Explosion of ‘Fried Egg’ Jellyfish in Mar Menor

by Lorraine Williamson
fried egg jellyfish at Mar Menor

Mar Menor is currently experiencing an explosion of Cotylorhiza tuberculate jellyfish. They are popularly known as ‘fried egg’ jellyfish. A video showcases the breathtaking and mesmerising images of an area in the lagoon teeming with these jellyfish, which are among the least stingy species.  

These jellyfish, with their yellowish-brown colour and a central orange protrusion, began to emerge about three weeks ago and are still growing. They range in size from one millimetre at birth to a maximum of around 30 centimetres after one to one and a half months when they reach sexual maturity. They typically live for two to six months, making their presence more prominent during the summer season when tourism is at its peak on Spanish coasts.  

During the latest survey conducted on Wednesday, the highest concentration was detected in the central-northern area of the lagoon, while the level was very low in the southern area, according to Emilio María Dolores, spokesperson for the Mar Menor scientific advisory committee. Jellyfish are carried by currents and winds, and this particular species also exhibits good self-mobility. 

Request for safety nets 

Depending on the evolution of the jellyfish population (quantity and movements) in the coming days, the Government of Murcia will take necessary measures if required. Some municipalities have requested the installation of nets to protect the beaches. However, environmentalists advise against the use of nets because they tend to accumulate other organisms, promote algae growth, reduce water exchange, and potentially impact water quality for swimming. Moreover, handling the nets could also affect delicate species such as seahorses. 

Mar Menor has been grappling with a severe eutrophication problem in its waters due to high levels of nitrates from fertilisers that seep into the lagoon, primarily from agricultural activities. This imbalance has led to significant fish and crustacean mortality due to decreased or insufficient oxygen levels in the water since the lagoon turned green in 2016.  

Also see: Unusual whitish body of water in Mar Menor is under investigation 

Does this circumstance influence the jellyfish boom? The higher the nitrate levels, the more food is available for these creatures, so it is a factor to consider, but with limitations. In this case, “there is no direct relationship because this species, known as the ‘fried egg’ jellyfish, requires certain algae that live within the jellyfish, which in turn need a certain level of water transparency to carry out photosynthesis.” Therefore, if the conditions in Mar Menor were extremely poor, the jellyfish would not thrive. 

However, this does not imply that the lagoon has regained its balance. Nitrate influx continues through the Albujón riverbed. “Unfortunately, it’s a recurring issue, the cancer of Mar Menor,” lament the spokesperson of the platform Pact for Mar Menor. Currently, the flow is at 208 litres per second. “There shouldn’t be any inflow, but we have normalised the transformation of this riverbed into a river, fed by the drainage networks of Campo de Cartagena’s farms,” she adds.  

Cogesa Expats

Nevertheless, the situation is better than in previous years at the same time, although algae are still being removed. The chlorophyll level is 0.35 milligrams per litre, the lowest value since 2016 when the lagoon experienced a collapse. 

Also read: Jellyfish in Spain: A guide to seasonal encounters and safety tips 

The improvement in water quality, however, is not due to addressing the root cause of the problem but rather to meteorological factors: less rainfall resulting in reduced water inflow to the lagoon carrying nitrogen from fertilisers. Last year, from January 1st to this period, Mar Menor received 6 cubic hectometers of water, whereas this year, it has dropped to 2.7. “In 2022, there was a lot of rain in March and April, especially near Mar Menor. This year, water fell in May, but in the upper part of the basin, so the volume reaching the lagoon is smaller,” clarifies the director of the advisory committee. 

Return of the ‘fried egg’ jellyfish is a positive sign for Mar Menor 

Josep María Gili, a research professor at CSIC, has been studying jellyfish for over 40 years and considers the return of the ‘fried egg’ jellyfish a positive sign for Mar Menor. “If there are no jellyfish, it means the conditions are so disastrous that even they cannot survive,” he explains.  

Mar Menor used to have a stable population of jellyfish in summer and another in winter, the Aurelia aurita, which dies before the warmer months. “The ‘fried egg’ jellyfish, like other coastal jellyfish, goes through a polyp phase that attaches to the seafloor, where they can remain for decades if not consumed,” he elaborates. The jellyfish currently emerging are offspring of those polyps, which perhaps did not prosper due to the lagoon’s poor conditions.  

“Fifteen years ago, we removed around 2,000 tons of this species from Mar Menor using fishermen’s nets,” he comments. This system could potentially be reinstated now, with the caution of not leaving remnants on the beach. 

What do I do if it bites? 

The bite of a ‘fried egg’ jellyfish should not be a concern due to its low level of toxicity. However, yes, it can cause irritation and burning in the affected skin. The Ministry of Ecological Transition recommends, in the event of a bite, washing the affected area with seawater, never with fresh water, ammonia, vinegar or urine.  

Also read: Carefree swimming without jellyfish in Spain: do the check 

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