This is my general idea for artificial floating coral reefs, like the topic title says.
The basic reef unit would be a column, with a float (I’m thinking a 55 gallon drum or some other big floating device) and a weight at the bottom, to keep the column upright. Between the frames would be a trellis structure, with different beams and sections of fencing and such to create different surfaces with different spacing. Corals could by propagated onto this and allowed to spread naturally, or position the empty columns adventurously during the annual coral spawning to get as much new growth as possible. These columns could be used to create a floating reef around the main seastead, and would be unaffected by rising sea levels, since they float (they would, unfortunately, be vulnerable to other effects of climate change such as ocean acidification, changing temperatures, and changing salinity due to the melting of glaciers). They could be used to create artificial reef in any depth of water, they would just need to be connected to each other and the seastead, perhaps by more underwater connecting trellises. This would also allow us, pending on how we attach them, to create new reefs, change the structure of our old one (to create new harbor channels, for example), or to build connecting reefs to nearby seasteads. Perhaps on the seastead itself, the buildup of solid rock would protect the hull against some of the natural elements, increasing the lifespan of the seastead.
This would drastically increase the productivity of the region, since open ocean could suddenly support much more life, and the seastead would also benefit from tourism. Imagine snorkeling in clear water looking at coral reefs, with a blue fade-out background beneath. I think it’d be pretty cool at least. Also, they could help buffer the seastead from storms and provide natural protection against raids on all sides except where the harbor channel(s) would be.
I would also think the design could be used to support other varieties of marine life. Pending on the location of the seastead, the bottom barrels could be used for kelp, and the hold-fasts would safe from sea urchin attack. Perhaps other sea grasses could be planted in some specially designed one, which would also increase the variety of life and productivity of the region. Kelp as a plant has many practical uses for humans as well. Perhaps we could get our own paper through harvesting kelp, since it can grow pretty fast.
I am also considering testing if a similar design could host mangroves (I don’t know if they get their nutrients from the mud or not, since it is fairly anoxic among other things. I read somewhere that they get a lot from the roots above water or something. This is why I will test.). These would help a seastead immensely, since we could get wood (for whatever mangrove wood is actually good for…), as well as perhaps making a solid ring of floating mangrove forest around the seastead, to act as a natural storm break, similar to their role on land. Picture it like a target, with the seastead as the bulls eye, the coral reef as the next concentric ring, and the mangroves around that. Lots of protection and lots of habitat.