"After studying 18 years of continuous records and studying the environmental factors we can say that more jellyfish are arriving each year," Professor Josep Maria Gili from Barcelona's Institute of Marine Sciences, told The Local.
The increase in numbers, according to Gili, can be attributed to the effects of a variety of man-made problems.
"The most important cause of the increased number of jellyfish, according to the scientific community, is the human impact on the oceans," said Gili.
"Overfishing, pollution and climate change have contributed to jellyfish multiplying in all the oceans.
"The most obvious cause is overfishing because lots of fish are the natural predators of the jellyfish and turtles also compete with the jellyfish for food (zooplankton). If the number of predators and competitors for food is decreasing it will simply increase the jellyfish numbers."
Increased temperatures and lack of rain are also important factors that can increase the numbers of jellyfish on beaches.
Last year, Spain experienced some of its highest ever temperatures, including three separate heatwaves, while meteorologists have predicted another summer of higher-than-usual temperatures.
But while the numbers of jellyfish have been on the increase, Gili confirmed that the creatures do not tend to hang around for too long.
"They will come for several episodes of a few days during the three summer months," he said.
"There have never been jellyfish on a beach for more than 15 days during the summer months and they usually appear for around three days."
Towns along Spain's northeastern coastline have developed special "jellyfish plans" such as the Jellyrisk project that are put in place when the creatures appear on the beaches. The plans, according to Gili, solve the problem of jellyfish "in 99 percent of cases".
"Coordination between local authorities, assistance of beach rescue teams and scientists has given excellent results on the Catalan coast," he said.
And what advice would Gili give to tourists worried about jellyfish along Spain's coasts?
"It is important to remember that jellyfish never bite swimmers, they sting when you come into contact with their tentacles.
"If there are jellyfish on the beach then it is better to swim in the pool that day and wait a day or two before going back to the beach,” he said.
Gili told The Local that the best protection against jellyfish stings is to use sunscreens "well and continuously".
What to do in case of a jellyfish sting
If you are stung by a jellyfish, Gili advises leaving the water immediately and looking for a lifeguard. If there are no lifeguards on the beach, wash the wound with salt water, never fresh water.
Cool the area down by applying ice for around five to ten minutes. You can also try wetting the wound with vinegar or baking soda dissolved in water.
Protect the area by using an antiseptic to avoid infections. If the pain continues, make sure you consult a doctor.
And Gili warns against the common myth that urinating on a jellyfish sting can help ease the pain.
"That is absolutely false," he told The Local.
"It could be effective for some fish bites but never for jellyfish."