Of all the oceans’ predators, jellyfish have the least … of everything: With no teeth, fins or brains, they catch only whatever unlucky animals drift into their path, but to the animals they hunt, jellyfish are a menace. Their venom often kill creatures hundreds of times their size, including, in rare cases, humans.

As scientists study jellyfish more closely, a new creature is emerging: More than just a nuisance, jellyfish are viewed as barometers of ocean health and possibly a powerful force affecting seawater itself.

Unlike sharks, jellyfish thrive in ecosystems damaged by human activity. Oceanographers have found a common symptom among places where overfishing, chemical pollution and rising sea temperatures have killed off other species: more jellyfish.

Read (Global Post)