Presence of medusae of the species Cassiopea andromeda is confirmed in Brazil

Analysis suggests the species migrated from the Red Sea to the Americas during the age of discovery some 500 years ago.

By Karina Toledo  |  Agência FAPESP – Its striking name was inspired by two women in Greek mythology: Cassiopeia, the vain and boastful queen of Ethiopia who provoked the wrath of the sea-nymph Nereids, and her daughter Andromeda, who was sacrificed to a sea monster to appease the gods.

Cassiopea andromeda is quite unlike other species of jellyfish, which are always swimming in search of food and mates. It is so bashful that it spends most of its life upside down in the same place. However, it is demanding: the waters it calls home must be calm, shallow, warm and translucent.

The species originated in the Red Sea, and until recently, scientists thought it did not occur in Brazilian coastal waters, which did not provide the right habitat for its survival. However, now its presence here in the adult form, as a medusa, has been confirmed for the first time, in a study supported by FAPESP and published in the Journal of the Marine Biological Association of the United Kingdom.

Genetic analyses described in the paper suggest that C. andromeda has lived in Brazilian waters for much longer than might be imagined. One hypothesis is that it came to the Americas in the age of discovery, when European ships criss-crossed the planet in search of the new world. Its first home in the region was probably Florida and the Caribbean. Later on, intense shipping traffic up and down the Atlantic likely brought it to the coast of South America.

“Our theory is that the species was carried to Brazil in the ballast or attached to the hull of a sixteenth-century ship, probably in polyp form,” said Sérgio Nascimento Stampar, a professor at São Paulo State University (UNESP) in Assis and a co-author of the paper.

Like many jellyfish species, C. andromeda occurs in two body forms, as sessile (non-motile) polyps and free-swimming medusae, he explained. Adult medusae reproduce sexually and give rise to polyps, which do not move voluntarily and attach themselves to rocks, shells or other solid structures. Polyps are 5 mm long at most and are considered immortal by scientists.

“Polyps reproduce asexually by budding, giving rise to new, genetically identical polyps or, if the environmental conditions are right, producing medusae. In the adult phase, the animal can reach between 30 cm and 40 cm in diameter, the size of a pizza,” Stampar said.

Polyps of C. andromeda were sighted in Brazil in 1999 at the University of São Paulo’s Marine Biology Center (CEBIMAR-USP). “We didn’t expect to find the adult form on our coast because it prefers conditions like those prevailing in the Caribbean, especially clear water that allows sunlight to penetrate,” Stampar said. “This dependency on solar energy is due to the fact that the species lives in a symbiotic relationship with photosynthetic dinoflagellate algae, which transfer part of the carbon they produce to the medusae in exchange for nutrients and shelter.”

In addition to consuming part of the energy produced by the symbiotic algae, C. andromeda feeds on small animals that inhabit the sediment on the seafloor. This is why it feeds upside down with its bell resting on the floor, pulsing to force zooplankton into its mouth openings.

Professor André Carrara Morandini, Head of the Zoology Department in the same university’s Bioscience Institute (IB-USP) and lead author of the paper, recalled having received photographs of a population of unusual jellyfish that had appeared in 2008 in the Itajuru Channel in Cabo Frio, Rio de Janeiro State.

“At the time, I was working at the Federal University of Rio de Janeiro (UFRJ) near Cabo Frio and was asked to help identify the species, which was then unknown. We knew it belonged to the genus Cassiopea, but there are 12 species in the genus, and we were unable to decide which one of these they matched,” Morandini said.

Genetic analysis confirmed that they were C. andromeda. Morandini’s group compared samples collected in Brazil with data from public databases such as GenBank and found that the genotype was identical to that of C. andromeda specimens from the Caribbean and Red Sea.

“We discussed how these jellyfish could have traveled over such huge distances and concluded that they had come with the explorers’ ships during the age of discovery,” Morandini said. “Molecular dating models that compute a species’ mutation rate enabled us to estimate when this migration occurred. However, we still don’t know whether it migrated gradually from the Caribbean to Brazil because a second introduction to the Americas may have occurred independently.”

Sudden disappearance

For some reason that the researchers have yet to discover, the population of medusae found in Cabo Frio developed intensely in 2008-09 and then declined. At its peak, they counted more than 2,000 individuals in an area of 200 square meters. They all disappeared in 2012-13.

The polyps are still there, however, and polyps of C. andromeda can be found in various parts of the Brazilian coast.

“The sudden disappearance of the medusae is a sign that the species isn’t native but introduced or invasive,” Morandini said. “Another sign is that all the individuals in this Cabo Frio population were male.”

The paper notes the environmental risk represented by invasive species, which may dominate an area owing to the absence of natural predators, jeopardizing the survival of other species and creating an ecological imbalance.

“In some parts of the world, such as Japan, the jellyfish population explosion is a serious problem,” Stampar said. “They’re venomous and can kill fish and other marine organisms with which they come into contact, so they’re a threat to fishing and aquaculture. C. andromeda is a non-native species in Brazil, so this could happen at any time if it adapts to the region.”

However, Morandini believes the risk is small. “The species might cause an imbalance in a closed area like a bay or lagoon,” he said. “But its motility is very limited, and it’s unlikely to spread very much. I don’t foresee a major impact on the environment to the extent that it could be a hazard to humans.”

The research behind the published paper was conducted as part of a Thematic Project, for which the principal investigator is Antonio Carlos Marques, also a professor at IB-USP, under the auspices of FAPESP’s Research Program on Biodiversity Characterization, Conservation, Restoration & Sustainable Use (BIOTA-FAPESP).

The article, “All non-indigenous species were introduced recently? The case study of Cassiopea (Cnidaria: Scyphozoa) in Brazilian waters” (doi: 10.1017/S0025315416000400) can be read at journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10266270&fileId=S0025315416000400.