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No invasion of Portuguese Man-of-War jellyfish in the Mediterranean this summer

The Joint Research Centre of the European Commission expects swimming in the Mediterranean to be safer this summer, as sightings of the dangerous Portuguese Man-of-War jellyfish decline.
 
Although the Portuguese Man-of-War (Physalia physalis) is not a native species in the Mediteranean basin, the region experienced a high number of swarms in 2010 that had dramatic consequences, including the first human fatality caused by a jellyfish sting (near Cagliari, Sardinia).

Despite the impact of jellyfish on coastal economic activity and the importance of the tourism industry for the Mediterranean region (accounting for 15% of global tourism), no scientific consensus has been achieved regarding the causes of this episode, JRC said.

"Based on analyses and simulations, the authors conclude that the 2010 event was the result of an unusual combination of meteorological and oceanographic conditions and not a permanent invasion," the centre said. 

The researchers found that the values during the winter of 2009-2010 of the North Atlantic Oscillation (NAO, a climatic phenomenon in the North Atlantic Ocean which has a strong effect on the wind and precipitation patterns of Europe) were among the most negative since recordings began, nearly 150 years ago. The intensity of westerly winds was between one and a half to four times higher than average. Theese unusually strong winds, along with the prevailing ocean currents, were likely to have moved the Physalia physalis population from the open Atlantic Ocean towards the mainland, through the Strait of Gibraltar, and into the Mediterranean basin. Field data and modelling simulations confirmed this hypothesis.

"Sightings of Physalia physalis have fallen dramatically since 2010, indicating that they will not pose a continuous problem along Mediterranean beaches and, unless the extreme negative values of the NAO become more frequent due to climate change, the 2010 exceptional occurrence of Physalia physalis is unlikely to reoccur on a regular basis," the centre said.

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