Could Mangroves be used in mitigating sea level rises?

Hi there!
This waffle is about a topic that I recently overheard at a couple of different meetings
(an environmentalist group, a freethinking/communication skills club, and a skeptical thinking club)
and I wanted to further investigate/deconstruct the elements in the claim... mainly so I can understand what they're meaning more and engage at the next meeting.

So,
some people were converging on sea level rise: they were arriving at that conclusion from a number of different perspectives (climate skeptics were playing devils advocate, to try and understand the hypothetical and get into some numbers).
Some people brought up Seawater Greenhouse, desalination and mangroves of all things...
as potential offsets for sealevel rise etc.

In the past, I've heard some spurious claims about mangroves, from use as a natural pump in elevating water (along with Oak Trees and Cacti, etc) which can be plausible depending on the claim made,
through to a 'natural liquid-separating device', which separates liquids according to viscosity (so, you could get salt water to separate into wine, for example...) - this can get quite technical with discussions of capillary functions etc

Proponents of mangroves essentially argue that
"if you must plant trees, then why not plant the 'triple threat' tree of mangroves, since mangroves will ward off sea level rise, will also act as desalination sources (to increase availability of drinking water), and will act as natural carbon sinks, if indeed carbon is behind warming phenomena". an interesting claim...

So, lets waffle a little about this;
I'm approaching from an ERoEI perspective: how many mangroves would we be needing to plant and raise here... for there to be any effects approaching that which the proponents describe? Is this feasible when compared with other processes?...
Mangroves are admittedly pretty awesome plants, they look cool, and do some awesome stuff.
But you'd need a lot of them to be planted along coastlines for a long time, and they'd have to survive... and you'd then have the classic 'unforeseen sideffects' because Mangroves are not native species in all landmasses.
Mangroves also require certain environmental conditions to thrive and survive... and this is where the technocrats/Meliorists show their true colours.

"But we could genetically modify the mangroves..."
here we go.  Genetic engineering to the rescue!
It's fun, and I find it a worthwhile aside to ask at this juncture a couple of questions;
does that individual like to drink recycled water when given the choice between 'natural water' and recycled water?
does that individual like to eat GMO food sources, from a human security perspective (knowing that our food sources are becoming less biodiverse and more vulnerable to 'contagion')?

Okay, digression aside,
lets assume we could modify the mangroves, to both optimise those mitigating effects, its survival chances in a wider range of climates, reproductive clumping rate etc... (so this plant would potentially be part artificial plant/biological fluid separator and catalytic converter?, part sunflower, part cacti, part bamboo/weed and part mangrove?)

That still won't allow you to plant anywhere near enough mangroves in the coastline areas in which they are required, to achieve the desired effects. Bare in mind this discussion has until this juncture, eschewed the ERoEI/Fossil Fuels required to both produce the mangroves (which goes up if we need to GMO the mangrove) to then go and plant... the planting energy costs would also be quite high...
what sorts of fertilizer quantities and nutrients would be needed to sustain all these mangroves? 

When you compare this with other methods and approaches to
'combating climate change'/mitigating some of the potential impacts of climate change...
such as doing nothing/adapting to the rate of change,
reducing the number of people (who generate demand on climate/experience the climate change) via a plethora of ways;
using seawater greenhouse technologies, or technologies along with desalination,
redirecting the water (either underground, to some other geographical region ala Panama Canal style project) or even
literally blowing up the water...
other methods are much more ERoEI efficient and/or have fewer sideeffects.
 I find it all to be a fascinating discussion, because then you get the next order of discussions - combinatorics! You then get people who say that perhaps a combination/configuration from the set of these partial solutions will emerge the set of 'optimal solution'...

This becomes entertaining;
so what ratio of 'genetically engineered mangrove planting' to 'cloud seeding' to 'reduction rate in people' to 'desalination plants/seawater greenhouses', to "diverting the water" to 'literally blowing up the water' do people envisage as this 'optimal solution'?
"I feel 15% of the optimal solution is apportioned to 'literally blowing up the water'"... and so on.

So,
what do you think?
I'm keen to hear from a wide range of people on this subject, what's your take on it?
Could mangroves be used to mitigate climate change? If so, how do you arrive at that conclusion (as it would be fascinating to see the ERoEI justification for those technologies).