High-Altitude Life?

Question

So here’s the rough idea. I’m trying to figure out what kind of life could exist that spends basically its entire life in the air, for an alien world I’m working on. No sentient life, just wilderness. In my mind, it’s not so much something that actively flies (like birds or planes), and lands in-between, but something that literally never stops flying. It is born, eats, breeds, lives, and eventually dies in the air. So my main questions are these:

• What would be necessary for there to be an actually functioning aerial ecosystem, and how complex would it be? Would it be similar to a ground ecosystem, or would it have to be completely different?
• What kind of life would it be? Plant, animal, fungi, single-celled, or maybe something else entirely? What is/would be best suited to life in the air?
• How would it fly? Would it be some sort of living gasbag, or something kind of like spiders ballooning, but on a much larger scale? Maybe something like a living glider? Or jellyfish-type propulsion? Is using magnets to float around in the geomagnetic field at all possible?
• How big would it be? Would it be one big organism, or a giant colony composed of millions of tiny ones?
• What would it eat? Would it have to go down near the ground to feed, catching low-flying/ground life, or would it catch other aerial life in midair? Could it maybe strain smaller forms of life out of the sky, like whales eating krill?
• How would it reproduce? Would it have a larval/seed stage on the ground, where it releases seeds/spores/polyps/eggs/larvae/whatever that fell to the ground, grew, then took off?
• How high would it be? It is confined to a certain altitude, or can it move around? Could there be life all the way up at the edge of space?
• What would be different about the planet itself that could help this happen? Would the atmosphere be composed of some heavier gas that could make it easier for other gasses to float? What about the planet itself having less gravity?
• What happens when the life dies? Does it go crashing down to earth, or just float around and decay, forming a place for new life to grow?

I think that’s pretty much it. I’m also interested in what possible mechanisms would be needed for life like this. Also, if there’s anything that just makes this whole thing blatantly impossible, then tell me so that I can hopefully handwave around it.

Answer 1

The Gibble

I created a species of flying creatures a few years ago. They're like a mixture of Blimps and manta rays. They are shaped like manta rays, and have an air sack they fill with gases like helium using special gill like filters. They use the appendages by their mouths to catch other flying prey (perhaps HDE's little pufferpolyp friends).

These creatures also fly in swarms, with the females in the middle. The babies grow on the mother's belly in a special clear sack. This means the females have larger air sacks; so they can carry their babies. The babies learn how the males protect the females, see their parents catch food, etc. Once they are fully developed and ready to fly, they either puncture the sack, or spit acid on it to dissolve it. I haven't decided which. Life goes on (for everyone but the pufferpolyps).

These creatures would have a lifespan of about twenty years, and they periodically refill their air sacks. Their filters can control the amount and type of gas in these sacks, to adjust the elevation the creature sides at. If they died of disease or old age in the air, their sacks would slowly leak and they'd drift to the ground. Or they'd be eaten by some other creature first.

While these creatures may look like manta rays, they are very different on the inside. Their bones would be hollow, their "wings" would catch up drafts, and their wingspan be more along the lines of three feet, instead of three yards. (Scaled down from actual manta rays.)

Answer 2

Musca Turbela

A type of fly that has evolved to swarm in large airborne "mats." A swarm starts when a number of flies find a piece of airborne matter. They latch themselves to the underside and keep it afloat through sheer numbers, feeding off of it, breeding, laying eggs, dying, pushing their waste and the newly-dead into the "anchoring mass," hatching, and continuing their quick life cycle. Eventually, the mass (and supporting swarm) is large enough to collect rainwater and support algae (and eventually some other flora). Mature mats would look like an airborne set of black-grey stalactites slowly and loudly hovering maybe 50-150 meters off the ground, surrounded by a cloud of loose flies and capped with some greenery (moss, tendriled plants that primarily catch moisture out of the air, various carnivorous plants). Birds would be attracted to these mats by the plentiful food, but carnivorous plants would be evolutionarily motivated to trap birds and provide food for themselves and the flies they primarily subsist on.

The planet in question would either have to have a rather hostile surface to drive these insects to make permanent residence in the skies, or have significantly lower gravity than earth to make this type of arrangement a convenient way to avoid ground-based predators.

Answer 3

The Hindenburg Fish. Pinnacle of aero-piscine evolution!

Fish have swim bladders that are currently filled with air in order to control buoyancy. The Hindenburg fish (through an unfortunate accident including a bottle of tequila and an electric eel) gained the ability to decompose seawater into oxygen (that it uses to supplement it's O2 requirements) and hydrogen (which fills the swim bladder). Now shoals of Hindenburg fish can be seen swimming along the coastlines of many countries, though they never venture too far from water sources in case they need more gas. Their eggs can be found laid in rock pools and shallow waters everywhere.

Their volatile nature has led to a whole new dining experience, known as 'Oh, The Fuganity!', where skilled chefs attempt to slice sashimi from the Hindenburg Fish without causing it to accidentally detonate in their diner's faces.