These days the Mar Menor is experiencing an explosion of the jellyfish Cotylorhiza tuberculata, popularly known as the fried egg. A video shows the impressive and beautiful images of an area of the lagoon teeming with specimens of this species, which is one of the least stinging species in existence. Isabel Rubio, a member of the Mar Menor Platform Pact, encountered the jellyfish three days ago while swimming with a partner as part of her regular check-ups to check on the condition of the lagoon. “I’m usually completely covered, but that day I was wearing a bathing suit in a hurry and the jellyfish were all around us, they didn’t harm us, it was an amazing feeling,” he says.
The yellowish-brown jellyfish with an orange bulge in the center started hatching about three weeks ago and are still growing. They range from a millimeter – when they hatch – to about 30 centimeters, maximum size a month or a month and a half after birth when they reach sexual maturity. They usually live between two and six months, which is why they are in the water during the summer, when tourism is more concentrated on the Spanish coasts. During the last excursion carried out on Wednesday, the highest concentration was found in the north-central area of the lagoon, while the value was very low in the southern area, says Emilio María Dolores, spokesman for the scientific advisory board of the small sea. Jellyfish move with the currents and winds, and this species also has a good ability to propel themselves.
Depending on the evolution of the jellyfish (amount and movements) in the coming days, the Murcia government will take action if necessary. Some communities have requested that nets be placed to protect beaches, but for the alternative to be considered, they would need to formally request it, an executive branch spokesman said. María Dolores advises against it because other organisms cling to it, algae multiply, water exchange is lower and can affect bathing quality, and handling it can affect sensitive species such as seahorses.
Specimens of Cotylorhiza tuberculata in the Mediterranean. Claudio Alvarez
The Mar Menor has a serious problem of eutrophication in its waters due to the large amount of nitrates – from fertilizers – entering the lagoon mainly from agricultural activities. This imbalance has resulted in significant mortality of fish and crustaceans due to the lack or lack of oxygen in the water since the lagoon turned into a green soup in 2016. Does this circumstance affect the growth of jellyfish? The more nitrates there are, the more feed is produced for these animals. So this is a factor to consider, but with a limit. In this case, “there is no direct connection because [esta especie denominada] Fried eggs require some algae that live inside the jellyfish, which in turn require some transparency in the water to perform photosynthesis.” For this reason, if the Mar Menor were in a very bad state, the jellyfish would not evolve.
This does not mean that the lagoon has regained its balance. The entry of nitrates continues along the Rambla del Albujón. “Unfortunately, it’s a recurring theme, it’s the crab of the Mar Menor,” laments María Dolores. This Friday the flow is 208 liters per second. “Nothing was supposed to go in, but we have normalized that this boulevard will become a river fed by the drainage networks of the Campo de Cartagena farms,” he adds. Nevertheless, the situation is better than on the same dates in other years, although algae removal continues. Chlorophyll levels are 0.35 milligrams per liter, the lowest since 2016 when the lagoon collapsed.
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The reason for this improvement is not that the origin of the problem has been addressed, but rather meteorological issues: it has rained less and therefore less water has entered the lagoon due to runoff of nitrogen (from fertilizers). Last year, from January 1st to this date, the Mar Menor had received 6 cubic hectometres, and this year, over the same period, it has dropped to 2.7. “In 2022 it rained a lot in March and April and especially near the Mar Menor. This year, in May, the water dropped, but in the upper part of the basin, so the volume that reaches the lagoon is lower,” the Advisory Committee director clarifies.
Josep María Gili, a CSIC research professor, has been studying jellyfish for more than 40 years and believes the return of fried eggs is “good news for the Mar Menor”. “If there are no jellyfish, it’s because the conditions are so catastrophic that even they can’t survive,” he specifies. In the Mar Menor there was a stable population of jellyfish in summer and another in winter, the Aurelia aurita, but this dies out before the warm months. “Fried egg is a jellyfish that, like all coastal jellyfish, goes through a polyp phase that attaches to the sea floor and can remain there for decades if not eaten,” he explains. Those born now are descended from these polyps, which may not have thrived earlier due to the poor conditions in the lagoon. “Fifteen years ago we managed to catch around 2,000 tons of this species in the Mar Menor with the fishermen’s nets,” he says. A system that might now be salvaged without leaving the debris stranded on the beach, he warns.
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