Overfishing in the Mediterranean has reduced the natural predators for jellyfish. The ocean sunfish, the main predator, is on the decline. Without control, the jellyfish then feed on fish larvae which makes the problem even worse. All that, combined with the changing coastline which provides ideal breeding zones, means that jellyfish numbers are on the increase.
Up to 150,000 people are treated for jellyfish stings in the Mediterranean each year and whilst the stings are not deadly they can cause pain and mild reactions. The mauve stinger, which is in vast swarms of the coast of Spain, can cause pain, burning, nausea and muscle cramps.