Plenary
Cheryl Lewis-Ames – Tohoku University / Smithsonian NMNH
Title: Cassiopea xamachana: The making of a star!
The upside-down jellyfish has soared since its pro-star debut at the 1st International Cassiopea Workshop (ICW) in 2018. Starting with a major review paper, followed by draft genomes and transcriptomes, along with the discovery of sleep, plasticity and fluid dynamics of these spectacular jellyfishes, our knowledge and community base has undergone a stellar explosion. In 1810, when Péron & Lesueur assigned the upside-down jellyfish to the genus Cassiopea after the ancient celebrated constellation “Cassiopeia” it all but guaranteed its future a scientific superstar. I highlight the discovery of cassiosomes and Cassiopea’s role in pioneering the fieldable eDNA sequencing kit (FeDS); findings made possible thanks to the ICW community.
Lior Applebaum – Bar Ilan University
Title: Sleep, DNA damage and repair
Sleep is vital for survival and all animals with a nervous system, ranging from jellyfish, to fish and humans sleep. Although sleep clearly improves brain performance, even invertebrates with simple nerve nets sleep, and the core cellular function of sleep is unclear. We hypothesize that single neurons require sleep. The zebrafish enables the study of the physiology of defined single cells in the context of an intact nervous system in a live animal. We combined imaging of single chromosomes and repair proteins, 3D particle motion analysis, optogenetics stimulation, as well as calcium imaging to study the interaction between sleep, neuronal activity, DNA damage and repair. We found that sleep upregulates nuclear maintenance in neurons.
Brad Gemmell – University of South Florida
Title: Does Cassiopea Act as an Ecosystem Engineer in Mangrove Habitats? Cassiopea spp. are common residents in the shallow, sheltered waters adjacent to stands of red mangrove trees. In these regions, Cassiopea can dominate the benthos with peak densities documented to exceed 100 individuals per square meter (mean 29 ind m-2). Using a variety of techniques from novel in situ particle image velocimetry (PIV) instruments to standard gut content microscopy, our aim was to quantify some of the impacts these animals have within their habitat. We measured the vertical volumetric flow rate to be 212 Lh-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. In addition, we found Cassiopea sp. are capable of releasing porewater into the water column at a rate that can significantly alter nutrients in the water column. We also explored the ability and frequency of these animals to move across the substrate, the impact of temperature and salinity on pulsation rates, as well as quantifying the diet over a 24 hr cycle. We found non-random movement and self-arrangement as well as consumption of large quantities of zooplankton. In this presentation we will discuss and consider these results and more in the context of an ecosystem engineering role for Cassiopea spp.
Presentations
Addie Harrison – University of Arizona
Title: Fluid dynamics of a nematocyst firing and ejection
Nematocysts are stinging organelles found in organisms such as jellyfish, anemones, and hydrozoans. The immersed boundary method is used to couple the elastic equations and the fluid equations to numerically simulate nematocyst firing and ejecting dynamics. Our preliminary results show that the nematocysts ability to accurately hit and puncture a surface it is projected to hit can vary based on the acceleration used to fire as well as the target’s size and makeup.
Marie Strader – Auburn University
Title: Cassiopea as a model to study acclimation and adaptation to global change
Global change is causing shifts in ecosystem dynamics: while some species are suffering from rapid population declines, others possess biological characteristics that promote invasion and proliferation in human-disturbed ecosystems, including Cassiopea. Because Cassiopea can survive in rapidly changing environments, they are an ideal system to investigate mechanisms mediating environment-organism interactions. However, little is known about the natural history of this taxa, species delimitation.
Megan Maloney – Auburn University
Title: Cassiopea sp. exhibit plastic responses to temperature change
In the face of changing climates, some organisms respond by adjusting morphological or physiological characteristics. This plasticity enables some organisms to survive variable environments, whereas others cannot. Cassiopea sp. are highly tolerant to environmental stress which may be due to their ability to regulate bell pulsation. We measured pulsation metrics during a lethal heat stress to address the hypothesis that phenotypic plasticity contributes to their ability to survive.
Louis Schlecker – Smith College
Title: Comparing Heat and Cold Stress in Exaiptasia diaphana
The facultative symbiotic anemone Exaiptasia diaphana is used as a model organism to study symbiotic contributions to host stress resilience. Standard protocols for generating aposymbiotic Exaiptasia include cold shock stress, which is supposedly less stressful than bleaching via heat stress. We subjected Exaiptasia to gradual (1℃/day) and abrupt cold and hot treatments to compare host stress responses.
Caroline Link – New College of Florida
Title: Cassiopea xamachana hosts confer some protective effect to thermosensitive symbionts
We compared the thermotolerance of Symbiodinium (CassEL-1) when in culture versus in hospite within C. xamachana ephyrae. CassEL-1 cultures were thermosensitive, while in hospite communities displayed significantly increased thermotolerance at the onset of treatment but which began to fade after 6 days at 32℃. This suggests that Cassiopea may provide symbionts with some degree of a protective effect during initial stress exposure.
Rachel Wright – Smith College
Title: Symbiotic state modulates interactive stress response in a cnidarian–algal holobiont
Global climate change threatens marine organisms with multiple simultaneous stressors. Here we assess anemone health under four treatments: control, increased light, increased nutrients, increased light+nutrients. We conducted these treatments using five genets of anemones in the symbiotic and aposymbiotic states. Our results demonstrate the importance of assessing the health impacts of combined environmental challenges and highlight how symbiotic state modulates holobiont stress responses.
Madison Emery – Auburn University
Title: Tradeoffs between symbiosis and immunocompetence in Cassiopea sp. polyps following bacterial infection
To investigate the potential tradeoffs between symbiosis and immunity we utilize the facultatively symbiotic Cassiopea polyps to determine the impact of symbiotic state on disease pathology. Symbiotic Cassiopea polyps are more susceptible to both Vibrio coralliilyticus and Serratia marcescens infection relative to their aposymbiotic counterparts. To further investigate this effect we measure polyp physiology.
Christina Hamlet – Bucknell University
Title: Variation in flow through the oral arms of Cassiopea
Cassiopea uses the pulsations of its bell to drive fluid across its oral arms for fluid sampling to feed, remove waste, regulate temperature, among other functions. Fluid flow through the oral arms may be altered depending on the configuration of the structures, allowing the oral arms to act more as solid plates or leaky rakes, depending on the characteristics of the flow and the need of the organisms. I will present work showing how the spacing between structures changes the flow dynamics at the scale of the finest structures of the oral arms (digitata).
Matea Santiago – University of Arizona
Title: Oxygen removal around pulsing soft corals
Soft corals in the family Xenia rhythmically pulse their tentacles to enhance the photosynthesis of their symbionts, similar to the Cassiopea jellyfish. We seek to understand the role of pulsing in oxygen removal near the coral tentacles where the symbiotic algae are located by considering the oxygen to be a passive concentration in the fluid. The length of the resting phase is varied to understand the pulsing motion’s effect on the concentration dynamics. Preliminary results will be presented.
Natalia Lopez-Figueroa – University of South Florida
Title: A Scientometrics Review of the Genus Cassiopea
Members of the Genus Cassiopea have been studied since the 1990s for their semi-sessile benthic behavior and for bearing algal symbionts analogous to their anthozoan counterparts, stony coral, making them excellent laboratory models to study host-symbiont relationships. Historically, research on upside-down jellies has focused on their life history and symbiotic relationships, with most studies carried out in laboratory settings. Much less information is available about their field ecology, though high population densities of upside-down jellies have been linked with human activity in nearshore environments. Recent studies have proposed the use of Cassiopea as bioindicators for detecting nutrient pollution as they appear to thrive on increased nutrient availability. In this review, we assess the published literature of Cassiopea with the goal to identify the major gaps in understanding their field ecology and potential as bioindicators. Using internet-based searches up to October 2021, 102 papers on Cassiopea were located, 77% of the published literature have been lab-based studies, with the remainder being field studies and reviews. Historical papers date back to 1900, with a subsequent exponential increase in numbers of studies, peaking in the 2010–2019 decade. Field studies became more frequent beginning in the early 2000s. This literature review provides a baseline for understanding the existing realm of Cassiopea research and indicates that field-based studies could enhance understanding of their role in anthropogenically-impacted environments.
Shio-Han Hung – King Abdullah University of Science and Technology
Title: Using the Red Sea upside-down jellyfish Cassiopea to study cnidarian-Symbiodiniaceae symbiosis
To understand the molecular mechanisms behind this symbiosis, gene expression profiles between aposymbiotic and symbiotic Cassiopea polyps were compared, revealing genes and pathways putatively involved in symbiosis. We identified 1,227 differentially expressed genes out of 63,340 transcripts, with 560 upregulated and 667 downregulated in symbiotic polyps. GO enrichment analysis indicated that processes linked to lipids, sterols, cholesterol, and membrane transport were upregulated in symbiotic
Justin Darymple – Florida International University
Title: Chemical screening reveals pathways involved in bleaching in cnidarians
Co-investigators: Luciano T. Simonetta, Anthony J. Bellantuono, Matthew DeGennaro
Coral bleaching is the expulsion of intracellular photosymbionts by their coral hosts in response to stress. While bleaching is projected to be a growing problem for the world’s reefs, molecular mechanisms underpinning bleaching remain unclear. We performed a mechanism-agnostic screen to identify underlying candidate pathways in the model symbiotic anthozoan Exaiptasia diaphana. Anemones were exposed to 1,280 human pharmaceuticals for 96 hours before bleaching was assessed by fluorescence. Since pharmaceuticals interact with known targets, this approach represents a novel method for understanding the mechanistic basis of dysbiosis. Preliminary analysis reveals over 70 compounds that cause bleaching in anemones, including medications prescribed for psychiatric disorders, osteoporosis and blood pressure.
Diana Francis – University of California, Berkeley
Title: Homeostasis at the Heart of Sleep in the Jellyfish Cassiopea
We sequenced RNA from baseline and sleep deprived animals and found differential expression (DE) in many sleep-related genes. One nicotinic acetylcholine receptor alpha subunit (nACHRa) is highly DE, and characterization has supported a sleep-related function within the ganglia. Further, we developed RNAi for use in Cassiopea to knockdown target expression and determined that this nACHRa plays a role in regulating sleep homeostasis, as treated animals slept far more in the day (~35%) and less
Michael Abrams – University of California, Berkeley
Title: Homeostasis at the Heart of Sleep in the Jellyfish Cassiopea
By tracking the propensity of ganglia to initiate contractions over days and nights we are able to determine how neural activity changes between sleep and wake in Cassiopea. Long-term ganglia usage hierarchies exist and active ganglia exchange with inactive ganglia over time. Ganglia-network sleep/wake activity patterns can range from being highly specialized to completely unspecialized. Further, ganglia activity in sleep-deprived animals becomes far more sleep/wake specialized.
Amir Harduf – Bar Ilan University
Title: Mechanisms regulating circadian and sleep behavior in the upside-down jellyfish
All animals had to adapt to our planet’s rotation and the day-night cycle, and evolve endogenous pacemakers that drive rhythmic physiology and behavior. The circadian clock is entrained by environmental inputs, such as light and temperature, and regulates rhythmic outputs including the timing of sleep. Sleep is an evolutionarily conserved behavior in all animals, which is regulated by homeostatic and circadian processes. Sleep is crucial to the health of the nervous system and regulates various processes ranging from cellular maintenance to memory and learning. However, why this behavior, which puts the animal under the risk of predation, has evolved, is unclear. Recently, behavioral criteria were used to define the sleep-like state in cnidarians, which are lower basal animals with a simple nerve net. In this study, we utilize the upside-down jellyfish Cassiopea to understand the origin and mechanisms of the circadian clock and the sleep/wake cycle. Cassiopea is a diurnal jellyfish that harbors the photosymbiont Symbiodinium microadraticum (Dinoflagellata; Symbiodiniaceae). We hypothesize that interactions between light, algae photosynthesis, photosymbiosis, ROS, and DNA damage, regulate rhythmic behavior and sleep pressure in Cassiopea. Using custom-made behavioral systems, computational analysis, immunohistochemistry, and molecular analysis, we characterize circadian and sleep mechanisms in both the single neuron and whole organism levels. The results are expected to reveal how sleep has evolved and suggest why it is conserved across phylogeny.
Ranjith Lakshmanan – Indian Council of Agricultural Research – Central Marine Fisheries Research Institute
Title: First-time record of wild ephyrae of Cassiopea spp with complementary notes to the early life-history traits. The present study describes the upside-down jellyfish, Cassiopea ephyrae and young medusa developmental morphology at different time intervals under a controlled rearing system for the first time from Indian waters. The newly released ephyrae of upside-down jellyfish Cassiopea were collected from the primary settlement unit of a slow sand filter facility with the source seawater from the Tuticorin Bay, the Southeast coast of India. The newly liberated ephyrae NLE (1.4-2.5 mm) differs from reported scyphozoan morphogenesis differs in its morphology and development. It has a very long manubrium length (more than half of the central disc diameter), the presence of 16 spatula-shaped velar lappets and 32 outward bent tip rhopalial lappets with zooxanthellae distributed in the mesoglea. The ephyra development starts with the formation of four lips with digitata in the manubrium. As the ephyra grows, the first four gastric filaments develop and form the manubrium, and four oral arms extend to get bifurcated, forming eight early oral arms. This sequence is followed by developing vesicles in the arms and the disc centre in the young medusa. The study revealed that the ephyrae readily accepted live feed in laboratory conditions and recorded substantial growth and morphogenesis to young medusae of Cassiopea spp. In the current present investigation, the development of the ephyrae to young medusa takes 3 to 4 days under controlled laboratory conditions.
Kaden Muffet – Texas A&M – Galveston
Title: Two Cassiopea species coexist in Florida Keys Shallow waters
The extent of Cassiopea diversity within the Florida Keys has long been disputed. Collecting 55 Cassiopea from 8 sites stretching the length of the Keys, we are able to bring more data to bear on this issue. Using COI and 16S, we demonstrate a combination of two species sympatric at multiple sites. The two profiled species, C. xamachana and C. andromeda*, are morphologically cryptic but present in very different proportions (10:1) along the length of the Keys.
Natalia Lopez-Figueroa – University of South Florida
Title: Field experiment on the settlement of the upside-down jellyfish (Genus Cassiopea) in a restored salt pond at Jobos Bay National Estuarine Research Reserve (JBNERR), Puerto Rico
Historically, research on upside-down jellies has focused on their life history and symbiotic relationships, with most studies carried out in laboratory settings. Much less information is available about their field ecology. High population densities of upside-down jellies have been linked with human activity in nearshore environments. For example, Cassiopea blooms have been correlated with human-impact such as dredging in coastal environments. The Jobos Bay Natural Estuarine Research Reserve dredged a salt pond within a salt marsh during habitat restoration of shorebird nesting areas. Shortly after the pond was dredged a Cassiopea outbreak was observed in the pond. We addressed recruitment of this population by testing substrate preference of Cassiopea larvae using settlement-tile experiments. This pilot study was conducted beginning in December 2020. Tiles were deployed in six locations in the salt pond, each set contained five different treatments based on preferred substrates from reports of lab-based experiments. Juvenile Cassiopea were observed on tiles within six weeks of deployment. Environmental data demonstrated a temperature gradient in the salt pond and a wide fluctuation in pH. Nutrient data indicated that sites within the salt pond exhibited nitrate limitation, while water in the channel that enters the lagoon from Jobos Bay showed phosphate limitation. This pilot study provides insight into Cassiopea bloom dynamics in their natural habitat, which opens new horizons for future work with these magnificent organisms.
Raphaël Aguillon – Bar Ilan University
Title: Clock enigma in the sea-anemome Nematostella vectensis
The circadian clock regulates daily oscillations in molecular, physiological, and behavioral processes that anticipate sunrise and sunset in animals ranging from cyanobacteria to cnidarians to humans. The intrinsic clock is driven by environmental cues such as light, food and temperature. Extensive research in invertebrates and vertebrates has characterized the fundamental factors and mechanisms of the molecular clock, which are evolutionarily conserved. It involves multiple negative feedback loops including transcription factors, which oscillate on an approximately 24-hour cycle. One of the key regulators of this mechanism is the conserved transcription factor bHLH CLOCK, which acts in dimers to regulate the expression of clock-controlled genes. The clock gene and its homologues have been identified in all animal clades, including cnidarians, basal metazoans, suggesting that the circadian clock evolved at this stage of animal evolution.
The nocturnal sea anemone Nematostella vectensis has a 24-hour rhythmic behavior in both light and dark and in constant darkness. This free-running behavior in the absence of external signals suggests a functional intrinsic circadian clock. Unconventionally, we found that the orthologous genes of the central clock are rhythmic only in the light/dark cycle. These results call into question the CLOCK protein as a central regulator of the circadian clock in early animal lineages. To test the function of the ancient CLOCK, we generated a CRISPR-mediated clock mutant of N. vectensis. By combining video tracking of behavior, whole transcriptome sequencing, and high-resolution anatomical studies in the clock mutant, we investigate the origin of time in animals.