Overfishing has reduced competition for food, allowing jellyfish whose stings can cause pain and nausea, to thrive
Holidaymakers are being warned by the Foreign and Commonwealth Office to take local advice in several Mediterranean countries as jellyfish numbers rise along coastlines popular with tourists in Greece, Spain and Malta. Jellyfish numbers have been rising consistently in the Mediterranean, and researchers warn that the increase in numbers poses a hazard to swimmers, fishing and the marine environment.
The FCO said: "We have been alerted to large numbers of jellyfish in the Mediterranean this summer, especially in a number of key holiday destinations for UK tourists. We have updated our travel advice for a number of Mediterranean countries to reflect this issue."
Up to 150,000 people are treated for jellyfish stings in the Mediterranean each year. The worst-hit coastlines this summer have been in Greece, Spain, Sardinia, Sicily, Malta, Israel and Lebanon. The FCO recommends that swimmers speak to local authorities and follow their advice on where and when to swim.
Barcelona Institute of Marine Sciences researcher Josep María Gili told the Guardian in June that jellyfish represented a growing problem, both in the Mediterranean and across the world.
Climate change and over-fishing have been linked to the rise in numbers. Natural predators of the jellies, such as the ocean sunfish, have been declining in one of the most heavily exploited bodies of water on Earth.
Mediterranean JellyRisk programme co-ordianor Stefano Piraino told the BBC : "We are overfishing the oceans, which means we are catching all the big fish so the fish population is being reduced and we eliminate competitors and leave more food for the jellyfish."
The problem is further compounded by jellyfish feeding on the larvae of fish species. Scientists believe that human interventions that change the shape of the coastline and affect currents could also provide ideal breeding zones that encourage blooms.
There are no deadly jellyfish in the Mediterranean, but there are a number whose stings can cause pain and mild reactions. The mauve stinger (Pelagia noctiluca), which has been detected in vast swarms off the coast of Spain, can cause pain, burning, nausea and muscle cramps.
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