A dozen towns on the Costa Brava and the Maresme have registered the presence of large quantities of jellyfish, both in the water and on the beaches, washed up by sea currents and storms in the last two weeks. In some areas, such as the bay of Roses and l'Escala (Alt Empordà) the accumulation of specimens of velella or sea sail (hydrozoan, Velella velella) and luminescent jellyfish or sea carnation (Pelagia noctiluca) has been massive and has surprised neighbors and visitors.
The first invasion of jellyfish observed especially on the Costa Brava is "relatively common, although it arrives a little earlier than other years, probably due to the conditions of the sea, the temperature and the lack of rain in recent months", he explains Josep Maria Gili, researcher at the Institute of Marine Sciences specializing in the study of jellyfish.
Sergi Corral, botanist and weather observer, explains from his own experience in the case of l'Escala, "the first big accumulation was of barnacles two weeks ago and last week the luminescent jellyfish arrived".
From the point of view of the marine environment, Corral considers that the presence of jellyfish "is common in the spring cycle and is good news, because they are part of the food chain, they serve as food for many other species".
"The barnacles reach the coast earlier because they are organisms - colonies of polyps, they are not actually jellyfish - that live in surface waters and are moved more quickly towards the coast, while the Pelagia nocticula proliferate more in the open sea", says Josep Maria Gili
Although the presence of both species in early spring is normal on our coasts, the large shoals or shoals may have been facilitated by several factors. "If the temperature of the sea water on the coast is similar to that of the open sea, it is easier for the jellyfish to reach the coast; on the other hand, due to the lack of rain, less fresh water reaches the coast", says Josep Maria Gili in La Vanguardia. The water temperature and the drought can alter the natural barrier on the coast, which limits the arrival of jellyfish on the beaches, this expert points out.
The storms of the last few weeks could also have influenced the spring dynamics of the jellyfish, but "we don't have enough data to determine that", explains Gili. In fact, this expert from the Institute of Marine Sciences recalls that the scientific study of the presence of jellyfish "was practically paralyzed, due to a lack of financial resources, after the pandemic, and has not been able to recover, because which we do not have comprehensive data on what is happening now with the jellyfish on our coast”.
"Climate change can favor the proliferation of species such as jellyfish, or it can cause changes in the distribution of fish. The thermophilic species move to increasingly hotter areas and the temperate ones remain cornered in the coldest parts of the Mediterranean", explains the marine biologist of the Institute of Marine Sciences (ICM-CSIC) Paula López Sendino, who adds: " It also causes phenological changes in reproduction. The oceanic posidonia, an endemic plant and emblem of the Mediterranean, blooms, which corresponds to the phase of sexual reproduction, every ten years, but the increase in temperature speeds up the process”.
With the available data, Josep Maria Gili points out that the observed arrival of jellyfish is within what is usual, but it is a few weeks ahead. The high temperatures, the lack of rain and, in a more general way, the disappearance of natural predators and the existence of infrastructure on the coast are factors that "make us expect a greater presence of jellyfish on our coast and, to therefore, greater vigilance is needed to prevent impacts, for example, from bites on bathers".
All the factors accumulated this year, with the early arrival of coastal jellyfish and the predictable arrival of open sea species in the summer, make us think of "a tough season", concludes Josep Maria Gili.
