Rhizostoma luteum; a large jellyfish to be rediscovered

Trabajo presentado en el 6th International jellyfish blooms symposium, celebrado en Cape Town del 4 al 6 de noviembre de 2019.Until summer 2012 Rhizostoma luteum was a forgotten species, and even some scientist doubted its occurrence, believing it might be a young Rhizostoma pulmo or a local variation. The first mention of this large Scyphozoa was by Quoy and Gaimard in 1827 from the Strait of Gibraltar (southern Iberian Peninsula). We describe for the first time, the life cycle of this jellyfish and compare it with early life history stages of its sibling species Rhizostoma pulmo and Rhizostoma octopus. We observed only one asexual reproduction mode, which is employed for propagation, consisting of podocyst formation with excystment, subsequent development of scyphistoma, strobilation and liberation of viable ephyra. Furthermore, the development of ephyra to metaephyra was photodocumented, reaching the metaephyra stage in approximately 21-25 days. The life cycle of R. luteum resembles that of its congeners, with the distinction that it has the unique feature of being a brooding species (internal fertilisation with subsequent release of planulae) and under the conditions tested, the predominantly strobilation type observed was monodisc, and not polydisc as with the other two species in the genus Rhizostoma. Thus, to better understand its ecological roles, it is essential to study its life cycle.Peer reviewe

Environmental forcing in early life stages of the scyphozoan jellyfish Rhizostoma luteum

Trabajo presentado en el 6th International jellyfish blooms symposium, celebrado en Cape Town del 4 al 6 de noviembre de 2019.It is important to understand the role of early life stages in the formation of jellyfish outbreaks, whether they are cyclic or in response to climate change, and it has been neglected until recently. The aim of this study was to determine the response to environmental forcing in the early life stages of the scyphozoan jellyfish Rhizostoma luteum. Laboratory experiments were carried out to examine the effects of different temperature and salinity conditions on planula settlement, scyphistoma development, podocyst production, ephyra liberation and development until the metaephyra stage. The results show that the planuae were highly resilient to a wide thermal and salinity window and they settled faster in warmer conditions. However, the scyphistomae showed physiological stress in the warmest (28 °C) and saltiest (38) treatments. Asexual propagation and ephyra growth were greater at mid temperature (23 °C) and in hyposaline (24) conditions. Their ability to grow in hyposaline conditions raises the possibility that some or all reproductive stages may occur in estuaries or other brackish environments. The ongoing ocean warming and the decrease in rainfall are discussed to explore the implications in this jellyfish population dynamics.Peer reviewe

First description of the life cycle of the jellyfish Rhizostoma luteum (Scyphozoa: Rhizostomeae).

Jellyfish blooms are a significant environmental problem that is increasing and may be influenced by anthropocentric practices such as overfishing, pollution, eutrophication, translocation, climate change, and ocean acidification. Many jellyfish have unknown life cycles leading to these blooms. We describe for the first time, the life cycle of scyphozoan jellyfish Rhizostoma luteum from the planula to the young medusa stages, based on laboratory observations. We also provide a preliminary assessment of temperature related to life stages. Comparisons were made with early life history stages of its sibling species Rhizostoma pulmo and Rhizostoma octopus. The life cycle of R. luteum follows the general pattern of metagenesis of scyphozoans. Scyphistoma culture was maintained in filtered seawater at 17-17.5 °C, salinity 37 and light photoperiod (12:12 h light:dark). Scyphistomae were exposed to an experimental temperature descent for two days to test their survival capacity under severe winter conditions. Only one asexual reproduction mode was observed, which is employed for propagation, consisting of podocyst formation with excystment, subsequent development of scyphistoma, strobilation and liberation of viable ephyra. The development of the ephyra to metaephyra was photodocumented, reaching the metaephyra stage in approximately 21-25 days. Young medusae grow rapidly and maturity was reached after a 3-month post-liberation period with a mean bell diameter of 13.27 ± 2.26 cm and wet weight of 181.53 ± 53 g. The life cycle of R. luteum resembles that of its congeners, with the distinction that it has the unique features of being a brooding species (internal fertilisation with subsequent release of planulae) and under the conditions tested, the predominantly strobilation type observed was monodisc, and not polydisc as with the other two species in the genus Rhizostoma. As R. luteum shows sufficient requisite to form blooms if environmental circumstances change, it is important to understand its life cycle