Upside-down Jellyfish Cassiopea Research Articles

Asymmetrical bleaching of upside-down jellyfish Cassiopea during high water temperatures in Cuba

Asymmetrical bleaching of upside-down jellyfish Cassiopea during high water temperatures in Cuba

Host starvation and in hospite degradation of algal symbionts shape the heat stress response of the Cassiopea-Symbiodiniaceae symbiosis

BackgroundGlobal warming is causing large-scale disruption of cnidarian-Symbiodiniaceae symbioses fundamental to major marine ecosystems, such as coral reefs. However, the mechanisms by which heat stress perturbs these symbiotic partnerships remain poorly understood. In this context, the upside-down jellyfish Cassiopea has emerged as a powerful experimental model system.ResultsWe combined a controlled heat stress experiment with isotope labeling and correlative SEM-NanoSIMS imaging to show that host starvation is a central component in the chain of events that ultimately leads to the collapse of the Cassiopea holobiont. Heat stress caused an increase in catabolic activity and a depletion of carbon reserves in the unfed host, concurrent with a reduction in the supply of photosynthates from its algal symbionts. This state of host starvation was accompanied by pronounced in hospite degradation of algal symbionts, which may be a distinct feature of the heat stress response of Cassiopea. Interestingly, this loss of symbionts by degradation was concealed by body shrinkage of the starving animals, resulting in what could be referred to as “invisible” bleaching.ConclusionsOverall, our study highlights the importance of the nutritional status in the heat stress response of the Cassiopea holobiont. Compared with other symbiotic cnidarians, the large mesoglea of Cassiopea, with its structural sugar and protein content, may constitute an energy reservoir capable of delaying starvation. It seems plausible that this anatomical feature at least partly contributes to the relatively high stress tolerance of these animals in rapidly warming oceans.7jQYTVpxtJyVhU5epTFb61Video

Non-invasive investigation of the morphology and optical properties of the upside-down jellyfish Cassiopea with optical coherence tomography.

The jellyfish Cassiopea largely cover their carbon demand via photosynthates produced by microalgal endosymbionts, but how holobiont morphology and tissue optical properties affect the light microclimate and symbiont photosynthesis in Cassiopea remain unexplored. Here, we use optical coherence tomography (OCT) to study the morphology of Cassiopea medusae at high spatial resolution. We include detailed 3D reconstructions of external micromorphology, and show the spatial distribution of endosymbionts and white granules in the bell tissue. Furthermore, we use OCT data to extract inherent optical properties from light-scattering white granules in Cassiopea, and show that granules enhance local light-availability for symbionts in close proximity. Individual granules had a scattering coefficient of µs = 200-300 cm-1, and scattering anisotropy factor of g = 0.7, while large tissue-regions filled with white granules had a lower µs = 40-100 cm-1, and g = 0.8-0.9. We combined OCT information with isotopic labelling experiments to investigate the effect of enhanced light-availability in whitish tissue regions. Endosymbionts located in whitish tissue exhibited significantly higher carbon fixation compared to symbionts in anastomosing tissue (i.e. tissue without light-scattering white granules). Our findings support previous suggestions that white granules in Cassiopea play an important role in the host modulation of the light-microenvironment.

Comparative Genomic Insights into Bacterial Induction of Larval Settlement and Metamorphosis in the Upside-Down Jellyfish Cassiopea.

Bacteria are important mediators of the larval transition from pelagic to benthic environments for marine organisms. Bacteria can therefore dictate species distribution and success of an individual. Despite the importance of marine bacteria to animal ecology, the identity of inductive microbes for many invertebrates are unknown. Here, we report the first successful isolation of bacteria from natural substrates capable of inducing settlement and metamorphosis of the planula larvae stage of a true jellyfish, the upside-down jellyfish Cassiopea xamachana. Inductive bacteria belonged to multiple phyla, with various capacity to induce settlement and metamorphosis. The most inductive isolates belonged to the genus Pseudoalteromonas, a marine bacterium known to induce the pelago-benthic transition in other marine invertebrates. In sequencing the genome of the isolated Pseudoalteromonas and a semiinductive Vibrio, we found biosynthetic pathways previously implicated in larval settlement were absent in Cassiopea inducing taxa. We instead identified other candidate biosynthetic gene clusters involved in larval metamorphosis. These findings could provide hints to the ecological success of C. xamachana compared to sympatric congeneric species within mangrove environments and provide avenues to investigate the evolution of animal-microbe interactions. IMPORTANCE The pelagic to benthic transition for the larvae of many marine invertebrate species are thought to be triggered by microbial cues. The microbial species and exact cue that initiates this transition remains unknown for many animals. Here, we identify two bacterial species, a Pseudoalteromonas and a Vibrio, isolated from natural substrate that induce settlement and metamorphosis of the upside-down jellyfish Cassiopea xamachana. Genomic sequencing revealed both isolates lacked genes known to induce the life history transition in other marine invertebrates. Instead, we identified other gene clusters that may be important for jellyfish settlement and metamorphosis. This study is the first step to identifying the bacterial cue for C. xamachana, an ecologically important species to coastal ecosystems and an emerging model system. Understanding the bacterial cues provides insight into marine invertebrate ecology and evolution of animal-microbe interactions.

Battle for the mounds: Niche competition between upside-down jellyfish and invasive seagrass.

In tropical ecosystems, autotroph organisms are continuously competing for space, with some plant species benefiting from disturbances such as fire, grazing, or bioturbation that clear habitats (Pulsford et al., 2016). These disturbances can open up layers of vegetation, thereby promoting the colonization of opportunistic species that would have been competitively inferior without disturbance (Castorani et al., 2018). Opportunistic fast-growing species also include often invasive species that are therefore also likely to increase in dominance after disturbance (Altman & Whitlatch, 2007). In seagrass meadows in the southern Caribbean, we observed that the invasive marine plant Halophila stipulacea uses bioturbation mounds created by burrowing infauna such as sea cucumbers and shrimp (see Suchanek, 1983) to colonize new habitats (Figure 1a,b). On Bonaire and Curaçao, in habitats with ~100% native Thalassia testudinum cover, invasive H. stipulacea often at first only occurred on bioturbation mounds that smothered native T. testudinum seagrass, likely to be due to fragmentation and subsequent settlement (Smulders et al., 2017). These observations suggest that bioturbation mounds serve as starting points for further invasion (Figure 1c). These bioturbation mounds add a different kind of disturbance as a mechanism to free up space to settle and expand than previously described for invasive marine plants (e.g., Christianen et al., 2019; Hernández-Delgado et al., 2020). This interaction between invasive marine plants and burrowing organisms could disrupt the natural balance between opportunists and climax species within the ecosystem. Invasive species may compete with native weak competitors in newly created niches after disturbance (Peltzer et al., 2009). This can lead to the co-existence or decline of native species when these are weak competitors and are being pushed out by the invasive species (Altman & Whitlatch, 2007; Hobbs et al., 2009). In this paper, we report evidence of a novel ecological interaction in a tropical seagrass ecosystem between two autotroph species, the invasive seagrass H. stipulacea and the native upside-down jellyfish Cassiopea spp. We discuss the ecological implications and suggest future directions for research. After our first observation, our curiosity increased as we saw that, on Curaçao, the bioturbation mounds often became occupied by a combination of upside-down jellyfish and shoots of H. stipulacea (Figure 1d) that seem to occupy the same niche. Upside-down jellyfish belonging to the genus Cassiopea (hereafter referred to as Cassiopea) have photosynthesizing dinoflagellates as symbionts, and have a benthic lifestyle associated with Caribbean mangrove, seagrass, and coral ecosystems (Niggl & Wild, 2010). To quantify the preference of invasive seagrass and Cassiopea for bioturbation mounds in seagrass meadows and to study potential niche competition, we conducted a pilot experiment on Curaçao. We monitored 10 natural bioturbation mounds, five artificial bioturbation mounds, and five vegetated plots without bioturbation every 3 days for 45 days. All treatments were situated between 1 and 2.3 m in depth and randomized over space with at least 2 m in between plots, which resembled the average natural mound density in the larger area. The artificial bioturbation mounds were made of sediment collected nearby the study site and mimicked the average dimensions of the natural bioturbation mounds (diameter 40 cm; maximum height 20 cm). For each treatment, plots of 0.5 × 0.5 m were marked with PVC poles. Within each plot, a circle (40 cm diameter) was marked with six bamboo skewers, and all seagrass shoots (T. testudinum and H. stipulacea) and Cassiopea individuals within this circle were counted at each sampling moment. The plots were all situated in a mixed seagrass meadow dominated by T. testudinum with a sparse H. stipulacea understory. The results from our pilot experiment suggest that H. stipulacea and Cassiopea both prefer niches where most bare sediment is available. H. stipulacea shoot development was 1.9 ± 0.3 shoots day−1 on artificial mounds compared with 1.6 ± 0.5 shoots day−1 on natural bioturbation mounds and 1.0 ± 0.4 shoots day−1 on vegetated plots (one-way ANOVA, F(2,17) = 0.624, p = 0.55). For Cassiopea, we found an average occurrence of 9.5 ± 5.0 individuals on natural bioturbation mounds, followed by 5.6 ± 1.6 individuals on artificial mounds and 1.4 ± 3.3 individuals in vegetated plots (Kruskal-Wallis, H(2) = 4.118, p = 0.13). Additionally, we observed that Cassiopea individuals spent less time in vegetated seagrass habitat (~1 day) and stayed longer on bare (artificial) bioturbation mounds (>10 days), suggesting that the individuals are mostly passing through habitats with high seagrass cover selecting open spaces to settle (corresponding to findings of Niggl & Wild, 2010). Average (±SE) Thalassia testudinum shoot growth was low in each treatment (0.04 ± 0.02 shoots day−1). Therefore, the data from this pilot experiment confirmed our observations that both Cassiopea and H. stipulacea prefer open habitats created by bioturbation activity and are in niche competition. Both the photosynthetic invertebrate and invasive seagrass are likely to be competing because of their similar requirements for light and space. Our next question was which species will win this competition, or is co-existence possible? To explore the relationship between the presence of Cassiopea and H. stipulacea and their potential competitive exclusion or co-existence, we pooled the artificial and natural bioturbation plots and visualized the average number of H. stipulacea and Cassiopea individuals over time (Figure 2a). Densities of H. stipulacea steadily increased over time, while Cassiopea showed a peak halfway and decreasing densities toward the end of the experiment. To further visualize the differences in dynamics between plots, we compared the species composition at the end of the experiment (based on the ratio of H. stipulacea shoots:Cassiopea individuals) (Figure 2b). After 45 days, H. stipulacea was dominant in 80% (=12 out of 15) of the plots. In the remaining 20% of the plots, no shoots of H. stipulacea were observed during the whole experimental period and only Cassiopea was present at the end of the experiment. Therefore, in all plots where at least one H. stipulacea shoot started growing, the invasive seagrass became dominant relative to Cassiopea within 1.5 months. This is a different outcome for the seagrass–Cassiopea interaction suggested by Stoner et al. (2014), who discussed that high densities of Cassiopea may negatively impact seagrass cover through shading or other processes. Additionally, 27% of the plots were exclusively covered with H. stipulacea at the end of the experiment, while all plots had Cassiopea individuals present at some point during the experiment. This corresponded with our observations in the field: when the bioturbation mounds gradually became invaded by invasive seagrass, the Cassiopea individuals were seen leaving the plots, with the last remaining individuals positioning themselves vertically between the leaves (Figure 2c). We report a novel interaction between an invertebrate with photosynthetic symbionts and an invasive plant after natural disturbance through bioturbation activity. We hypothesize that the arrival of the invasive H. stipulacea is likely to shift patch dynamics in the seagrass ecosystem and, thereby, niche competition between seagrasses and Cassiopea. Within the native seagrass community dominated by T. testudinum, bioturbators are limited by strong root-rhizome networks (Bernard et al., 2019). These open habitats are thus created at a low frequency, but remain stable for a considerable time because T. testudinum does not quickly recover after disturbance (O'Brien et al., 2018). Native Cassiopea can therefore stay for a long period of time in the open habitat created by bioturbators. After the introduction of the invasive seagrass, bioturbation mounds are quickly covered by invasive shoots. In time, as the cover of invasive seagrass increases, we predict that the bioturbation frequency will increase (Figure 1c). Biannual seagrass monitoring in Lac Bay, Bonaire since the seagrass invasion started (2011) provides the opportunity to explore this relationship. Previously we have shown that cross-sections of this bay reflect a gradient of invasion history through time (Christianen et al., 2019; Smulders et al., 2017). Based on this monitoring data, we compared the number of invasive H. stipulacea shoots and bioturbation mounds in habitats that have been recently invaded to habitats that have been invaded for a longer time within 12 transects along the invasion gradient on Bonaire. Each transect consisted of four to six monitoring points (1 m2), which were at least 20 m apart, and each point along the transect was situated either in a long-term or recently invaded habitat. Seagrass and bioturbation data were collected in February and March 2022, first averaged per habitat per transect and then compared between habitats (N = 12). We found that there was a significantly higher number of bioturbation mounds (paired t-test, t(11) = 2.983, p = 0.012) as well as H. stipulacea shoots (paired Wilcoxon rank-sum test, V = 64, p = 0.007) in areas that had been invaded for a longer time (2.8 ± 0.2 mounds m−2, 767.0 ± 245.6 shoots m−2) compared to recently invaded areas (1.6 ± 0.2 mounds m−2, 140.6 ± 55.1 shoots m−2). We hypothesize that this trend can be explained by the fact that plant species with colonizing traits such as H. stipulacea have a shallow and low biomass root system. This provides a more favorable habitat for burrowing animals, as found for squirrel mounds that show a higher density in areas with more invasive cheatgrass, which is structurally less complex (Blank et al., 2013). Therefore, there is likely to be a more frequent creation of bare habitats, but these habitats do not persist as the invasive seagrass H. stipulacea can quickly cover the bioturbation mounds. Cassiopea will thus have to increase its moving frequency between these mounds, which alters its metabolic costs and may potentially impact its survival. Our preliminary data suggest that there is competition between the native opportunist species, the photosynthesizing Cassiopea spp., and the fast-growing invasive seagrass H. stipulacea within niches created by bioturbation activity. A suggestion for future work would be to monitor the bioturbation frequency and reproductive success of Cassiopea over time in invaded ecosystems. Tests to determine if invasive seagrass generally wins this competition, as our preliminary data suggest, or under which conditions co-existence may be possible, are recommended (cf. Valladares et al., 2015). Overall, the detected pattern involving invasive seagrass, native jellyfish, and bioturbating ecosystem engineers has the potential to drive patch dynamics within these vegetated marine ecosystems. This project was carried out as part of the project “Global defaunation and plant invasion: cascading effects on seagrass ecosystem services” appointed to Marjolijn J. A. Christianen (NWO 016.Veni.181.002) as well as under the program of the Netherlands Earth System Science Centre (NESSC). Naomi Slikboer was supported by Stichting Jo Kolk Studiefonds and Stichting Alberta Mennega. We thank Laura Oosting for data collection of the transects on Bonaire, Mark J. A. Vermeij and others at Carmabi, Curaçao for providing field and laboratory support, and Javier A. V. Diaz for help during site selection on Curaçao. Last, we thank Laura L. Govers who contributed to the first observations that led to this work. All authors affirm that they have no conflicts of interest to declare. Data (Smulders et al., 2023) are available in 4TU.Researchdata at https://doi.org/10.4121/21803667.

Reproductive cycle and gonadal output of the Lessepsian jellyfish Cassiopea andromeda in NW Sicily (Central Mediterranean Sea).

Knowledge of the reproductive strategy is a key prerequisite to predict population dynamics and potential invasiveness of both native and non-indigenous outbreak-forming species. In 2014 the Lessepsian upside-down jellyfish Cassiopea andromeda reached the harbor of Palermo (NW Sicily, Thyrrenian Sea), to date its established westernmost outpost in the Mediterranean Sea. To predict C. andromeda reproductive success in its novel habitat, gonad histology was carried out to record the number and size of mature and immature oocytes. Both male and female simultaneously presented gametes at all stages of development suggesting an asynchronous, yet apparently continuous, reproduction strategy. Indeed, oogenesis was observed throughout the year from pre-vitellogenic, vitellogenetic, and late-vitellogenetic to mature oocytes suggesting multiple reproductive events, as known in other Mediterranean Rhizostomeae. Oocytes were found from May to December, with two seasonal peaks of abundance (late spring = 392 and autumn = 272), suggesting imminent spawning events. Further, jellyfish size varied significantly throughout the year, with maximum diameter (up to 24 cm) in summer, and minimum diameter (6 cm) in winter. Small-sized jellyfish in winter belong to the new cohort, most probably arising from intense summer strobilation of polyps. Late spring fertilization, planula development, and metamorphosis, followed by polyp strobilation in the summer months, may explain the late appearance of a new jellyfish cohort, likely coincident with that recorded throughout winter.

Gene Loss may have Shaped the Cnidarian and Bilaterian Hox and ParaHox Complement.

Hox and ParaHox transcription factors are important for specifying cell fates along the primary body axes during the development of most animals. Within Cnidaria, much of the research on Hox/ParaHox genes has focused on Anthozoa (anemones and corals) and Hydrozoa (hydroids) and has concentrated on the evolution and function of cnidarian Hox genes in relation to their bilaterian counterparts. Here we analyze together the full complement of Hox and ParaHox genes from species representing all four medusozoan classes (Staurozoa, Cubozoa, Hydrozoa, and Scyphozoa) and both anthozoan classes (Octocorallia and Hexacorallia). Our results show that Hox genes involved in patterning the directive axes of anthozoan polyps are absent in the stem leading to Medusozoa. For the first time, we show spatial and temporal expression patterns of Hox and ParaHox genes in the upside-down jellyfish Cassiopea xamachana (Scyphozoa), which are consistent with diversification of medusozoan Hox genes both from anthozoans and within medusozoa. Despite unprecedented taxon sampling, our phylogenetic analyses, like previous studies, are characterized by a lack of clear homology between most cnidarian and bilaterian Hox and Hox-related genes. Unlike previous studies, we propose the hypothesis that the cnidarian-bilaterian ancestor possessed a remarkably large Hox complement and that extensive loss of Hox genes was experienced by both cnidarian and bilaterian lineages.

Symbiont genotype influences holobiont response to increased temperature

As coral reefs face warming oceans and increased coral bleaching, a whitening of the coral due to loss of microalgal endosymbionts, the possibility of evolutionary rescue offers some hope for reef persistence. In tightly linked mutualisms, evolutionary rescue may occur through evolution of the host and/or endosymbionts. Many obligate mutualisms are composed of relatively small, fast-growing symbionts with greater potential to evolve on ecologically relevant time scales than their relatively large, slower growing hosts. Numerous jellyfish species harbor closely related endosymbiont taxa to other cnidarian species such as coral, and are commonly used as a model system for investigating cnidarian mutualisms. We examined the potential for adaptation of the upside-down jellyfish Cassiopea xamachana to increased temperature via evolution of its microalgal endosymbiont, Symbiodinium microadriaticum. We quantified trait variation among five algal genotypes in response to three temperatures (26 °C, 30 °C, and 32 °C) and fitness of hosts infected with each genotype. All genotypes showed positive growth rates at each temperature, but rates of respiration and photosynthesis decreased with increased temperature. Responses varied among genotypes but were unrelated to genetic similarity. The effect of temperature on asexual reproduction and the timing of development in the host also depended on the genotype of the symbiont. Natural selection could favor different algal genotypes at different temperatures, affecting host fitness. This eco-evolutionary interaction may be a critical component of understanding species resilience in increasingly stressful environments.

Complete and rapid regeneration of fragments from the upside-down jellyfish Cassiopea

The upside-down jellyfish Cassiopea increasingly occurs in many (sub-) tropical coastal habitats such as mangrove forests, seagrass meadows, and coral reefs. Its mixotrophic lifestyle and ecophysiological plasticity as well as a high regenerative capacity may be reasons for its success. While the regeneration of umbrella tissue and body structures (i.e. rhopalia and oral arms) was already demonstrated, it remains unclear whether a fully functioning medusa can regenerate from only umbrella tissue. In this study, we thus investigated the regeneration of umbrella fragments over time. We conducted a laboratory experiment for which we used 18 Cassiopea medusae of three different size classes that were cut into two pieces each, one fragment with oral arms and one without. Over a total observation period of 5 weeks, we regularly monitored survival, pulsation behavior, growth and the regeneration pattern of fragments. Findings revealed that 100% of the fragments with oral arms and 88% of the fragments without oral arms survived. Pulsation behavior occurred in all fragments and lasted until the end of the experiment in 94% of all fragments. The umbrella area of fragments without oral arms showed a significantly higher decrease in the first two weeks compared to fragments with oral arms. A complete regeneration of umbrella tissue was observed in all fragments, with and without oral arms alike, and 50% of all fragments even regenerated rhopalia or oral arms as body structures after 33 days. These results suggest an outstanding regenerative capacity of Cassiopea jellyfish after fragmentation. This may contribute to (i) explain the currently observed success of upside-down jellyfish and (ii) extend our knowledge about its regeneration process, which might even act as an asexual reproduction mode in Cassiopea.

Invasive upside-down jellyfish tolerate organic eutrophication and warming

The upside-down jellyfish Cassiopea is a successful invasive organism due to high tolerance of different environmental conditions. So far, some single local or global factor experiments have been conducted to assess the effect on the ecophysiology of Cassiopea, but information about combined factor effects is scarce. Therefore, we performed a 42-d manipulation experiment exposing Cassiopea sp. to a local (organic eutrophication) and global factor (warming) simultaneously, i.e., four different dissolved organic carbon (DOC) concentrations [3 (Control), 10 (Low), 20 (Medium) and 40 (High) mg L–1], followed by a stepwise water temperature increase from 26 to 32 °C, in which we assessed four ecophysiological parameters: respiration, net photosynthesis, gross photosynthesis, and pumping rate. Our results show a steep increase in respiration and simultaneous decline in gross photosynthesis in response to Medium and High DOC enrichment causing medusae in the respective treatments to become net heterotrophic over time. This was accompanied by increases in pumping rates, likely to optimize gas exchange and potentially increase nutrient availability by advection of nutrients trapped in underlying sediments. No effect of warming was found for any of the assessed parameters. The observed transition from auto- to heterotrophy under high DOC concentrations together with the thermal tolerance of Cassiopea sp. aids to understand the current invasive success of members of the genus Cassiopea as nonnative organisms and may shed light on the future of Cassiopea sp. as potential native invaders.

New host record of microhabitat preferences of the Banggai cardinalfish (Pterapogon kauderni) in the introduced habitat in Luwuk waters, Sulawesi

Banggai cardinalfish Pterapogon kauderni is an endemic apogonid fish from Banggai Islands, Central Sulawesi, which is discovered in strong association with black sea urchin (Diadema spp.). These fish also protected themselves from predators associated with sea anemones, hard coral branching, mushroom coral, soft coral, seagrass, and mangrove roots. The Banggai cardinalfish juveniles generally prefer to associate with sea anemones or mushroom corals as microhabitats. However, they are looking for similar microhabitats if they cannot find sea anemones or mushroom coral Heliofungia actiniformis. Microhabitat observation of Banggai cardinalfish was carried out in Luwuk waters, Banggai Regency. The result showed a new host record for juvenile phases of Banggai cardinalfish associated with upside-down jellyfish Cassiopea andromeda as a microhabitat. Further study is needed to represent areas and seasons to get more evidence between the Banggai cardinalfish and jellyfish association concepts.

Benthic jellyfish dominate water mixing in mangrove ecosystems

Water mixing is a critical mechanism in marine habitats that governs many important processes, including nutrient transport. Physical mechanisms, such as winds or tides, are primarily responsible for mixing effects in shallow coastal systems, but the sheltered habitats adjacent to mangroves experience very low turbulence and vertical mixing. The significance of biogenic mixing in pelagic habitats has been investigated but remains unclear. In this study, we show that the upside-down jellyfish Cassiopea sp. plays a significant role with respect to biogenic contributions to water column mixing within its shallow natural habitat ([Formula: see text] m deep). The mixing contribution was determined by high-resolution flow velocimetry methods in both the laboratory and the natural environment. We demonstrate that Cassiopea sp. continuously pump water from the benthos upward in a vertical jet with flow velocities on the scale of centimeters per second. The volumetric flow rate was calculated to be 212 L⋅h-1 for average-sized animals (8.6 cm bell diameter), which translates to turnover of the entire water column every 15 min for a median population density (29 animals per m2). In addition, we found Cassiopea sp. are capable of releasing porewater into the water column at an average rate of 2.64 mL⋅h-1 per individual. The release of nutrient-rich benthic porewater combined with strong contributions to water column mixing suggests a role for Cassiopea sp. as an ecosystem engineer in mangrove habitats.

023 Sleep in a Brainless Animal - The Relationship Between Centralization and Sleep in the Upside-down Jellyfish

Abstract Introduction Though sleep is pervasive in animals, its fundamental roles, and the processes involved in generating the behavior, remain poorly understood. A key outstanding question in sleep regulation is whether sleep is controlled strictly by a top-down mechanism via activity of specific central nervous system (CNS) neurons or is controlled partially by bottom-up signals from neural and non-neural tissue. Recently, we showed that the upside-down jellyfish Cassiopea sleeps, providing an opportunity to study sleep control, regulation, and function in an animal without a CNS. Methods Cassiopea have a decentralized nervous system (DNS) of radially spaced interconnected ganglia called rhopalia along their bell margin that control muscle contractions. The signal to contract is sent to muscle fibers local to the initiating ganglion, and the contraction propagates outwards as a point source wave. We have developed computer programs to detect the controlling ganglion, which allows us to non-invasively determine ganglia activity, and to understand how a simple network of ganglia controls behavior. We are also using immunofluorescence, in situ hybridization, qPCR, and RNAseq to characterize the effect of sleep deprivation (SD) on the jellyfish nervous system. Results We have discovered a temporally centralized form of behavioral control that changes between day and night, and during SD. A subset of ganglia share behavioral control—while some almost never initiate contractions, others are active both day and night, or are mostly day-active or night-active, and SD drastically changes ganglia usage. Regions that increase activity at night are less active the following day, perhaps evidence of homeostatic regulation. Using RNAseq we found that during SD, one nAChRα subunit increases expression ~3.8-fold and we are studying its role in arousal and sleep. Conclusion We are investigating a different kind of nervous system, one that is morphologically decentralized (a network of discrete ganglia), and yet temporally centralized (a subset of ganglia dominate activity control). Wake, sleep, and SD involve different ganglia activity patterns, different levels of centralization, and different gene expression. Thus, temporal centralization could provide a mechanism to explain how local sleep, via a bottom-up mechanism, can result in organismal sleep behavior. Support (if any) UC Berkeley Miller Postdoctoral Fellowship

The puzzling occurrence of the upside-down jellyfish Cassiopea (Cnidaria: Scyphozoa) along the Brazilian coast: a result of several invasion events?

The massive occurrence of jellyfish in several areas of the world is reported annually, but most of the data come from the northern hemisphere and often refer to a restricted group of species that are not in the genus Cassiopea. This study records a massive, clonal and non-native population of Cassiopea and discusses the possible scenarios that resulted in the invasion of the Brazilian coast by these organisms. The results indicate that this jellyfish might have invaded the Brazilian coast multiple times.

Non-indigenous upside-down jellyfish Cassiopea andromeda in shrimp farms (Brazil)

Invasive species are one of the biggest threats to coastal areas. Jellyfish, when found in aquaculture systems, may cause major economic damage; they are already present in many aquaculture facilities in the Mediterranean, Yellow Sea, and Bohai Sea. Herein, for the first time, we describe the occurrence of the upside-down jellyfish (genus Cassiopea) in shrimp (Litopenaeus vannamei) farms. The observed specimens were collected on the equatorial Southwestern Atlantic coast (Northeast Brazil) for identification by genetic sequence data (COI). The results indicate that the jellyfish in aquaculture systems are similar in terms of morphology and genetics to those found in natural environments in Bermuda, Egypt, Hawaii, Florida, and elsewhere in Brazil (Rio de Janeiro) and are related to specimens originally inhabiting the Red Sea (Cassiopea andromeda). In addition, we report the northward expansion of C. andromeda along the Brazilian equatorial margin. Only female jellyfish were observed, which suggests that the maintenance and spread of the non-indigenous population occur by asexual reproduction. The high abundance and presence of juvenile and adult animals may have major economic impacts on a high-value industry, given the potential of the population to spread to shrimp farms located in tropical mangroves.

First record of upside-down jellyfish <em>Cassiopea andromeda</em> (Forskål, 1775) (Cnidaria: Scyphozoa: Rhizostomeae: Cassiopeidae) from Sri Lanka

The circumtropical upside-down jellyfish Cassiopea andromeda is native to the Indian region, but no scientific documentations are confirming its presence in Sri Lankan waters. Hence in this paper, the occurrence of C. andromeda in Sri Lankan waters is reported for the first time. Species identification was based on several specimens collected from shallow waters of north and east coasts of the country in 2017. The C. andromeda found from Sri Lanka is a mild stinger and so far there are no reports on severe health issues cause to fishers and tourists. Also, this species was identified as a potential ornamental species due to its gorgeous appearance with very high colour variation.

Cassiosomes are stinging-cell structures in the mucus of the upside-down jellyfish Cassiopea xamachana

Snorkelers in mangrove forest waters inhabited by the upside-down jellyfish Cassiopea xamachana report discomfort due to a sensation known as stinging water, the cause of which is unknown. Using a combination of histology, microscopy, microfluidics, videography, molecular biology, and mass spectrometry-based proteomics, we describe C. xamachana stinging-cell structures that we term cassiosomes. These structures are released within C. xamachana mucus and are capable of killing prey. Cassiosomes consist of an outer epithelial layer mainly composed of nematocytes surrounding a core filled by endosymbiotic dinoflagellates hosted within amoebocytes and presumptive mesoglea. Furthermore, we report cassiosome structures in four additional jellyfish species in the same taxonomic group as C. xamachana (Class Scyphozoa; Order Rhizostomeae), categorized as either motile (ciliated) or nonmotile types. This inaugural study provides a qualitative assessment of the stinging contents of C. xamachana mucus and implicates mucus containing cassiosomes and free intact nematocytes as the cause of stinging water.

Regenerative Capacity of the Upside-down Jellyfish Cassiopea xamachana.

This study provides the first observation that umbrellar tissue can lead to the formation of virtually all body structures in jellyfish of the order Rhizostomeae. The regeneration process was observed in two specimens of the upside-down jellyfish Cassiopea xamachana Bigelow, 1892, one housed at the Vienna Zoo, Austria and the other in a laboratory at the University of São Paulo, Brazil. The process was triggered by an injury and ended with the formation of two new sets of body structures. Our observation offers evidence that C. xamachana has a hidden regenerative capacity exceeding that previously recorded.

Risk screening of the potential invasiveness of non-native jellyfishes in the Mediterranean Sea

The aim of the present study was to risk screen 45 jellyfish species (30 hydromedusae, 14 scyphomedusae, one cubomedusa) for their potential invasiveness in the Mediterranean Sea to aid managers in making informed decisions on targeting appropriate species for management. Using the Aquatic Species Invasiveness Screening Kit (AS-ISK), calibrated basic and climate-change threshold assessment scores of 6.5 and 12.5, respectively, were identified for distinguishing reliably between species that pose ‘low-to-medium’ and ‘high’ risk of becoming invasive in the risk assessment area. Using these thresholds, 16 species were classified as high risk, 23 as medium risk and six as low risk under current climate conditions. Whereas, under future climate conditions, 13, 30 and two species, respectively, were classified as high, medium and low risk, respectively. Upside-down jellyfish Cassiopea andromeda, Australian spotted jellyfish Phyllorhiza punctata, sea nettle Chrysaora quinquecirrha and Rhopilema nomadica were the highest-scoring species, with the maximum increase in risk score under predicted climate change conditions being achieved by C. andromeda.

Molecular identity of the non-indigenous Cassiopea sp. from Palermo Harbour (central Mediterranean Sea)

AbstractThe upside-down jellyfish Cassiopea is a benthic scyphozoan, considered a non-indigenous invasive species in the Mediterranean, forming large blooms in eutrophic areas. Taxonomy of the genus Cassiopea is extremely difficult because morphological/meristic characters used are variable within the same species, overlapping among different species, and cryptic species have been identified by molecular markers; nine Cassiopea species are recognized on the basis of molecular study. Mediterranean records of Cassiopea have been ascribed to andromeda species on the basis of a hypothesized invasion pathway from the Suez Canal. In the current study, an analysis of the main morphological characters of the sampled Cassiopea jellyfish from Palermo (Tyrrhenian Sea) was carried out and subsequently, molecular analyses were performed by using COI barcode in order to identify the species. Molecular data were compared with published information in GenBank. Morphological characters were highly variable, but molecular analyses confirmed that Mediterranean Cassiopea specimens belong to andromeda species. Moreover, high values of sequence divergence were found between Mediterranean Cassiopea and the other C. andromeda from the Red Sea, Hawaii and Florida. These results lead to a discussion of possible explanations linked to life history features of the species. Two different explanations are proposed; the first is that Mediterranean C. andromeda, finding a suitable ecological niche good for colonization and proliferation, could have been isolated in Palermo Harbour. The second considers the possibility of multiple introduction events by human transport as demonstrated for other non-indigenous jellyfish; in this case Cassiopea genetic differences increased in the invaded area.