Piggybacking on the previous “Reef World” questions.

Let’s talk Flora and how it adds to life and the environment on Reef World.

The entire planet is mostly covered in shallow ocean, but not completely. There are some depths, but the tectonic activity is pretty much done. There is one last massive Olympus Mons type volcano spewing out the planets remaining inner heat, and the core has slowed down and become a large nickel iron ferro-magnet.

Free roaming islands of Pumice float around closer to the volcano, but they don’t last long. Even though unknown substances within the pumice islands (we’ve taken to calling it Wavnium) keep them afloat longer they still crumble apart after enduring months of rough seas. But during their time the Wavnium makes them quite large before they fall apart. This gives them the “ability to absorb [and distribute] many potentially advantageous elements/compounds. For at least these reasons, astrobiologists have hypothetically proposed pumice rafts as an ideal substrate for the origin of life” (https://en.wikipedia.org/wiki/Pumice_raft).

The reef throughout the planet benefit from this. These alien version of Coral create Reef that are more robust than Earth counterparts. “Sea grasses live in between the coral reefs, and they transfer nutrients to the coral. Their roots are adapted to keep the plant in place during strong ocean currents. When the sea grass dies it helps to create future plant growth. Mangroves grow [on and up from] the Coral Reefs. They grow above the sea water, and their roots protect from the sediment overpowering the coral (https://coralreefbrawner.weebly.com/plant--animal-adaptations.html).

There are areas of Sargasso, and Kelp forests as well, in competition with the Reef and Mangroves.

"A continual drizzle of dust falling from planetary rings seeds the oceans with ample nutrients." We theorize there may have been a small moon in a very low orbit that crumbled apart just below the Roche limit some time ago (potential source of Wavnium?).

The air on reef world is breathable because there are cyanobacteria and multicellular organisms like the Coral, and fish equivalents. These Mangrove forests are also part of producing air.

p.s. The gravity of the planet is lower than Earth but greater than Mars, and well within the escape velocity to retain an atmosphere and oceans.

Is this flora set up possible, and beneficial to habitability, both human and/or native?

  • $\begingroup$ The question kind of presupposes that the conditions are good for life, so what exactly is the question? Humans aren't well-adapted for a "Waterworld" existence, but I'm sure they would manage, and there are monkeys that live in Mangrove forests and rarely touch land. What are your natives like? Merpeople? Intelligent Sea Otters? $\endgroup$
    – DWKraus
    Commented May 12, 2021 at 21:24
  • $\begingroup$ You should narrow this down a bit, for one thing native life will adapt to whatever the local conditions are so no need to ask about that. Plausibility is covered in the questions leading up to this, so really you should just be asking about the impact on humans, for that we will need to know what the humans are doing on the planet are they colonizing or just exploring. $\endgroup$
    – John
    Commented May 13, 2021 at 14:21
  • $\begingroup$ @John, Lets go with the humans are just exploring for now. $\endgroup$
    – Len
    Commented May 13, 2021 at 17:32
  • $\begingroup$ @DWKraus, (repost) that would be the next question. human explorers would live on whatever they came in, on rafts or atolls they build, maybe in the mangrove forests, maybe even the pumice islands temporarily. As for natives As for natives I was going to try for a creature that can breathe water in and out the same way crabs do(?) $\endgroup$
    – Len
    Commented May 13, 2021 at 17:37

2 Answers 2


A few Thoughts:

Your question is a little open-ended, so I'm going to give an open-ended answer. Hopefully it gets to the spirit of what you're looking for.

Just a thought. You like the pumice island idea, so maybe a native plant-organism has evolved to deposit a waxy coating on the pumice, intercalating pumice islands into a sort-of matrix of wood and pumice lumps. It would form the basis of a much longer-term floating island. Possibly sink 'anchors' (modified roots) to keep the islands from floating away, and then using the roots to mine the seabed for nutrients and help overcome the need for constant sediment washing. Willk is right that there would be strong winds. When the islands run out of nutrients, they 'raise anchor' and float elsewhere.

You might also get around the nutrient problem in the same way a forest does, with a fungus-like organism that digests the rock and sediment, and then has a symbiotic relationship with a carbohydrate source like an island-tree or floating plant. The abundance of sediment and great depth of ocean make evolving such a relationship trickier on Earth, but the abundant shallow ocean and lack of sediment make nutrient recycling by a pseudo-protist a much more favorable solution. This also accounts for the degradation of land and atolls. They're like carboniferous wood - digested to free up the nutrients once the appropriate organism evolves.

Another solution to the nutrient problem might be a Venus fish-trap. The Venus fly trap isn't digesting flies, it's trapping them to rot, so it can use their minerals. Symbiotic protist-like organism could work with a plant, the plant trapping fish in a net/trap, with the protist digesting the fish, feeding the nutrients back to the plant. The combined symbiotic collective would work like a sponge, or (if free-floating) like a filter-feeding whale.

Finally, although it might violate the reef-world theme slightly, why NOT trees anchored on the bottom of the ocean? Rising up like oil derricks, trees could extend out of the water for the same reason trees do on Earth: To outcompete the other plants for sunlight. a floating, anchored plant or deep-water mangrove could, over time, establish a weight-bearing stem and rise up out of the water higher and higher. Such forests would resemble swamp environments, and provide vital ecosystems in the same way mangrove swamps do on Earth. With high winds, strong stems would be needed to resist, and the deep stems & roots would liberate sediments.

  • $\begingroup$ thanks for the alternatives. I'll consider them. I'm curious about the high winds though. What does that do to a shallow ocean in lower than Earth gravity? $\endgroup$
    – Len
    Commented May 13, 2021 at 8:08
  • $\begingroup$ @Len I'm not a meteorologist, I'm afraid, so It's more of a hunch there would be winds, plus Willk saying there would be. I'd see how winds develop over oceans, though. $\endgroup$
    – DWKraus
    Commented May 13, 2021 at 10:07

Riff on coral!

Sediments will not be as big a deal with no land to wash them out of. I think it would be tough for the poor mangroves. There are going to be serious, serious winds in this world with nothing but mangroves above the water.

I think your photosynthesizers should be animals with endosymbionts: coral, sponges and jellyfish. Instead of trees you can have jellyfish that hoist themselves up on high places and put out photosynthetic fronds. If winds tumble them into the water, no harm donw.

  • $\begingroup$ So it's a windy planet? Because no mountains and such? What does that do to a shallow ocean in lower than Earth gravity? $\endgroup$
    – Len
    Commented May 13, 2021 at 8:05

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