The upside-down jellyfish Cassiopea xamachana (Scyphozoa: Rhizostomeae) has been predominantly studied to understand its interaction with the endosymbiotic dinoflagellate algae Symbiodinium. As an easily culturable and tractable cnidarian model, it is an attractive alternative to stony corals to understanding the mechanisms driving establishment and maintenance of symbiosis. Cassiopea is also unique in requiring the symbiont in order to complete its transition to the adult stage, thereby providing an excellent model to understand symbiosis-driven development and evolution. Recently, the Cassiopea research system has gained interest beyond symbiosis in fields related to embryology, climate ecology, behavior, and more. With these developments, resources Ohdera et al. Cassiopea xamachana System Review including genomes, transcriptomes, and laboratory protocols are steadily increasing. This review provides an overview of the broad range of interdisciplinary research that has utilized the Cassiopea model and highlights the advantages of using the model for future research.

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Bioaccumulation of trace elements in jellyfish has so far received little attention, despite their being prey for many animals from multiple trophic levels and targeted by commercial jellyfish fisheries. Scyphozoan and cubozoan jellyfish were collected over a three year period from across-shelf and along the northern and central Great Barrier Reef, Australia. To test the hypotheses that jellyfishes were able to accumulate elements above ambient background levels, and if there were spatial or temporal variations among species, soft tissue concentrations of 14 trace elements were compared with ambient seawater concentrations. Most elements, including aluminium, arsenic, barium, cadmium, chromium, copper, iron, manganese and zinc were measured at concentrations above ambient seawater levels indicating bioaccumulative capacity. Results showed some regulation of lithium in Cassiopea sp., Cyanea sp. and Mastigias sp., while calcium, magnesium and strontium reflected ambient conditions for all species. Accumulation varied significantly among species and sampling locations. For Mastigias sp. and Netrostoma sp., tissue concentrations of Al, As, Cu, Fe and Zn decreased with distance from the mainland. The hypothesis that jellyfishes are capable of accumulating trace elements was accepted, and their use as biomonitors should be investigated further.

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