In our area they reseeded mangroves on flats areas. To keep currents, tides, boat wakes, etc. from washing them away, this method was used. A piece of PVC pipe was knocked into the substrate so the top of the pipe was just above the water line, and the mangrove seed was dropped in. When the seed rooted and was secure to the bottom, the pipe was removed. I read about it in our local newspaper and they reported very good success with this method.