New description increases number of known species in jellyfish genus from seven to 28

On the basis of genetic analysis of jellyfish specimens held in collections around the world, researchers have reclassified these species in the genus Aurelia, many of which are highly similar. Painstaking descriptions of species are key to conservation strategies.

By André Julião  |  Agência FAPESP – With diameters varying from 10 cm (about the size of a saucer) to 46 cm (as big as a large serving platter), the moon jellyfish Aurelia spp. is almost entirely translucent, with a bluish or pinkish tinge, and is found in coastal environments worldwide. Seven species were recognized until recently, but a study by researchers in Brazil, Argentina and the United States has now raised the number of species in the genus to 28.

The results of the study are reported in the journal PeerJ. The descriptions are essential to new research on Aurelia, one of the most studied jellyfish genera. Delimitation of species also contributes to conservation strategies amid the environmental changes caused by the climate crisis.

“The initial proposal was to try to understand what was happening to these animals along the coast of Brazil, but it expanded when I had a chance to analyze the genus worldwide. It became clear that the matter was more complex, requiring a grasp of the global context before we could establish which species occur in Brazil,” said Jonathan Lawley, first author of the published paper. The study was part of his master’s research at the University of São Paulo’s Institute of Biosciences (IB-USP) in Brazil with a scholarship from FAPESP.

He did some of the research at the Smithsonian Institution’s National Museum of Natural History in the United States, also with FAPESP’s support. He was able to analyze the museum’s large collection in Washington DC, comprising specimens collected from all parts of the planet. While working at the Smithsonian, he also received specimens deposited with other US institutions. Separately, he traveled to Denmark to analyze specimens at the University of Copenhagen’s Museum of Zoology. He realized that differentiation would be impossible on the basis of morphology alone. Although many of the animals displayed no morphological differences at all, genetic analysis showed that they belonged to distinct species.

“Studying jellyfish isn’t easy. The body has only one hard structure and is unlikely to remain intact for a long period so that measurements can be taken. Being gelatinous, they may shrink up to 40% when conserved, as they contain a lot of water. Another important factor is that some species are very similar,” said André Morandini, last author of the published paper. Morandini is a professor at IB-USP and Vice Director of the Center for Marine Biology (CEBIMAR-USP) in São Sebastião, São Paulo state.

The study was part of the FAPESP-funded project “ Recognizing the diversity of jellyfish (Medusozoa, Rhopaliophora)”, with Morandini as principal investigator.

Genetics

The study has contributed to a debate dating back more than 200 years about the number of species in the genus Aurelia. The first species recognized by modern taxonomy was Aurelia aurita, described in 1758 by Linnaeus (Swedish naturalist Carl von Linné, 1707-1778).

Other descriptions were produced, taking the number of proposed species from eight to 13, although some were later invalidated. By the start of this century, three had been accepted as valid besides A. aurita. These were A. labiata, which has a distinct mouth resembling a human lip; A. limbata, found in the Arctic, with a brown bell margin; and A. marginalis, which occurs in the Gulf of Mexico and eastern United States.

Genetic tools were used in 2016 to recognize three more species, A. coerulea, A. relicta and A. solida, all occurring in the Mediterranean. Others were delimited with molecular markers but not formally described because the morphological data available was insufficient for comparison with genetic data.

This latest study combined morphological data with four molecular markers derived from both mitochondrial and nuclear DNA. In some cases, the difference corresponded to only 5% of the genome.

To answer Lawley’s initial question, three species have been identified on the Brazilian coast. They were previously deemed to be just one, A. aurita.

A. insularia is found mainly on islands in the Southeast and South of Brazil, such as Ilha Grande, as well as in the United States (Key Largo, Florida).

A. mianzani is named for Hermes W. Mianzan (1957-2014), an Argentinian researcher who collected some of the specimens that have had their DNA sequenced and contributed significantly to studies of jellyfish in the Southwest Atlantic. The species is found at Praia do Segredo in São Sebastião, and Samborombón Bay in Buenos Aires Province, Argentina.

A. cebimarensi s is named for CEBIMAR-USP, with which the Brazilian researchers involved in the study are affiliated. The specimen that served as a reference for the description was found in São Sebastião at Ponta do Baleeiro, part of a beach called Praia do Cabelo Gordo, where CEBIMAR is located. The species probably inhabits most of the Brazilian coast.

Two other species named for specialists in the field are A. montyi in honor of William “Monty” Graham, Director of the Florida Institute of Oceanography, and A. miyakei, honoring Hiroshi Miyake, a professor at Kitasato University in Japan.

The other newly named species are A. rara, A. ayla, A. smithsoniana, A. columbia and A. malayensis. In addition, four species have been resurrected: A. persea, invalidated after being described in the eighteenth century, and A. clausa, A. dubia and A. hyalina, originally described in the nineteenth century and later invalidated. Seven others remain formally undescribed since only genetic data is available and they have not been characterized on the basis of morphology.

“Our study recognizes the diversity of the genus and will help show, for example, how each species responds to certain processes, which ones are from a locality, and which ones have been introduced, among other things,” said Lawley, who is currently engaged in doctoral research at Griffith University in Australia.

“Our lab has specimens that live at 30 °C and others that live at 10 °C. We now know they’re not the same species. One of the developments from this study that are in progress is an investigation of their reproductive patterns to see how different species respond to environmental variations and how this will be influenced by factors associated with climate change,” said Morandini, who co-authored The World Atlas of Jellyfish, published in 2019.

The research is also supported by FAPESP via another project, whose principal investigator is Sérgio Stampar, a professor at São Paulo State University’s School of Sciences and Letters (FCL-UNESP) in Assis, and via a postdoctoral scholarship awarded to Maximiliano Maronna, a researcher at IB-USP. Both are co-authors of the PeerJ article.

The article “The importance of molecular characters when morphological variability hinders diagnosability: systematics of the moon jellyfish genus Aurelia (Cnidaria: Scyphozoa)” is at: https://peerj.com/articles/11954/.