After an entertaining time seeking out octopus and cuttlefish among the rocky architecture at the bottom of the Mediterranean sea, my air ran low and it was time to surface. I noticed my fellow divers rising above me were adopting a strange hunched posture, tucking their hands into their armpits and bowing their heads low.
As I rose to a couple of metres below the surface, I saw the problem too late: the shallow water was carpeted with mauve stinger jellyfish (Pelagia noctiluca). There was no avoiding it, reaching the surface meant I had to swim through the flames of stingers.
Onshore, a diver offered to help soothe the burning lashes across my neck, forehead and hands. "I could pee on them," he suggested. I declined.
Locals told me the carpet of jellyfish, known as a bloom, was not an isolated case. My dive instructor said he had seen massive blooms off the coast of Gozo every year since 2000. But never before then.
In fact, huge annual jellyfish blooms have been cropping up not just across the Mediterranean, but also the Black Sea, the Gulf of Mexico, and the Yellow and Japan Seas. Is this a bizarre blip in the continually changing balance of oceanic life, or the beginnings of a new state change in marine diversity?
Or in other words: in the Anthropocene, will the seas be filled with slime?
If they are, we face some serious problems. Last year alone, nuclear power plants in Scotland, Japan, Israel and Florida, and also a desalination plant in Israel, were forced to shutdown because jellyfish were clogging the water inlets. The entire Irish salmon industry was wiped out in 2007 after a plague of billions of mauve stingers – covering an area of 10 sq miles (26 sq km) and 35ft (11m) deep – attacked the fish cages. Two years later, a fish farm in Tunisia lost a year's production of sea bream and sea bass after jellyfish invasions.
Perhaps the most extraordinary blooms have been those occurring in waters off Japan. There, refrigerator-sized gelatinous monsters called Nomuras, weighing 485lb (220 kg) and measuring 6.5ft (2m) in diameter, have swarmed the Japan Sea annually since 2002, clogging fishing nets, overturning trawlers and devastating coastal livelihoods. These assaults have cost the Japanese fisheries industry billions of yen in losses.
Marine ecologists are warning of worse to come, and pointing the tentacle of blame at us. Some researchers fear that human changes to the marine environment may be leading to a tipping point in which jellyfish will rule the oceans, much as they did hundreds of millions of years ago in pre-Cambrian times. In 2009, Australian marine scientist Anthony Richardson and his colleagues published a research paper entitled The jellyfish joyride, in which they warn that if we do not act to curb current blooms, we will experience runaway populations that will cause open oceanic ecosystems to flip from ones dominated by fish biodiversity to ones dominated by jellyfish.
The problem is that no one really knows what causes the blooms. Some believe that population explosions result from overfishing of their dining competitors and predators, which include more than 100 species of fish, and animals such as turtles. However, other researchers point out that overfishing also hits jellyfish by reducing their food availability.
Either way, what is clear is that jellyfish are simply better prepared than other marine life for many of the ways humans are changing the ocean environment, such as warmer temperatures, salinity changes, ocean acidification and pollution. In this sense, humans might be jellyfishes’ best friend.
For instance, pollution can cause algal blooms that reduce the water's oxygen content. This hits muscular swimmers like fish hard, but jellyfish can cope far better with these conditions.