Greece jellyfish warning for UK tourists
The UK Foreign Office has updated its travel advice for Greece, warning that jellyfish blooms have been reported and for people to heed local advice.
Officials have already issued warnings about jellyfish in Mediterranean coastal waters for France and Italy.
But local marine biologists said this year's increase was "no different" from other years and that the blooms consisted of non-stinging species.
They added that they were monitoring the situation very closely.
A Foreign Office spokeswoman told BBC News: "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."
She added that the Foreign Office aimed to keep its advice "as informative and useful for visitors as possible".
However, Stefano Piraino - project co-ordinator of the Mediterranean JellyRisk programme - said there was no need for tourists to be unduly concerned.
"Of course, as in any other ocean or sea in the world, there might be some problems," he said.
"In the Mediterranean, we are lucky and do not have deadly [jellyfish]."
But he did acknowledge: "We are experiencing, as in many other places around the world, an increase in jellyfish."
Prof Piraino, a marine biologist at the University of Salento in southern Italy, said the JellyRisk programme - also involving researchers from Spain, Tunisia and Malta - was set up because there was growing concern about the impact of increasing number of jellyfish on human activities in the region, such as fishing as well as tourism.
He told BBC News that the programme's main focus was on a citizen science campaign.
"This is a very important tool," Prof Piraino observed.
"We have, since 2009, used this approach where we are asking tourists, sailors, fishermen, divers - all the people that are in the sea - to send information about the presence of jellyfish."
The team have developed a smartphone application that not only allows people to send information, but also receive details about the abundance of jellyfish in their area.
The app also provides scientifically sound information about how to treat stings because the venom of jellyfish varies according to the species that inflicted the injury.
"We have collated scientific evidence and results from clinical trials, which we have reviewed so we can now, through the app and printed material, offer advice on the treatment of stings," he explained.
The team will also install anti-jellyfish nets at a number of popular beaches in order to assess their effectiveness.
Prof Piraino said it was difficult to pinpoint a single cause for the increase in the abundance of jellyfish.
"This is a result of many different causes. These can be different from site to site," he said.
"Generally, there is evidence that there is an increased abundance because of an increase in sea surface temperature.
"This is coupled with other things, such as the fact that we are changing the coastal marine environment."
One example he cited was the construction of artificial reefs for flood defences, which used a material favoured by jellyfish.
He added that this has been observed more often in other European bodies of water, such as the North Sea.
"This places a hard substrate in the sea, which is the preferred substrate for the larvae stage of jellyfish.
Overfishing was another contributing factor, he added.
"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."
A recent report published by the UN Food and Agriculture Organization (FAO) concluded that the increasing number of jellyfish was creating a "vicious cycle" because the jellyfish were also feeding on the eggs and larvae of commercially important fish species.
In June, marine researchers gathered in Japan for the fourth International Jellyfish Bloom Symposium to share research on the global problem.
According to the FAO report, some experts have warned that, if the trend continued unabated, jellyfish could supplant fish in the world's oceans, triggering a "global regime shift from a fish to a jellyfish ocean".
Prof Piraino offered a solution, saying that people had to "learn to love jellyfish".
"The Chinese have been eating jellyfish for millennia," he said.
"Now there is documented evidence that non-stinging jellyfish in the Mediterranean can be eaten - they are full of antioxidants and they provide molecules that can be used in the pharmaceutical or cosmetic industries.
"Therefore the creatures should be viewed as a resource rather than a pest."