Jellyfish in a Coalmine

From this week's New York Times article, Stinging Tentacles Offer Hint of Oceans' Decline:

“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, who has studied them at the Institute of Marine Sciences of the Spanish National Research Council in Barcelona for more than 20 years.

The explosion of jellyfish populations, scientists say, reflects a combination of severe overfishing of natural predators, like tuna, sharks and swordfish; rising sea temperatures caused in part by global warming; and pollution that has depleted oxygen levels in coastal shallows.