The growth of jellyfish populations throughout the world's oceans has been linked to global warming, overfishing of natural predators, and an increase in pollution that has depleted oxygen in coastal waters, say Spanish scientists.
Researchers at the Institute of Marine Sciences at the National Research Council in Barcelona have said the increase in jellyfish numbers from Spain to Australia, Japan and Hawaii is a sign of the declining health of the world's oceans.
“These jellyfish near shore are a message the sea is sending us saying, ‘Look how badly you are treating me,’” said Dr. Josep-María Gili, a leading jellyfish expert at the Council to the New York Times.
The scientists blame the overfishing of natural predators of the jellyfish (such as tuna and sharks), pollution, and a warming of the world's oceans partly due to global warming as the cause for the increase in numbers.
The National Science Foundation released a statement saying: “Human-caused stresses, including global warming and overfishing, are encouraging jellyfish surpluses in many tourist destinations and productive fisheries.”
The Foundation has listed Australia, the Gulf of Mexico, Hawaii, the Black Sea, Namibia, Britain, the Mediterranean, the Sea of Japan and the Yangtze estuary as the main problem areas.
“The problem on the beach is a social problem,” said Gili, referring to the problems of the numbers of jellyfish stinging swimmers in shallow waters. “We need to take care of it for our tourism industry. But the big problem is not on the beach. It’s what’s happening in the seas.”
Jellyfish are mostly harmless, though some deadly varieties do exist, and have been described by marine experts as the cockroaches of the sea thanks to being tough, durable and able to survive in damaged environments.