Last year, sea urchins in the Caribbean Sea started getting sick. Their spines fell off. Their suction-y feet lost grip. Eventually, the urchins died. Who or what was the killer?

Scientists think they know.

God made all creatures with a purpose. The urchin keeps coral clean. Urchins are great grazers. They move slowly along the sea floor, gobbling up algae.

Where would the world be without urchins? Sea stars, cod, otters, and lobsters would miss their urchin dinners. Even worse, algae-coated coral reefs couldn’t get the sunlight they need to live.

No coral reefs? Thousands of species of sea animals would lose their homes.

A lot depends on these sea lawnmowers!

Black, long-spined sea urchins started getting sick in droves in 2022. They were dying all the way from the Virgin Islands to Puerto Rico to Florida. Ocean scientists recalled a bad die-off in the 1980s. It slashed sea urchin populations by around 98 percent. That cause was never known.

This time, an international team of researchers looked for clues. They took samples from sick urchins and healthy ones. What did they find?

Viruses? Nope.

Bacteria? Nope.

But they did spot traces of tiny, single-celled organisms called ciliates (SILL-ee-ates). The ciliates showed up only in sick urchins.

Most ciliates don’t cause disease. But this kind has been linked with other water outbreaks. Prime suspect!

To confirm they’d caught the killer, scientists placed the parasites in tanks with healthy urchins. How would the urchins react? Out of every 10 urchins, six died . . . after first losing their spines and suction.

“The case is closed,” says Mya Breitbart, a marine microbiologist at the University of South Florida.

Next step: Find out how to stop the ciliates.

Why? Even the most unnoticed creatures play a big role in keeping creation in a healthy balance.