In the summer light, concerns over the Mar Menor’s salt lagoon are shared by scientists and environmentalists who aim to protect a nutrient-rich ecosystem. A longtime member of the Mar Menor Agreement, Isabel Rubio, watches the lagoon closely, ensuring that plans stay on track and that any problems are spotted early. Rubio, a retired teacher and devoted defender of the lagoon, faced a moment of surprise during her final dives. The Cotylorhiza tuberculata jellyfish, commonly called the fried egg, drew attention with its striking appearance.
The early May report from the Mar Menor Headquarters noted the birth of these specimens. At that time, juvenile ephyrae jellyfish, especially Cotylorhiza, had been found among the inland islands of the lagoon. Officials observed that the number of young jellyfish was already large, which signaled a potential rise in adult populations later in the season (University of Murcia, cited by local authorities).
As the summer season approached, hotel operators in the Mar Menor hoped for stronger business than in previous years, yet the state of the water continues to influence travelers’ choices. With rising summer temperatures and sediment carried by recent rains, nutrient-laden runoff is creating a troubling climate around the lagoon, a pattern seen since 2016 when the water earned the nickname green soup.
Consequently, the Mar Menor Agreement called on the Environment Ministry and the Spanish Oceanographic Institute to provide a clear, scientifically grounded explanation for two phenomena affecting the salty lagoon. They described a social alert tied to a bloom of the fried egg jellyfish and a white speck forming in the midwestern area of the lagoon.
How about fried egg jellyfish?
The organization representing the lagoon’s interests notes that this jellyfish species spans a large portion of the water column, a fact visible in Rubio’s photos with her colleague Francisca Alcaraz. They recall that this strain is not dangerous, though it requires caution for children with sensitive skin. The group emphasizes that both issues generate social concern and they want to safeguard tourism for the Mar Menor.
Recent findings from the University of Murcia and the Community Fisheries Service indicate the fried egg jellyfish populations will likely be high this summer. They suggest these blooms can help regulate the lagoon’s trophic chain and improve water transparency. Experts observe a recovery toward population levels seen before the green soup events in 2016. The presence of jellyfish also reflects how nutrients influence light penetration and seafloor health, sometimes limiting photosynthesis in the water column.
Jellyfish populations in the Mar Menor are not a new topic for researchers at the University of Murcia and the Ministry of Fisheries. Their presence has been steady since the mid-1990s and has at times been linked to ecological pressure. The fried egg jellyfish completes a life cycle of two to six months and does not bite. Its reproduction is closely tied to the availability of nutrients such as phytoplankton and zooplankton in the water.
The lagoon has long experienced seasonal shifts. Known among fishermen for a period as bad water, Aurelia aurita completes its cycle early in summer, making its summer presence minimal. Other jellyfish spotted in the lagoon include Rhizostoma pulmo, which can sting, and Phyllorhiza punctata, a species that has appeared more recently and bears distinctive marks on its bell. These species are being tracked to assess their status and impact.
A symptom of the ecosystem
Jellyfish have always inhabited the lagoon, serving as a sign of the water’s stress. A marine biologist from the Spanish Institute of Oceanography notes that the fried egg jellyfish population results from an imbalance and nutrient input affecting the Mar Menor. If conditions favor it, these jellyfish can multiply rapidly in summer, though that may not be unusual in the eyes of some scientists.
The fried egg’s bloom responds to environmental factors that support its presence in the lagoon. The southern part of the lagoon often sees higher concentrations due to currents and nutrient-laden water flowing from adjacent channels, creating more food for these jellyfish. While their filtering ability might have positive ecological effects, experts urge caution and further study on how their abundance affects other species in the Mar Menor.
Experts note that the jellyfish help remove nitrogen and other nutrients from the water, but they also die later in the season, returning nutrients to the system. Opinions vary on the extent of their positive role, and some warn that the jellyfish may pose risks to very young sea horses exposed to their presence.
One proposed measure favors natural conditions over nets, which serve simply as aesthetics. Nets can trap larger fish and disrupt the ecological balance while doing little to control the jellyfish population itself.
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Recent white-spot findings from the IEO highlight changes in the lagoon’s hydrographic structure that had remained stable for months. Turbidity in this whitish water body has decreased since April, likely due to changes in runoff and rainfall patterns that alter water composition and distribution. Yet researchers caution that while bleaching correlates with planktonic activity, it is not observed before in the Mar Menor, and the characteristics, dynamics, and consequences remain unclear. New samples are being tested to better understand these developments (IEO investigations).
Spokesperson for the Mar Menor Scientific Committee notes that the whitish area is not new and results from continuous resuspension of insoluble matter that reaches the area through runoff and leachate. This zone typically shows the highest nutrient concentration. The extent of the spot depends on currents and winds.
The current nutrient levels fall within regulatory limits, except for two stations in front of the Albujón boulevard where water inflow remains higher than in 2022, though still excessive according to monitoring data (IEO commentary).