Corals usually need a hard substrate such as rocks to attach themselves on and to grow on.
The soft muddy-like ocean floor is not a great anchor for coral polyps.

This why corals often grow on large sunken metal ships. (Wooden ships decay).
But besides sunken ships there is another method to help corals grow. Called Reef Balls.

Reef Balls

Reef balls are hollow semi-spherical to conical structures of pH neutral concrete, which do not degrade in seawater and are safe for marine life. The reef balls have holes inside for fish and currents to go through.
And the surface of the concrete is rough so that it is easier for microbes and corals to attach to.

Studies have shown that reef balls seems prospective for attracting corals and the fish and marine life communities that come with them.
On top of that reef balls used in front of shores are able to function as breakwaters to reduce strong currents and stabilize shores from erosion, just like natural reefs.

Cremation

Another interesting thing about reef balls is that the cremated ashes of the deceased can be mixed in with the concrete.
In this way you can “bury” your loved ones at sea and make them permanantly become one with coral reefs. How great is that?
Many “memorial reefs” made out of reef balls have already been created. And the option to mix one’s ashes with a reef ball inspires more people to add more reef balls to the ocean, which whill help to grow more coral reefs.

Seed balls

When I first heard about reef balls I immeadatly thought about Fukuoka type seed balls and I am happy to see that this kind of technology can also be applied to support the development of marine ecosystems. I do not know if reef balls were ever inspired by seed balls,
but they function in a similar way. Both seed balls and reef balls can profide the subtrate and building blocks for life to spawn, especially in barren areas.
The biggest difference is that reef balls are several thousands of kilograms heavy and require cranes to be deployed in the ocean.
While seed balls are small clay balls the size of a nail and can be thrown around by hand.
Another difference is that seed balls already contain seeds inside the clay ball which sprout once a rain comes.
Reef balls on the other hand are just concrete structures with no initial life inside, however often divers will transplant corals and other marine life onto the reef ball after it has been deployed.

Smaller reef balls are also being used to plant mangrove trees for mangrove restoration.

More about reef balls

If you want to know more about reef balls you can visit the following websites below:

https://reefballfoundation.org/about-reef-ball/
https://reefinnovations.com/reef-innovations-restoring-marine-ecosystems-with-reef-balls/
https://www.eternalreefs.com/