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1. Benthic jellyfish dominate water mixing in mangrove ecosystems

   https://doi.org/10.1073/pnas.2025715118  

   Durieux, David M. ; Du Clos, Kevin T. ; Lewis, David B. ; Gemmell, Brad J. ( July 2021 , Proceedings of the National Academy of Sciences)

   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 jellyfishCassiopeasp. plays a significant role with respect to biogenic contributions to water column mixing within its shallow natural habitat ($<2$m deep). The mixing contribution was determined by high-resolution flow velocimetry methods in both the laboratory and the natural environment. We demonstrate thatCassiopeasp. 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^-1for 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 foundCassiopeasp. are capable of releasing porewater into the water column at an average rate of 2.64 mL⋅h⁻¹per individual. The release of nutrient-rich benthic porewater combined with strong contributions to water column mixing suggests a role forCassiopeasp. as an ecosystem engineer in mangrove habitats.

    

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2. Benthic jellyfish act as suction pumps to facilitate release of interstitial porewater

   https://doi.org/10.1038/s41598-023-30101-4  

   Durieux, David M. ; Scrogham, Gabrielle D. ; Fender, Christian ; Lewis, David B. ; Deban, Stephen M. ; Gemmell, Brad J. ( March 2023 , Scientific Reports)

   Upside-down jellyfish, genusCassiopea(Péron and Lesueur, 1809), are found in shallow coastal habitats in tropical and subtropical regions circumglobally. These animals have previously been demonstrated to produce flow both in the water column as a feeding current, and in the interstitial porewater, where they liberate porewater at rates averaging 2.46 mL h⁻¹. Since porewater inCassiopeahabitat can be nutrient-rich, this is a potential source of nutrient enrichment in these ecosystems. This study experimentally determines that porewater release byCassiopeasp. jellyfish is due to suction pumping, and not the Bernoulli effect. This suggests porewater release is directly coupled to bell pulsation rate, and unlike vertical jet flux, should be unaffected by population density. In addition, we show that bell pulsation rate is positively correlated with temperature, and negatively correlated with animal size. As such, we would predict an increase in the release of nutrient-rich porewater during the warm summer months. Furthermore, we show that, at our field site in Lido Key, Florida, at the northernmost limit ofCassiopearange, population densities decline during the winter, increasing seasonal differences in porewater release.

    

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

   https://doi.org/10.1038/s42003-020-0777-8  

   Ames, Cheryl L. ; Klompen, Anna M. L. ; Badhiwala, Krishna ; Muffett, Kade ; Reft, Abigail J. ; Kumar, Mehr ; Janssen, Jennie D. ; Schultzhaus, Janna N. ; Field, Lauren D. ; Muroski, Megan E. ; et al ( February 2020 , Communications Biology)

   Snorkelers in mangrove forest waters inhabited by the upside-down jellyfishCassiopea xamachanareport 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 describeC. xamachanastinging-cell structures that we term cassiosomes. These structures are released withinC. xamachanamucus 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 asC. xamachana(Class Scyphozoa; Order Rhizostomeae), categorized as either motile (ciliated) or nonmotile types. This inaugural study provides a qualitative assessment of the stinging contents ofC. xamachanamucus and implicates mucus containing cassiosomes and free intact nematocytes as the cause of stinging water.

    

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4. Symbiont genotype influences holobiont response to increased temperature

   https://doi.org/10.1038/s41598-022-23244-3  

   Moffat, Jennica J. ; Coffroth, Mary Alice ; Wallingford, Piper D. ; terHorst, Casey P. ( November 2022 , Scientific Reports)

   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 jellyfishCassiopea xamachanato 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.

    

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

   https://doi.org/10.1093/gbe/evac172  

   Steinworth, Bailey M ; Martindale, Mark Q ; Ryan, Joseph F ( January 2023 , Genome Biology and Evolution)

   Valverde, Selene Fernández (Ed.)

   Abstract 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. 

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