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.