Last week we looked at sea angels, an aqua-slug whose "foot" has split into wings. And what do sea angels eat? A type of winged sea snail known as a sea butterfly. But sea butterflies are feeling the chemical change as the oceans are becoming more acidic, putting their entire aquatic ecosystem at risk.
Sea butterflies are sea snails that decided to leave the ground behind. Over time, their feet morphed into "wings," and they use them to waft themselves through the ocean. Researchers have known about sea butterflies for some time. They live all over the world and there are plenty of old sketches of them (all of which look like rejected sketches for monsters in the Alien films). They turn up in nets, and in the fossil record.
They're not more commonly known for two reasons. First of all, they're small. Most of them are only a centimeter long, with tiny, almost translucent shells. (Many have lost the shells, and so weren't always classified with their brethren.) Secondly, they spend their days well below the surface of the ocean (25 meters), migrating to the top only at night.
People are taking more notice of the butterflies now for an extremely sad reason. Their shells are delicate, both chemically and structurally. The calcium carbonate dissolves in acid, and without that protective shell, sea butterflies usually perish. Because they are at the bottom of the food chain, their loss ripples up and impacts higher-order creatures — including sea angels.
Even the types of sea butterflies that don't have shells tend to prey on things that do have shells. So scientists are watching these creatures closely to see if they're the first domino in a line that ends in a major ecological collapse.