What they are
Around 70 tree and shrub species. Unrelated families. Same trick: surviving salt water and anaerobic mud.
You find them between 25 degrees north and 25 degrees south. Southeast Asia holds the deepest diversity. Everywhere else, you get a handful of species doing the heavy lifting.
The roots tell you who's who. Red mangroves (Rhizophora) drop arching prop roots from the trunk. Black mangroves (Avicennia) push pneumatophores up through the mud like pencils. Both are breathing tubes. Tidal mud has no oxygen, so the trees breathe through the air.
How they handle salt
Three strategies, depending on species.
Excluders. Rhizophora filters salt at the root membrane. Most never enters the plant.
Excretors. Avicennia drinks the seawater and dumps salt through leaf glands. Run a finger over the underside of a leaf and you can feel the crystals.
Accumulators. Some species shunt salt into old leaves and shed them. Slow but effective.
This is why mangroves own the intertidal zone. Nothing else can pay the salt tax.
Why they matter
The math is brutal in their favor. Mangroves cover 150,000 square kilometers, under one percent of tropical forest area. They deliver coastal protection, fisheries, and carbon storage worth 33,000 to 57,000 USD per hectare per year.
A kilometer of intact mangrove cuts storm surge height by 60 to 80 percent. Villages behind cleared coastline die in cyclones. Villages behind mangroves don't.
Blue carbon. Waterlogged soil stops decomposition. Organic matter piles up as peat for centuries. One hectare can hold 1,000 tonnes of carbon in soil alone, three to five times what a native oak forest stores. Clear the mangrove and that carbon oxidizes within years.
Nurseries. Roughly 75 percent of commercial tropical fish species use mangroves at some life stage. Snapper, grouper, shrimp, mud crab. Cut the mangroves and the reef fisheries collapse a decade later.
What's killing them
Between 1980 and 2000 the world lost a quarter of its mangrove cover. The driver was shrimp aquaculture, then coastal real estate, then rice paddies. Myanmar, Indonesia, the Philippines: 30 to 50 percent gone.
The cruel part. Shrimp ponds built on cleared mangrove fail within 5 to 10 years. Soil acidifies. Disease takes the stock. You're left with a salt pan that grows nothing.
Sea level rise adds pressure. Mangroves migrate landward when they can. Most can't, because the land behind them is now a resort or a seawall. Pollution finishes the job. Mangrove mud traps everything: oil, plastic, heavy metals, fertilizer runoff.
Restoring them
Most early projects failed. People planted Rhizophora propagules on open mudflats with no protection, and the tide washed them out within a month.
The fix is hydrology first. Robin Lewis called it Ecological Mangrove Restoration. Repair tidal flow before you plant anything. Breach abandoned shrimp pond berms. Let the water do its work. Mangroves recolonize naturally if the hydrology is right and a seed source is nearby. Plant only to fill gaps.
The Casamance delta in Senegal got 150 million trees back since 2008 through community-led work. Pakistan's Indus delta planted 100 million seedlings across 100,000 hectares. Indonesia is converting failed shrimp ponds in Java back to forest. Bakhawan Eco-Park in Aklan, Philippines, runs as a community-managed model with tourism revenue.
The work is technically solved. The politics are not. Land tenure, cheap shrimp markets, and coastal speculation drive the loss faster than any project can replant.
Field rules
Never plant on a bare mudflat without checking elevation and tide range first. Sit and watch one full tidal cycle. Mark the high water line with stakes. Plant above mean sea level, below mean high water. Outside that band, mortality runs above 80 percent.
Match the species to the zone. Rhizophora at the seaward edge where wave energy is highest. Avicennia mid-zone, where the mud is softer and oxygen lower. Sonneratia and Nypa further inland, into the brackish reach.
Use local seed. A Rhizophora propagule from 500 km away may not match the local salinity regime, and you will see it sulk for a year before dying. Collect from healthy parent trees within 20 km of the site.
Protect for three years minimum. Goats eat the tips. Fishers cut straight poles for traps. A single oil spill or a buried tire dragged in on a storm tide will undo a hectare of work in one night. Budget for a fence, a paid watchman, and signage in the local language.
When it fails
Three failure modes show up again and again.
Wrong elevation. Propagules planted too low drown. Planted too high they desiccate at spring tides. The cure is a tide gauge and patience.
No seed source. Even with perfect hydrology, mangroves need parent trees within drift range. If the nearest forest is 10 km away, you have to plant.
Unresolved upstream pressure. If aquaculture effluent still flows into the site, no amount of planting holds. Address the source first.