Asexual reproduction in scyphistomae of Aurelia sp.: Effects of temperature and salinity in an experimental study

The growth and survival of colonies and individuals within sedentary polyp colonies of moon jellyfish (Aurelia sp.) was investigated at three temperatures and three salinities in laboratory experiments. Growth rates of colonies (number of polyps and number of buds in the colony) and individuals (number of buds per active scyphistomae) significantly increased with temperature, but were not affected by salinity. Survival was high in all treatment combinations indicating a wide tolerance to environmental conditions. However, scyphistomae at the lowest temperature had a greater percentage of larger individuals and slower population growth rate than those at warmer temperatures. These results suggest that the reproductive strategy to maximise production of Aurelia sp. is to increase the size of scyphistomae colonies by asexual budding when conditions are good (warmer temperatures and abundant food generally during spring and summer). Budding activity slows, but the size of scyphistomae increases, during the colder winter period leading up to strobilation, resulting in the production of a greater number of ephyrae. The trigger for strobilation is possibly stressful conditions. However, if trigger conditions do not occur, the colony of scyphistomae can continue to grow and survive through a broad range of conditions spanning many seasons, thus ensuring survival of the population.     

Effects of pH on asexual reproduction and statolith formation of the scyphozoan, <Emphasis Type="Italic">Aurelia labiata</Emphasis>

Although anthropogenic influences such as global warming, overfishing, and eutrophication may contribute to jellyfish blooms, little is known about the effects of ocean acidification on jellyfish. Most medusae form statoliths of calcium sulfate hemihydrate that are components of their balance organs (statocysts). This study was designed to test the effects of pH (7.9, within the average current range, 7.5, expected by 2100, and 7.2, expected by 2300) combined with two temperatures (9 and 15°C) on asexual reproduction and statolith formation of the moon jellyfish, Aurelia labiata. Polyp survival was 100% after 122 d in seawater in all six temperature and pH combinations. Because few polyps at 9°C strobilated, and temperature effects on budding were consistent with published results, we did not analyze data from those three treatments further. At 15°C, there were no significant effects of pH on the numbers of ephyrae or buds produced per polyp or on the numbers of statoliths per statocyst; however, statolith size was significantly smaller in ephyrae released from polyps reared at low pH. Our results indicate that A. labiata polyps are quite tolerant of low pH, surviving and reproducing asexually even at the lowest tested pH; however, the effects of small statoliths on ephyra fitness are unknown. Future research on the behavior of ephyrae with small statoliths would further our understanding of how ocean acidification may affect jellyfish survival in nature.     

盐度对不同温度下海月水母螅状体存活和无性繁殖的影响

海月水母是全球近岸海域的主要致灾水母种类之一,其螅状体的繁殖情况与种群数量是影响水母暴发的重要因素.采用实验生态学的方法分别研究了高温(21 ℃)和低温(12 ℃)条件下,不同盐度梯度对螅状体存活与无性繁殖的影响.结果表明: 高温条件下,盐度15～40时螅状体存活率均大于90%,适合出芽生殖盐度范围为20～32,其中28为最适盐度;在低盐(≤15)或高盐(≥36)环境下,螅状体会进行足囊生殖以度过不良环境条件. 低温条件下,20～40盐度组螅状体存活率均大于90%,20～32盐度组适于螅状体出芽生殖,其中28盐度组出芽生殖效率最高;20～40盐度适于横裂生殖,其中28～32盐度组最利于螅状体横裂生殖. 说明海月水母螅状体有较强的盐度耐受性,一定范围内盐度对螅状体无性生殖影响不显著.     

Effects of climate warming on strobilation and ephyra production of North Sea scyphozoan jellyfish

Recent studies have correlated fluctuations in jellyfish abundances with climatic changes, leading to speculation that the warming trend in the North Sea will affect the strobilation activity of Scyphozoa. The present study provides long-term data (10–22 months) on temperature effects on the species Aurelia aurita, Cyanea capillata, Cyanea lamarckii and Chrysaora hysoscella. Strobilation at current winter temperature (5°C) in the German Bight was compared to strobilation at warmer winter temperatures. Simulated winter temperature of 10°C had several positive effects on strobilation, as compared to 5°C: 1. A longer strobilation period or higher ephyra production per polyp in A. aurita, C. lamarckii and Ch. hysoscella; 2. Higher percentages of polyps strobilating in A. aurita and Ch. hysoscella; 3. More ephyrae per strobila in C. capillata and C. lamarckii; 4. A shorter strobilation duration in C. capillata and C. lamarckii. Cold winter temperatures of 5°C promoted strobilation in C. capillata, but inhibited strobilation in A. aurita and reduced ephyra production in C. lamarckii and Ch. hysoscella. These results suggest that climate warming will benefit A. aurita, but not cold-water C. capillata. The distributions of C. lamarckii and Ch. hysoscella probably could expand to the north.     

大型水母幼体生长的影响因子研究进展

21世纪以来,中国东、黄海,韩国西海岸以及日本海连年发生大型水母暴发现象,对海洋渔业的生产活动以及海洋生态系统带来巨大的影响。水母暴发形成机制非常复杂,解释其发生机理并有效预报是目前急待解决的问题。大型水母的生活史中有明显的世代交替现象,受精卵,浮浪幼虫,螅状体,足囊,横裂体到碟状体的幼体发育阶段属无性世代,幼蜇发育到成蜇阶段属有性世代。在早期生活史中,螅状体的足囊繁殖与横裂生殖是大型水母无性繁殖的重要方式,对其成体的数量形成至关重要。综述了国内外有关温度、盐度、光以及营养条件对大型水母早期发育阶段的影响研究进展,研究表明温度是影响螅状体发育以及足囊繁殖和横裂生殖的最主要的环境因子;盐度、光和营养条件在适温范围内,均对螅状体和横裂生殖有一定的影响,其上下限随水母种类和发育阶段有所变化。展望了大型水母早期幼体研究的发展趋势,如环境因子对不同种类的大型水母幼体生长机理的影响、多个环境因子对幼体的综合作用、动态的环境因子与大型水母幼体之间的关系等。     

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.     

水母旺发的诱因及对海洋环境的影响

水母旺发已成为一种新型海洋生态灾害,使海洋生态系统的结构和功能、海洋生态环境受到严重破坏.本文总结了水母旺发的可能诱因,重点探讨了水母旺发对海水生源要素、溶解氧、酸碱度以及生物群落的影响.结果表明: 水母旺发与其自身生理结构与生活史密切相关,其具有的身体结构简单、生长迅速、繁殖性强、世代间隔时间短及耐不良环境等特点,使其遇合适环境可迅速繁殖.水母旺发的主要直接诱因可能与海水温度变化有关,海水升温可导致水母食物增多,促进水母生殖,尤其对暖温性水母,更易引起水母聚集繁殖,形成旺发.富营养化、气候变化、过渡捕捞、生物入侵、栖息地改变也是水母旺发的重要影响因素.水母旺发可显著影响生源要素的形态和生物地球化学循环,水母排放NH₄⁺和PO₄^3-速率分别为59.1～91.5 μmol N·kg^-1·h^-1和1.1～1.8 μmol P·kg^-1·h^-1,可为浮游植物提供8%～10%和21.6%的N和P,释放溶解有机碳速率为1.0 μmol C·g^-1·d^-1.水母腐烂时总氮和总磷的释放速率可达4000 μmol N·kg^-1·d^-1和120 μmol P·kg^-1·d^-1,溶解有机碳的释放速率为30 μmol C·g^-1·d^-1;水母腐烂可影响水体的酸碱度与溶解氧含量,导致水体严重酸化与缺氧/无氧,pH降幅为1.3,平均耗氧量可达32.8 μmol·kg^-1·h^-1.水母旺发还可引起某些鱼类与浮游动物生物量的减少与重新分布,浮游微生物增加,间接导致浮游植物增加,引起海洋初级生产的异常.
     

Early Life History of the ‘Irukandji’ Jellyfish Carukia barnesi

Adult medusae of Carukia barnesi were collected near Double Island, North Queensland Australia. From 73 specimens, 8 males and 15 females spawned under laboratory conditions. These gametes were artificially mixed which resulted in fertilized eggs. Post fertilization, most eggs developed to an encapsulated planula stage and then paused for between six days and six months prior to hatching as ciliated planulae. The paused stage planulae were negatively buoyant and adhered to substrate. The first planula was produced six days post fertilization, lacked larval ocelli, remained stationary, or moved very slowly for two days prior to metamorphosis into primary polyps. Mature polyps reproduced through asexual reproduction via lateral budding producing ciliated swimming polyps, which in turn settled and developed into secondary polyps. Medusae production for this species was in the form of monodisc strobilation, which left behind polyps able to continue asexual reproduction.     

The potential importance of podocysts to the formation of scyphozoan blooms: a review

Podocysts are cysts with stored reserves of organic compounds produced beneath the pedal discs of polyps of scyphozoans in the orders Rhizostomae (suborder Dactyliophorae) and Semaeostomae. They excyst small polyps that develop into fully active polyps (scyphistomae) capable of further podocyst production and of medusa production by strobilation. They contribute to increasing the number of polyps and also to survival through seasonal periods of reduced food availability or predation. These attributes may help support scyphozoan blooms, but as yet there are few quantitative data. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

Environmental control of phase transition and polyp survival of a massive-outbreaker jellyfish

A number of causes have been proposed to account for the occurrence of gelatinous zooplankton (both jellyfish and ctenophore) blooms. Jellyfish species have a complex life history involving a benthic asexual phase (polyp) and a pelagic sexual phase (medusa). Strong environmental control of jellyfish life cycles is suspected, but not fully understood. This study presents a comprehensive analysis on the physicochemical conditions that control the survival and phase transition of Cotylorhiza tuberculata; a scyphozoan that generates large outbreaks in the Mediterranean Sea. Laboratory experiments indicated that the influence of temperature on strobilation and polyp survival was the critical factor controlling the capacity of this species to proliferate. Early life stages were less sensitive to other factors such as salinity variations or the competitive advantage provided by zooxanthellae in a context of coastal eutrophication. Coherently with laboratory results, the presence/absence of outbreaks of this jellyfish in a particular year seems to be driven by temperature. This is the first time the environmental forcing of the mechanism driving the life cycle of a jellyfish has been disentangled via laboratory experimentation. Projecting this understanding to a field population under climatological variability results in a pattern coherent with in situ records.     

Environmental factors inducing the transformation of polyp into medusae in <Emphasis Type="Italic">Aurelia aurita</Emphasis> (Scyphozoa)

The transformation of polyp into medusa is one of the most interesting processes in the life cycle of cnidarians. In the polyps of the class Scyphozoa this transformation occurs in the form of strobilation, which is the transverse fission of polyps with the formation of discoidal ephyrae. At present, the endogenous regulation of strobilation in one of scyphozoans, Aurelia aurita, is being investigated by the methods of molecular biology (Fuchs et al., 2014). However, it is still unclear which key environmental factors induce this process. The main purposes of this review are to summarize the literature data on the conditions in which strobilation in A. aurita occurs in nature and in the laboratory and to try to identify the environmental factors that are most likely to play a signaling role in strobilation.     

Evolution and development of scyphozoan jellyfish

Scyphozoan jellyfish, or scyphomedusae, are conspicuous members of many ocean ecosystems, and have large impacts on human health and industry. Most scyphomedusae are the final stage in a complex life cycle that also includes two intermediate stages: the larval planula and benthic polyp. In species with all three life‐cycle stages, the metamorphosis of a polyp into a juvenile scyphomedusa (ephyra) is termed strobilation, and polyps can produce one ephyra (termed monodisc strobilation) or many ephyrae (termed polydisc strobilation). In contrast to species with planula, polyp and medusa stages, a handful of scyphozoan species possess modified life cycles with reduced or absent stages. The evolutionary patterns associated with strobilation and life‐cycle type have not been thoroughly investigated, and many studies of ephyra development and strobilation induction are not yet synthesized. Herein, I place the development of scyphomedusae in an evolutionary context. I first review the current evolutionary hypotheses for Scyphozoa. Next, I review what is known about scyphomedusa development across a broad diversity of species, including the first signs of strobilation, the formation of strobila segments, and the morphogenesis of ephyrae. I then review cases where the canonical scyphozoan life cycle has been modified, and take advantage of phylogenetic hypotheses to place these observations in an evolutionary context. I show that the evolution of monodisc strobilation occurred at least twice, and that the loss of intermediate life‐cycle stages occurred several times independently; by contrast, the reduction of the medusa stage appears to have occurred within a single clade. I then briefly review the major natural cues of strobilation induction. Finally, I summarize what is currently known about the molecular mechanisms of strobilation induction and ephyra development. I conclude with suggestions for future directions in the field.     

Irukandji jellyfish polyps exhibit tolerance to interacting climate change stressors

Increasing ocean temperatures and strengthening boundary currents have caused the poleward migration of many marine species. Cubozoan jellyfish known to cause Irukandji syndrome have historically been confined to tropical waters but may be expanding into subtropical regions. Here, we examine the interactive effects of warming and acidification on the population dynamics of polyps of an Irukandji jellyfish, Alatina nr mordens, and the formation of statoliths in newly metamorphosed medusae, to determine if this jellyfish could tolerate future conditions predicted for southeast Queensland (SEQ), Australia. Two experiments, examining the orthogonal factors of temperature and pH, were undertaken. Experiment 1 mimicked the current, ca. 2050 and ca. 2100 summer temperature and pH conditions predicted for SEQ using A1F1 scenarios (temperature: 25, 27, 29 °C; pH: 7.9, 7.8, 7.6) and Experiment 2 mimicked current and future winter conditions (18 and 22 °C, pH 7.9, 7.8, 7.6). All polyps in Experiment 1 survived and budded. Fewer polyps budded in the lower pH treatments; however, patterns varied slightly among temperature treatments. Statoliths at pH 7.6 were 24% narrower than those at pH 7.8 and 7.9. Most polyps survived the winter conditions mimicked by Experiment 2 but only polyps in the 22 °C, pH 7.9 treatment increased significantly. The current absence of A. nr mordens medusae in SEQ, despite the polyps' ability to tolerate the current temperature and pH conditions, suggests that ecological, rather than abiotic factors currently limit their distribution. Observations that budding was lower under low pH treatments suggest that rates of asexual reproduction will likely be much slower in the future. We consider that A. nr mordens polyps are likely to tolerate future conditions but are unlikely to thrive in the long term. However, if polyps can overcome potential ecological boundaries and acidification proceeds slowly A. nr mordens could expand polewards in the short term.     

Single and combined effects of two trace elements (Cd and Cu) on the asexual reproduction of Aurelia sp. polyps

Aquatic Ecology - Jellyfish blooms are an increasingly common event in our seas. Occurring via polyps’ asexual reproduction induced by human stresses, they represent a hazard for ecosystems...     

Pre-exposure to simultaneous,but not individual,climate change stressors limits acclimation capacity of Irukandji jellyfish polyps to predicted climate scenarios

Researchers have investigated the immediate effects of end-of-century climate change scenarios on many marine species, yet it remains unclear whether we can reliably predict how marine species may respond to future conditions because biota may become either more or less resistant over time. Here, we examined the role of pre-exposure to elevated temperature and reduced pH in mitigating the potential negative effects of future ocean conditions on polyps of a dangerous Irukandji jellyfish Alatina alata. We pre-exposed polyps to elevated temperature (28 °C) and reduced pH (7.6), in a full factorial experiment that ran for 14 d. We secondarily exposed original polyps and their daughter polyps to either current (pH 8.0, 25 °C) or future conditions (pH 7.6, 28 °C) for a further 34 d to assess potential phenotypic plastic responses and whether asexual offspring could benefit from parental pre-exposure. Polyp fitness was characterised as asexual reproduction, respiration, feeding, and protein concentrations. Pre-exposure to elevated temperature alone partially mitigated the negative effects of future conditions on polyp fitness, while pre-exposure to reduced pH in isolation completely mitigated the negative effects of future conditions on polyp fitness. Pre-exposure to the dual stressors, however, reduced fitness under future conditions relative to those in the control treatment. Under future conditions, polyps had higher respiration rates regardless of the conditions they were pre-exposed to, suggesting that metabolic rates will be higher under future conditions. Parent and daughter polyps responded similarly to the various treatments tested, demonstrating that parental pre-exposure did not confer any benefit to asexual offspring under future conditions. Importantly, we demonstrate that while pre-exposure to the stressors individually may allow Irukandji polyps to acclimate over short timescales, the stressors are unlikely to occur in isolation in the long term, and thus, warming and acidification in parallel may prevent polyp populations from acclimating to future ocean conditions.

     

Light intensity influences the production and translocation of fatty acids by zooxanthellae in the jellyfish Cassiopea sp.

The influence of light intensity on the fatty acid profiles of the scyphozoan jellyfish Cassiopea sp. and its endosymbiotic zooxanthellae was investigated using a manipulative experiment. The aims of the study were to: 1) identify changes related to light intensity in the fatty acid profiles of the host jellyfish and zooxanthellae; 2) determine if jellyfish exposed to low light intensities compensated for reduced rates of photosynthesis by increasing heterotrophic feeding; and 3) determine if concentrations of zooxanthellae and chlorophyll a (chl a) increased in jellyfish exposed to reduced light intensity. Jellyfish were collected from an artificial urban tidal lake in southeast Queensland, Australia. Two were frozen for immediate analysis and 15 were randomly allocated to each of nine mesocosms. Three replicate mesocosms were then randomly allocated to each of three light treatments: 100%, 25%, and 10% PAR. The mesocosms were supplied with unfiltered, continuous flowing seawater and jellyfish fed on natural zooplankton, supplemented with frozen Mysis shrimp. Three jellyfish were sampled, with replacement, from each mesocosm 3, 15, 22, 39 and 69 days after the experiment commenced. Fatty acids as methyl esters in the host tissue (mesoglea) and zooxanthellae were determined separately using gas chromatography and verified by mass spectrometry. The fatty acid profiles of the host jellyfish and zooxanthellae remained unchanged in the 100% PAR treatment throughout the experiment but varied in the lower light treatments. A decrease in light intensity caused a reduction in the concentrations of some polyunsaturated fatty acids such as 18:1ω9 and 18:4ω3 in the zooxanthellae, the latter being abundant in dinoflagellates. Concomitantly, the concentrations of these fatty acids increased in the host tissues, suggesting a possible transfer of zooxanthellate fatty acids to the jellyfish. Jellyfish in the 10% PAR treatment shrank during the experiment and their fatty acid profiles did not reflect any shift towards increased heterotrophy. On days 22 and 69 concentrations of chl a, zooxanthellae and [chl a] zooxanthella^− 1 were determined. [chl a] and [chl a] zooxanthella^− 1, initially increased in the lower light treatments but decreased by the end of the experiment indicating that jellyfish may adapt to reduced light intensity in the short-term but that long-term exposure to reduced light results in compromised performance.     

Identification key for young ephyrae: a first step for early detection of jellyfish blooms

Although jellyfish blooms are a focus of recent research, the roles that the developmental stages of species play are underestimated. Planulae, polyps and ephyrae are inconspicuous and often overlooked. The importance of production of ephyrae from the sessile polyps has become more apparent. Our objective was to establish an identification system for early ephyrae of scyphozoan species in plankton samples. We studied ephyrae of 18 species. Standard measurements were introduced and the variability of marginal lappets analysed. Characters differentiating the 18 species are described. Photographs and drawings of each species are presented as a catalogue of ephyrae of these species. We developed a key for identification of the 18 species.     

Substrate preferences of scyphozoan <Emphasis Type="Italic">Aurelia labiata</Emphasis> polyps among common dock-building materials

New habitat on proliferating marine construction may increase jellyfish polyp populations, and thereby increase jellyfish populations worldwide. In this investigation, we examined planula settlement and polyp immigration rates of the scyphozoan Aurelia labiata Chamisso & Eysenhardt, 1821 on six common dock-building materials. The planulae and polyps preferred plastics (expanded polystyrenes, low and high density polyethylene) to rubber and treated wood when choosing habitat on man-made surfaces. Substrate surface texture and the presence/absence of anti-fouling chemicals are discussed as possible causes for these substrate preferences. This study illustrates the potential effects of different man-made structures on jellyfish populations, and provides useful information to coastal managers and port authorities for reduction of biofouling and jellyfish bloom effects. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

Indomethacin induction of metamorphosis from the asexual stage to sexual stage in the moon jellyfish, Aurelia aurita

We found while screening a chemical library that indomethacin, an inhibitor of prostaglandin biosynthesis, induced strobilation (metamorphosis from the asexual to sexual stage) in the moon jellyfish, Aurelia aurita. Indomethacin initiated strobilation in a dose-dependent manner, but was not involved in the progression of strobilation. Pharmacological experiments suggested that indomethacin could induce strobilation independently of prostaglandin biosynthesis.     

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.