Creature Feature: Sea Butterflies

With a name like sea butterflies, they have to be great!

Pteropod or “sea butterfly,” a tiny sea snail that drifts in the ocean, catches marine “snow” and provides food to the whole ocean food web. Image from a video clip from research conducted by Nina Bednarsek and Richard Feely.

Underwater Flyers

Sea butterflies aren’t related to butterflies, but they do fly and they also begin life in a different shape (larva) than they end it. They are actually tiny, marine snails that live their whole lives as plankton, drifting through the ocean in an endless, floating flight.

Sea butterflies are also known as pteropods (look up “ptera” and “pod” to see what they mean in Latin. Is this a good name for sea butterflies?) Unlike their snail cousins, their feet are made for flight, not creeping along on the sea floor. Some pteropods have shells, like most snails, and some species have ditched their shells to fly free. These naked pteropods are also beautiful and some people call them “sea angels.”

Snot, Sea Snow and Superstar Recyclers

Shelled pteropods have a pretty peculiar way of snagging their next meal. They make a net out of mucous (yep, snot) that they cast out around them and let it catch marine “snow.” Marine snow is made of dead stuff, poop, and parts from marine plants and animals that sinks slowly to the ocean floor. Most of it looks whitish and can gather colonies of bacteria on its way down. Sound good? This is nutritious stuff! Pteropods make a good and seemingly lazy living out of snow-catching. All this is going on with a creature the size of the head of a pin. Pteropods without shells work a little harder for their meals, which may consist of mainly shelled pteropods.

Pteropods fill about 10-15% of young Pacific salmon’s bellies at snack time in the sea. For folks, fish, and resident killer whales who depend on the salmon, that’s one meal we don’t want our favorite fish to miss! Salmon aren’t the only one who eat pteropods, fish from flounders to sharks do, too, and even other drifters, like jellyfish catch them when they can (which isn’t hard, they’re not in a hurry).

Acid and Shells Don’t Mix

A pteropod shell with cracks forming from exposure to water that was too acidic to keep their shells intact.

These delicate sea butterflies have transparent shells. You can even see their hearts beating right through. How cool is that? The shells are made of the same stuff that clam and oyster shells are made of: calcium carbonate. What’s even cooler is that snails and other molluscs make their shells out of ingredients that are dissolved in sea water, calcium and carbonate. A chemical reaction in the mollusc’s mantel (the layer of tissue between the shell and body) turns these two ingredients into shell….unless the water gets more acidic.

When that happens, the shell-making reaction goes in reverse and shell gets thin, cracks, breaks, and eventually disappears.

How does water get more acidic?

No one is dumping acid into the ocean on purpose. But its acidity is rising. This happens when carbon that’s in the air (carbon dioxide) mixes into the seawater. Yep, what’s in the air is also in the water. When there is a lot of carbon in the air, it turns to a weak acid when it mixes with water. There is always carbon in the air. It’s what we animals breathe (or toot!) out, what living things give off when they die, and what goes up with the smoke when stuff burns.

Pteropods in normal sea water on the left and in more acidic seawater on the right. Images by super-cool oceanographers, Nina Bednarsek and Richard Feely.

Burnin’

We burn lots of stuff, especially coal, gasoline, and oil (fossil fuels). We’ve burned so much that the ocean is turning the carbon from the air into acid. That doesn’t mean the ocean is acidic, but its acidity is increasing a lot from what it used to be before we started burning so much fossil fuel. Scientists call this ocean acidification. Scientists like super-cool oceanographers, Nina Bednarsek, who received the SeaDoc Society Salish Sea Science Award for her brilliant discoveries about how ocean acidification changed pteropod shells and just how acidic water has to be to start damaging their shells. She is definitely a Salish Sea Hero! And also scientists like the 4th graders in Mr. Del Prete’s class at Crescent Harbor Elementary. They even published their own book about ocean acidification because they researched a lot about it and want the world to know it’s time to slow it down. That’s the kind of thing Salish Sea Heroes do.

Do we have to burn so much stuff that our ocean gets acidic? No. Can we fix it? Yes we can! (credit: Bob the Builder). How? The Crescent Harbor 4th graders say we can ride bikes, walk, and ride public transportation instead of drive. We can turn off lights and unplug electronics in our homes when not in use. We can buy stuff without so much plastic packaging. And we can help restore ecosystems that store carbon and keep it out of the water, like wetlands, salt marshes, eelgrass meadows, and especially mangroves. You can even plant a tree or shrub in your own yard or balcony. That helps, too.

What we do to decrease burning stuff will go a long way to rescue tiny pteropods, their shelled relatives, and all the ocean life that needs them to survive.