First time that I'm seeing this thread, and As a partial homegrown botanist myself, not a professional by any means here!!!!, but Ive had many years of clipping and grafting trees, shrubs, vegetables and (other) green plants(part time at a green house), so I'll chime in and say Mangroves WILL and CAN be cloned, it is pretty easy for them to root if done properly, I helped a buddy clone his about a year ago, 6 were cloned and 5 survived

, fresh water IS needed and a MUST!!, also a root hormone is needed( gel/power) gel works better from experience , 24hrs lights for at least a week or two before cloning, once you have cloned it, put it in a fresh water bath for at least 1-2hrs, this will help take out the salt in the fresh cut stem also help the clipping to start absorbing the fresh water, place a power head and heater in a tote or small tank basically anything that will hold water and be able to put a clear lid on, basically your making a hydroponics green house.
INSTRUCTIONS:
-24hr light 1/-2 weeks
-clip cutting on a 45degree angle with a least 2-3 sets of full leaves
-1-2hr fresh water soak giving the cut end a few light sqeezes while in the fresh water just before removing
- place 2 slices virtically along the original 45degree cut
-place cut end in root hormone for 1-2 min
- put cutting in a rock wool cube
-Place cube in tank/tote
-put enough water in tank to fill just 1/4-1/5 the cube you will probably need to suspend the cubes in the water coloumn to have enough room for power head and heater
-place lid on
-24hr light for clones
-t5 lights work best( 2bulb) 2-3" above lid
-remove lid every day or two for fresh air
- monitor water and temp. Levels constantly 78-80degrees 1/4-1/5 up the cube
- humidity around 80-90percent
-replace water every 2 weeks(max) with fresh RO
-within 5-8 weeks you should start to see a root ball forming at the cut, if not before that in two weeks it will start to rot away, at 10-12 weeks roots should start to come out of the cube, at that time the cube will have started breaking down, pull apart gently, plant as needed

, I'll see if he has any pics of what we did, if any other questions hit me up

For a first time ever cloning a salt water plant and having read up on it first id say 5 out of 6 is a successful cloning
Thx Sean