2 was geographically invariant (i.e., canalized). The plastic, generalist medusae of Aurelia sp. 9 are likely able to produce environmentally-induced, “optimal” phenotypes that confer high relative fitness in different environments. In contrast, the non-plastic generalist individuals of Aurelia c.f. sp. 2 likely produce environmentally-independent phenotypes that provide the highest fitness across environments. These findings suggest the two Aurelia lineages co-occurring in the GoM were likely exposed to different past environmental conditions (i.e., different selective pressures) and evolved different strategies to cope with environmental variation. This study highlights the importance of using genetics and morphometric data to understand jellyfish ecology, evolution and systematics.     

Polypengeneration und Entwicklungsgeschichte vonEucheilota maculata (Thecata-Leptomedusae)

Polyps and medusae differ in regard to habitats, evolution, and morphological structures. In order to replace the former taxonomic systems which deal with polyp and medusa generations separately, by a single valid classification including both generations, knowledge of all essential life history phases is necessary. Modern methods of culturing marine hydroids are outlined briefly. Successful culturing provides the means to link formerly unidentified polyps or medusae with one another. The present paper is concerned with the hydroidEucheilota maculata Hartlaub, the medusa of which is common in the southern North Sea. The polyps formerly unknown have been reared from fertilized eggs of the medusae. They were raised to full size, formed colonies, and produced gonangia and medusae. Thus the morphology of the single polyp, the polyp colony, and of the young medusa could be investigated in detail. The nematocyst equipment of the two generations and of all developmental stages is described as well as the number of chromosomes. The systematic position of the genusEucheilota is discussed and the diagnosis of the speciesE. maculata, including the two generations, given.     

Comparative phylogeography of meroplanktonic species, <Emphasis Type="Italic">Aurelia</Emphasis> spp. and <Emphasis Type="Italic">Rhizostoma pulmo</Emphasis> (Cnidaria: Scyphozoa) in European Seas

Mass occurrences of scypozoan medusae have become increasingly common in recent decades in European seas, including species in the genera Aurelia and Rhizostoma. We inferred the phylogeographic patterns of metagenetic scyphozoa Aurelia spp. and Rhizostoma pulmo from mitochondrial COI and nuclear ITS regions. No genetic structure was detected in R. pulmo over the Mediterranean Sea. By contrast, the phylogeographic analyses confirmed the separation of Aurelia spp. to several proposed cryptic species. Our results do not support the null hypothesis that both genera have concordant phylogeographic patterns. The resolvable parsimony network of haplotypes was retrieved for Aurelia aurita, Aurelia sp. 5, and Aurelia sp. 8 without connectivity between them and no genetic structure were found within those groups. Even though evidence of hybridization was found between A. aurita and Aurelia sp. 5, that did not break down the phylogenetic separation among them. The lowest haplotype and nucleotide diversity were found in samples of Aurelia sp. 8 and R. pulmo from the northern Adriatic, which acts as a sink area due to strong genetic drift. These new findings will facilitate linking the phenotype of the organism and its ability to survive in a particular environment—which shapes phylogeographic patterns.     

A new Taqman<Superscript>©</Superscript> PCR-based method for the detection and identification of scyphozoan jellyfish polyps

While blooms of large scyphomedusae and cubomedusae receive most public attention owing to effects on tourism (e.g., stinging swimmers), commerce, and fisheries, relatively little attention is given to the inconspicuous benthic polypoid stage. This is particularly troubling when considering the widespread translocation of some invasive marine jellyfish. The transport of benthic polyps (via ships, barges, and offshore drilling platforms) is theorized to be the most likely way in which invasive jellies are globally transported. Yet given the extremely small size and cryptic nature of most benthic polyps, identifying and tracking them in the field amongst the larger communities of fouling organisms is extremely difficult. To this end, we have developed a rapid molecular assay for detecting benthic jellyfish polyps from three scyphozoan genera in the Gulf of Mexico. One of these (Phyllorhiza spp.) is an invasive scyphozoan established in the Gulf of Mexico and is theorized to have been spread worldwide as a fouling organism on the hulls of cargo ships, while the other two (U.S. Chrysaora sp. and Gulf of Mexico Aurelia spp.) are local blooming animals that have shown recent numerical increases in the Gulf of Mexico. This method involves a multiplex Real-Time Polymerase Chain Reaction (PCR) assay using Taqman^© probes that can be run on DNA extracted from whole-community scrapings of benthic surfaces, such as boat hulls, dock pilings, oilrigs, and settling plates. Specificity tests indicated that all Taqman^© probes were successful against all individuals of target taxa, but not against 17 non-target local and worldwide scyphozoan and hydrozoan species. Tests showed all probes to be extremely sensitive, reacting to as few as 50 copies of template DNA, with one (Chrysaora sp.) reacting to as few as 10 copies. The assay correctly identified individual polyps of Aurelia sp. and Chrysaora sp. The use of this Taqman^© assay on tissue collected from whole benthic scrapings should allow screening of incoming ships to the Gulf of Mexico for the invasive P. punctata, and locating and studying the cryptic benthic stages of northern Gulf of Mexico jellyfish, which will lead to a better understanding of the overall population distribution and bloom dynamics of medusae.     

The life cycle of Chrysaora lactea Eschscholtz, 1829 (Cnidaria,Scyphozoa) with notes on the scyphistoma stage of three other species

The life cycle of Chrysaora lactea Eschscholtz, 1829, a common species on the Brazilian coast, is described. Mature medusae were collected and isolated in a planktonkreisel, whereupon planulae appeared after 1–2 days. These planulae settled and metamorphosed into polyps. Fully developed scyphistomae typically possessed 16 tentacles, and on strobilation produced from 2 to 10 ephyrae. The ephyrae were transparent and had characteristic nematocyst warts on the exumbrella. Tentacles first appeared near the margin on the subumbrella. Ephyrae and young medusae were maintained in laboratory conditions up to 7 months.     

Predation potential of the jellyfish Drymonema larsoni Bayha & Dawson (Scyphozoa: Drymonematidae) on the moon jellyfish Aurelia sp. in the northern Gulf of Mexico

The jellyfish Drymonema larsoni bloomed in the northern Gulf of Mexico in the Fall of 2000 and fed voraciously on the moon jellyfish Aurelia sp., especially where they were concentrated in frontal convergence. We evaluated the predation potential of D. larsoni on Aurelia sp. medusa using laboratory and field data. Our data set represents the most complete study to date on the new scyphozoan family Drymonematidae and indicates that D. larsoni may be one of the most effective predators on other jellyfish recorded to date. On average, each D. larsoni medusa contained 2.7 Aurelia sp. prey, but as many as 34. In addition, 94% of moon jellyfish unassociated with D. larsoni showed scarring from previous contact with D. larsoni tentacles. Digestion times for D. larsoni feeding on individual Aurelia sp. ranged from 2 to 3 h and averaged 2.7 h. Potential clearance rates for predation on Aurelia sp. were extremely high (320–1043.5 m³ d⁻¹) and indicate that D. larsoni is potentially an important predator on Aurelia sp. blooms where the species co-occur. When the two species co-occur in numbers, predation by D. larsoni medusae could reduce moon jellyfish blooms, possibly alleviating predation pressure on lower trophic levels utilized by Aurelia sp., such as copepods and the early life history stages of ecologically and economically important fish and invertebrate species.     

Green Fluorescence of Cytaeis Hydroids Living in Association with Nassarius Gastropods in the Red Sea

Green Fluorescent Proteins (GFPs) have been reported from a wide diversity of medusae, but only a few observations of green fluorescence have been reported for hydroid colonies. In this study, we report on fluorescence displayed by hydroid polyps of the genus Cytaeis Eschscholtz, 1829 (Hydrozoa: Anthoathecata: Filifera) found at night time in the southern Red Sea (Saudi Arabia) living on shells of the gastropod Nassarius margaritifer (Dunker, 1847) (Neogastropoda: Buccinoidea: Nassariidae). We examined the fluorescence of these polyps and compare with previously reported data. Intensive green fluorescence with a spectral peak at 518 nm was detected in the hypostome of the Cytaeis polyps, unlike in previous reports that reported fluorescence either in the basal parts of polyps or in other locations on hydroid colonies. These results suggest that fluorescence may be widespread not only in medusae, but also in polyps, and also suggests that the patterns of fluorescence localization can vary in closely related species. The fluorescence of polyps may be potentially useful for field identification of cryptic species and study of geographical distributions of such hydroids and their hosts.     

Acoustic survey of a jellyfish-dominated ecosystem (Mljet Island,Croatia)

Acoustic techniques have been proposed as a new tool to assess jellyfish populations. However, the presence of mixed echoes from jellyfish and other organisms that share their distribution often prevent accurate estimates of their abundance and distribution being obtained. The isolated population of Aurelia inhabiting the Veliko Jezero (Big Lake-BL) of Mljet Island, in the South Adriatic Sea, offered a good opportunity to employ acoustic techniques to assess an entire jellyfish population. During October 2–5, 2006, combined video and acoustic methods were used in BL to determine the vertical distribution of medusae. Two synoptic acoustic surveys were performed during the day and night. In the daylight echograms, medusae were clearly discernible from the acoustic data, and their presence verified by video camera images, as forming a layer of varying density at and below the thermocline (15–30 m). The depth of the jellyfish layer also coincided with the depth of maximum dissolved oxygen concentration. The echointegration of these daylight data enabled quantification the Aurelia population, at a frequency of 120 kHz. In the night echograms, the acoustic signals of Aurelia were at least partially masked by pelagic and demersal fish, which disaggregated from schools and formed a layer associated with a strong thermocline at 15 m. An average target strength (TS) of −76.4 dB was obtained in situ corresponding to a mean length of 10.8 cm and a mean wet weight of 134 g measured from sampled medusae. These results were combined with echo-integration values to provide an estimate of 4,238,602 individuals and a biomass of 568 tons of Aurelia in BL. This study provided a synoptic view of Mljet Lake and illustrated the potential of acoustic surveys of jellyfish populations to contribute to ecosystems studies. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

Seasonality in Polyps of a Tropical Cubozoan: A latina nr mordens

A latina nr mordens have been located in large predictable spawning aggregations near Osprey Reef in the Coral Sea eight to ten days after a full moon; however, polyps have never been located in-situ. The polyp stage contributes to the abundance of medusae through asexual reproduction and metamorphosis, and may influence the periodicity of medusae by metamorphosis of the polyp. To elucidate the relationship between medusae periodicity and polyp ecology, polyps were exposed to thermal and osmotic treatments in order to determine the theoretical environmental limits to their distribution. Maximum fecundity occurred in thermal treatments of 21 to 25ºC and the theoretical minimum thermal requirement for population stability was approximately 17ºC. Polyps were also exposed to five feeding regimes and fecundity was found to be positively correlated with feeding frequency. Thermal and osmotic variations did not induce metamorphosis in this species, however, reduced food did. The implications of asexual reproduction and cues for metamorphosis in relation to population dynamics of this species are discussed.     

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.     

Release and growth of Cyanea capillata (L.) ephyrae in the Gullmar Fjord,western Sweden

In an investigation carried out in the Gullmar Fjord, western Sweden, the autecology of the scyphozoans Aurelia aurita (L.) and Cyanea capillata (L.), has been studied. This paper focuses on results concerning C. capillata, but comparisons with Aurelia aurita are made and discussed. The main period of strobilation was in winter and early spring. The extent of ephyrae release was only one tenth of that of A. aurita. The period of rapid growth of ephyrae and medusae during the spring was delayed one month compared to the pattern for Aurelia. The Cyanea scyphistomae are exposed to predation by the nudibranch Coryphella verrucosa and only very limited settling of Cyanea planulae occurred in the area. Immigration from the North Sea is probably a major factor regulating the appearance of Cyanea capillata along the western coast of Sweden.     

Biomass and size structure of the scyphomedusa Aurelia aurita in the northwestern Black Sea during spring and summer

The abundance, biomass and size structure of the scyphomedusa,Aurelia aurita, was measured during two research cruises tothe northwestern Black Sea (July–August 1995 and April–May1997). Average biomass of Aurelia was relatively constant (132–179g wwt m^–2) throughout the investigation period and similarto previous years. Abundance and biomass at individual stationsappeared to be unrelated to temperature and salinity when thelatter exceeded ~13. Biomass was low at coastal stations inthe plume of the Danube where depth was <20 m and salinitydropped to <11. The spring cruise (April–May) coincidedwith, or just followed the peak of strobilation. The summercruise (July–August) took place near the beginning ofplanulae larvae release. The population size structure was dominatedby small individuals in spring, while large medusae prevailedmainly in late summer. Aurelia was, on average, larger at deepwater stations during summer, suggesting that per capita foodsupply was higher further offshore. The individual body massincreased from spring through summer. Accordingly, the volume(wet wt) to length (bell diameter) relation changed significantly.If all medusae measured throughout the seasons were pooled,volume (V, in cm³) was related to length (L, in cm) accordingto V = 0.08 L^2.71, which is similar to measurements conductedin other coastal areas. In contrast to the common conjecture,we did not find inverse relations between biomasses of Aureliaand the combjelly Mnemiopsis leidyi. Preliminary feeding experimentsindicate that Aurelia may feed upon small Mnemiopsis. The significanceof indirect trophic relations and direct feeding interactionsamong the gelatinous zooplankton in the Black Sea has importantconsequences for the energy flow along the food web and, therefore,needs further study.     

A silent invasion

Invasions mediated by humans have been reported from around the world, and ships’ ballast water has been recognized as the main source of marine invaders worldwide. Some invasions have dramatic economic and ecological consequences. On the other hand, many invasions especially in the marine realm, can go unnoticed. Here we identify a human mediated, worldwide introduction of the hydrozoan species Turritopsis dohrnii. The normal life cycle of hydrozoans involves the asexual budding of medusae from colonial polyps. Medusae of Turritopsis, however, when starved or damaged, are able to revert their life cycle, going back to the polyp stage through a process called transdifferentiation. They can thus easily survive through long journeys in cargo ships and ballast waters. We have identified a clade of the mitochondrial 16S gene in Turritopsis which contains individuals collected from Japan, the Pacific and Atlantic coasts of Panama, Florida, Spain, and Italy differing from each other in only an average of 0.31% of their base-pairs. Fifteen individuals from Japan, Atlantic Panama, Spain, and Italy shared the same haplotype. Turritopsis dohrnii medusae, despite the lack of genetic differences, are morphologically different between the tropical and temperate locations we sampled, attesting to a process of phenotypic response to local conditions that contributes to making this grand scale invasion a silent one.     

Genetic characterization of the scyphozoan jellyfish Aurelia spp. in Chinese coastal waters using mitochondrial markers

Blooms of the moon jellyfish Aurelia spp. have occurred in the harbors and coastal waters around the world. The phylogenetic relationship and genetic characterization of Aurelia spp. was determined along the Chinese coastal waters based on sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene. The molecular analysis confirmed that all samples collected in Chinese coastal waters were Aurelia sp.1. We also analyzed the phylogenetic and population genetic structure of Aurelia sp.1 using the newly generated sequences supplemented with existing data from previous studies. The phylogenetic analyses of the COI regions did not support geographically restricted groups among the global samples of Aurelia sp.1. Analysis of molecular variance (AMOVA) indicated a complex genetic population structure and pattern of connectivity. Populations of Aurelia sp.1 were highly structured between most sampling sites over distances as small as 100 km (Rizhao and Qingdao) in certain cases. However, non-significant pairwise F_ST values were also observed between short geographic distances (Yantai, Rongcheng and Qingdao) and relatively distant sampling sites (Caofeidian, Rizhao and Japan). The life-cycle characteristics, together with the prevailing ocean currents in this region and possible anthropogenic introduction, were proposed and discussed as the main factors that determined the genetic patterns of Aurelia sp.1.     

Cell adhesion to extracellular matrix is different in marine hydrozoans compared with vertebrates

Extracellular matrices (ECMs) of phylogenetically very distant organisms were tested for their ability to support cell adhesion, spreading and DNA replication in reciprocal xenograft adhesion tests. Mechanically dissociated cells of the medusa Podocoryne carnea (Cnidaria, Hydrozoa) were seeded on ECMs of polyps and medusa, and on several ECM glycoproteins or entire ECMs from vertebrates. In reciprocal experiments, cells from different vertebrate cell-lines were seeded on ECMs of polyps, medusae and also on electrophoresed and blotted extracts of both types of ECMs. The results demonstrate that medusa cells adhere and spread on polyp and medusa ECMs but do not recognize vertebrate ECMs or purified ECM glycoproteins. Vertebrate cells in contrast adhere, spread and proliferate on ECMs of polyps and medusae. The number of attached cells depends on the cell type, the type of ECM and, in certain cases, on the stage of the cell cycle. Cell adhesion experiments with pretreated ECMs of polyps and medusae, e.g. oxidation of carbohydrate residues with sodium-metaperiodate, or blocking of certain carbohydrate moieties with the lectin wheat germ agglutinin or a carbohydrate-specific monoclonal antibody, demonstrate that ECM carbohydrates are more important for cell-ECM interactions of medusa cells than for vertebrate cells. Furthermore, the experiments indicate that polyp and medusa ECMs contain different components which strongly modulate adhesion, spreading and DNA replication of vertebrate cells.