Experts analyze the effects of their presence at sea
They control the ecological balance and help the transparency of the waters
summer lands on the minor sea (Murcia) and vigilance over the salt lagoon is being extreme both by scientists and environmental activists who seek to take the pulse of an ecosystem loaded with nutrients. The member of the organization Pact for the Mar Menor, Isabel Rubio, is one of those faithful eyes of the lagoon that checks every corner checking that everything is going according to plan or that something is not working well. In her last dives, this retired teacher and defender of the lagoon has been surprised like never before by the large presence of jellyfish Cotylorhiza tuberculatabetter known as ‘fried egg’.
The ‘birth’ of these specimens occurred at the beginning of May, according to a report from the General Directorate of the Mar Menor dated that same month. Already then a “considerable number” of ephyra of jellyfishthe juvenile phase of these species, and specifically of the Cotylorhiza in the environment of the internal islands of the lagoon. “In principle, the number of ephyra is large, which allows us to foresee a large number of specimens,” they concluded then.
At the gates of the summer campaign, the hotel sector of the Mar Menor hopes to achieve better figures than past seasons, but the state of the waters influences the decision of potential tourists. With the summer comes the increase in temperatures which, together with the dragging of nutrient-laden sediments as a result of the last rains, cause a climate of concern around the lagoon, as has been the case since 2016, the year of the great ‘green soup’.
For this reason, the Pact for the Mar Menor demanded on Tuesday both the Ministry of the Environment and the Spanish Institute of Oceanography a scientific explanation, but clear and understandable, of two phenomena that are taking place in the salty lagoon and that they are causing, they say , “social alarm”. Firstly, that ‘bloom’ that lives the ecosystem of the ‘fried egg’ jellyfish and, secondly, the white spot of the Mar Menor located in the central-western area of the lagoon.
How is the ‘fried egg’ jellyfish
The organization that defends the interests of the Mar Menor points out that this species of jellyfish is colonizing a large part of the water column, as shown in the photos of Rubio and his companion Francisca Alcaraz. They both remember that This species is not dangerous or causes problems, but they ask for caution for children with sensitive skin. The organization adds that both issues have caused “social alarm” and they want to avoid negative impacts on hotel reservations in the Mar Menor.
The latest reports from the University of Murcia and the Community Fisheries Service suggest that the populations of the ‘fried egg’ jellyfish “will be high” this summer, but they will make it possible to control “better the trophic chain of the lagoon and will contribute to a greater transparency of the waters”.
The experts determine that its population has recovered and reaches the previous levels that were registered before the ‘green soup’ of 2016. That same year “they had practically disappeared, or were at low levels, as a consequence of the darkening of the column of water that prevented the light from reaching the seabed and caused the death of the jellyfish”.
Jellyfish populations in the Mar Menor are not something new for professionals from the University of Murcia (UMU) and the Ministry of Fisheries, since since the mid-1990s their presence has been constant, and “during some periods more accused”. The ‘fried egg’ has a life cycle of between 2 and 6 months and is not stinging. “This species has mechanisms that cause its multiplication to not totally depend on the availability of nutrients (phytoplankton and zooplankton) in the water.”
The lagoon has always had a kind of winter called Aurelia auritaknown by fishermen as ‘bad water’ that closes its cycle at the beginning of summer, Therefore, its presence during the summer season is very low, practically non-existent from the first days of July, depending on the water temperature.
Other jellyfish present in the lagoon are the Rhizostoma pulmowhich has an urticating character, and the Phyllorhiza punctataof recent appearance and morphologically similar to the Rhizostoma pulmo, but with a dotted on the bell of the jellyfish. They have been detected and follow-up is being done to assess their situation.
A symptom of the ecosystem
They have always been in the lagoon and their presence is a symptom of the poor state of the water. For the marine biologist from the Spanish Institute of Oceanography (IEO), Miguel Vivasthe populations of the Jellyfish ‘fried egg’ is a consequence of “imbalance and nutrient input” that the Mar Menor suffers. If the conditions are propitious, he points out, this proliferation of the species at the gates of summer is common: «I do not see anything abnormal in what is happening. It’s nothing extraordinary.”
The ‘bloom’ of Cotylorhiza tuberculata is a response to “environmental conditions” that favor its stay in the lagoon: “We have known this for a long time.” Its presence is more common in the southern area of the lagoon due to the currents and the entry of nutrient-laden water from the Albujón boulevard.
“They are the most eutrophic areas”, where they can have more food. Its filtering capacity makes it possible to assign an apparently positive role in the lagoon, remarks the biologist, but he believes that its effects on the Mar Menor should be studied in more depth.
“They are removing nitrogen from the water column, they are taking nutrients. But at the end of the summer they die and everything they have taken returns to the system »Vivas explains. However, he adds that “we don’t know to what extent” the function they perform may be beneficial. In a personal evaluation, remember that the presence of this jellyfish can be detrimental to the seahorse when it is in a very young phase and they float in the water, at which time they would be more vulnerable.
Vivas believes, in his opinion, that not installing anti-medusa nets is a good option, since it is a more aesthetic than functional measure. “The green egg is hooked to the nets and fish such as sea bass or sole remain trapped.”
Unknown origin
Regarding the White stain, the last report from the IEO in May warns of changes in the hydrographic structure of the stain after being unaltered for months. “The turbidity values in this whitish body of water are not as high as those of April, probably because the contributions of continental waters associated with heavy rains have altered the structure, composition and distribution of said body of water.”
However, the Oceanográfico researchers point out that the bleaching is related to the biological activity of the planktonic community of the lagoon but “it has not been previously observed in the Mar Menor and its properties, dynamics and possible consequences are still not clear.” in the lagoon ecosystem. New samples are being tested for this.”
The spokesman for the Scientific Committee of the Mar Menor, Emilio Maria DoloresFor his part, he recalled that this whitish area “is not a new image and is due to the continuous resuspension of non-soluble particulate matter that has reached that area as a result of runoff and leachate. This area is usually the one with the highest concentration of nutrients. The size and shape of the stain depends on the prevailing currents and winds.”
The spokesperson added that “the current nutrient levels fall within the parameters set by the regulations, except in two stations in front of the Albujón boulevard, and the amount of water that has entered has been significantly less than in 2022, although still excessive & rdquor ;.
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