Over the last two weeks, a dozen towns on the Costa Brava and Maresme have recorded the presence of large quantities of jellyfish, both in the water and on the beaches, carried by sea currents and storms. 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 multitudinous and has surprised to neighbors and visitors.
The first invasion of jellyfish observed especially on the Costa Brava is “relatively common although it arrives somewhat earlier than in other years, probably due to the sea conditions, the temperature and the lack of rain in recent months”, explains Josep Maria Gili. , biologist and CSIC research professor at the Institut de Ciències del Mar (ICM) specialized in the study of jellyfish.
Sergi Corral, botanist and meteorological observer, explains from his own experience that in the case of l'Escala, "the first large accumulation was of velellas 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 velella reach the coast sooner 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, large schools or swarms 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,” Josep Maria Gili tells La Vanguardia. Water temperature and drought can alter the natural barrier that exists on the coast, which limits the arrival of jellyfish to the beaches, says this expert.
The storms of recent weeks could also have influenced the spring dynamics of the jellyfish, but “we do not have enough data to determine it,” 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 lack of economic resources, after the pandemic and has not been able to recover, so we do not have data exhaustive about what is happening now with 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. Thermophilic species move to increasingly hot areas and temperate species are cornered in the coldest parts of the Mediterranean," explains marine biologist from the Institute of Marine Sciences (ICM-CSIC) Paula López Sendino, who adds: " It also causes phenological changes in reproduction. "Posidonia oceanica, an endemic plant and emblem of the Mediterranean, blooms, which corresponds to the sexual reproduction phase, every 10 years, but the increase in temperature causes the process to accelerate."
With the data available, Josep Maria Gili points out that the observed arrival of jellyfish is within the norm, but moving forward a few weeks. The high temperatures, the lack of rain and, more generally, 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, therefore, a greater vigilance to prevent impacts, for example from bites on bathers.”
All the factors accumulated this year, with the early arrival of coastal jellyfish and the foreseeable arrival of open sea species in summer, suggest “a tough season,” concludes Josep Maria Gili.
