The mangrove and bolongs of Casamance: a vital ecosystem and the challenge of preserving it
A true green lung of southern Senegal, the Casamance mangrove is an essential amphibious ecosystem. Lining the maze of bolongs — those tidal arms of the sea — and made up mainly of mangrove trees (Rhizophora and Avicennia), it acts as a buffer against coastal erosion, forms a vital nursery for marine life and represents a major carbon sink. Despite a recent regeneration trend, this ecosystem remains extremely vulnerable, facing growing pressures that are both climatic and human. This feature takes stock of it, from its biodiversity to the threats it faces, through to the restoration techniques that are restoring hope.
Mangrove species and the zoning of the estuary
The Casamance mangrove is made up mainly of three mangrove species, each occupying a specific zone of the estuary — the zonation — according to salinity and how long it stays submerged.
Rhizophora mangle, the red mangrove
A pioneer species and the most emblematic of all, recognisable by its spectacular stilt roots plunging into the mud. It grows on the front line, in daily contact with the water.
Rhizophora racemosa
Very close to the previous species, it tolerates slightly less salty water and grows further upstream in the estuaries, sometimes reaching impressive sizes.
Avicennia germinans, the black mangrove
Set further back, in the higher and saltier areas (close to the tannes), it has no stilt roots but a network of pneumatophores: vertical roots that point out of the mud like tubes to draw oxygen from the air at low tide.
Together, these mangroves trap sediment, filter brackish water, hold the coastline in place and store carbon on a massive scale — one of the most efficient « blue carbon » sinks on the planet. Above all, their tangle of roots offers an irreplaceable nursery for juvenile fish, shrimp and oysters.
The main threats
The degradation of the Casamance mangrove began with the great drought cycles of the 1970s and 1980s, but today's threats are mostly linked to human activity.
Hyper-salinisation and climate
The historic decline in rainfall, combined with strong evaporation, has caused extreme salinisation of the Casamance river waters and acidification of the soils. The result is the formation of tannes, those vast bare, over-salted expanses where vegetation dies.
Overexploitation of wood
Mangrove wood is hard, dense and termite-resistant. For a long time it was cut on a massive scale as firewood — notably for smoking fish — and as construction timber; traditionally it was also used for the ceilings of Jola houses, particularly impluvium houses. Carried out by directly mutilating roots and branches, and above all driven by charcoal production, this cutting has ravaged entire stretches of mangrove. That is why cutting mangrove trees — like the traditional use of their wood for frames and ceilings — is now formally banned, even though illegal cutting persists.
Destructive oyster-harvesting practices
Traditional oyster harvesting, since the oysters cling to the stilt roots of the mangroves, still too often ends with the roots simply being cut off, which weakens or kills the tree.
Urban sprawl and infrastructure
Demographic pressure around towns such as Ziguinchor is eating into peri-urban mangrove areas. At the same time, poorly designed infrastructure — certain bridges or anti-salt dams — has altered the natural hydrodynamics of the estuary, encouraging silting and blocking the regulating flow of the tides.
Ecological and socio-economic consequences
The loss of mangrove cover triggers a chain reaction that directly affects local communities, particularly the Jola, whose culture and economy are intimately bound up with it.
| Impact | Concrete consequences on the ground |
|---|---|
| Collapse of fish stocks | As the mangrove serves as a spawning ground, its destruction makes fish, shrimp and oysters scarcer. This hits hard the income of women, who handle processing and selling — a role we set out in our feature on fishing in Casamance. |
| A threat to rice growing | The erosion of the natural mangrove barrier lets salt water seep inland. The traditional rice paddies, laid out behind the mangrove, are eaten away by salt and then abandoned. |
| Worsening coastal erosion | On the Atlantic coast and in the estuary islands (Carabane, Diembéring), the sea is advancing alarmingly. No longer slowed by the forest, the waves tear away the banks and directly threaten homes. |
Regeneration and sustainable management
Since the early 2000s, there has been a genuine awakening. Thanks to large-scale replanting campaigns led by local communities and NGOs such as Océanium de Dakar, the trend has reversed locally: satellite images now show a slight overall increase in mangrove cover in areas such as Oussouye and Énampore.
But replanting is not enough unless it is coupled with sustainable management. Top-down projects sometimes meet a lack of social acceptance. The challenge now is to give economic value to standing mangrove — through ecotourism or REDD+ carbon finance — and to train local people in non-destructive oyster harvesting methods, such as collector garlands.
Community replanting techniques
The success of restoration campaigns rests on a fine understanding of local flora and on forestry techniques adapted to the rhythm of the tides. The most widespread and effective method is direct sowing of Rhizophora propagules. Propagules are the tree's dispersal organs, shaped like long green candles; already germinated while still on the tree, they are harvested when ripe by villagers, often organised into watch committees.
During the rainy season (the hivernage), volunteers wade into the mud at low tide to plant these propagules vertically, two thirds deep, in the soft sediment. The success rate is high, as the plant roots very quickly before the following tides can dislodge it. For Avicennia, whose seeds are small and flat like beans, the preferred approach is protective enclosure — shielding degraded areas so nature can do the work — together with restoring freshwater circulation to wash excess salt out of the soil.
Exploring the bolongs by pirogue, safely
These challenges are part of the wider picture of ecological protection in Casamance. Understanding the mangrove cannot be improvised: navigating the bolongs demands a fine knowledge of the tides and the channels. That is why we have documented several Casamance discovery itineraries, designed as respectful ecological immersions. These pirogue outings make it possible to grasp the mangrove and its vital role without ever compromising the fragile balance of the habitat.