A plague of jellyfish along Europe's beaches has become the latest environmental hazard to be blamed on global warming.
Holidaymakers heading for Mediterranean beaches are being warned to prepare for an unprecedented invasion of the invertebrates whose sting can, in extreme cases, cause heart failure.
Oceana, which campaigns to protect and restore the world's oceans, attributes the rise in the number of jellyfish to a rise in water temperature because of climate change. It also highlights over-fishing of natural predators that feed on jellyfish, and pollution along the continent's coasts.
The group sent a research boat around Spain's coastal waters last month and concluded that many beaches are suffering an "invasion by this species".
After navigating the waters of the Mar Menor, Ricardo Aguilar, the director of research on Oceana's catamaran, said: "We have found jellyfish all over the Mediterranean, but in this area we've seen concentrations of more than 10 jellyfish per square metre. Wherever we look, there is practically nowhere without jellyfish."
Among the most notorious of jellyfish is the Portuguese man of war (Physalia physalis), whose stings can produce painful burns for bathers, and have even led to heart failure.
The Spanish researchers highlighted the prevalence of the purple jellyfish or mauve stinger (Pelagia noctiluca), whose stings can provoke severe swelling, burning pain and allergic reactions.
Other scientists have noticed the growing numbers of jellyfish. Gianluca Sara, the assistant professor of ecology and marine biology at the University of Palermo, plans to launch a research project on the issue in the autumn.
Dr Sara said: "I have no scientific data but, as an observer, there seems to be a huge increase along the Sicilian coast. I feel that temperature increase and over-fishing are related to this though, at the moment, this is only my feeling."
Jellyfish spend most of their lives in the open seas, because that is where the water tends to be more saline and warmer.
However, researchers believe they approach beaches when water near the coast, which is generally colder and less saline, stops acting as a barrier. That has happened in many places as there is less freshwater entering the sea from rivers because of the drought.
Oceana also blames the industrialised nature of modern fishing for reducing the number of predators that normally feed on jellyfish and keep their population under control.
Sometimes deliberately, sometimes accidentally through by-catches, fisherman have caught tuna, swordfish, moonfish, triggerfish and certain kinds of sea turtles - especially the leatherback turtle (Dermochelys coriacea), which is a major jellyfish predator.
Another cause of the invasion of the invertebrates may be the increase in nutrients in seawater due to contamination from land. Changing ocean tides could also be instrumental.
Advice from Oceana for those who are stung by jellyfish is to avoid rubbing the affected area with sand or with a towel. It says that freshwater should not be applied to the sting as the change in salinity could cause the stinging cells to burst and liberate the poison. It recommends using an ice pack in a plastic bag to avoid direct contact with the skin, unless the ice is made from seawater.