Sharing 40 years’ experience of working on mangroves – the generous forests of the tidal zone

Discovering mangroves

My enthusiasm for mangrove ecology started in a long house in the Gulf Province in Papua New Guinea. This huge structure was made entirely of mangrove timbers and thatched with fronds of a mangrove palm. Here I listened as my colleague in the Office of Forests negotiated with the traditional land owners for permission to conduct fieldwork. Young men from the village were detailed to observe and assist our team that was to weigh a huge tree within the forest. That sweaty teamwork was my introduction to the idea of biomass – the weight of living matter within a forest. I wondered what the young men would tell the village elders about our activities, but was hooked on mangrove forests after that!

Mangroves are trees that live in tropical tidal waters, where the salt and daily submergence prevents establishment of almost all other trees. Confusingly, but understandably, people also refer to forests of these trees as mangroves. In the last quarter of last century, a large portion of mangrove forest cover was lost due to conversion of these areas for aquaculture of prawns and fish. Encouragingly, in the current century, the value of mangrove forests has come to be more widely appreciated and mangrove loss has slowed with some areas of forest being re-established.

Celebrating the importance of mangroves

Mangrove forests are a vital part of the carbon cycle that buffers us from climate change.  They draw down carbon dioxide from the atmosphere and store the carbon in the leaves, branches and trunks of the trees, but as leaves and woody parts of the trees are shed leaves, carbon is transferred to in the sediment in which they grow and into coastal waters. Remarkably these forests can contain as much carbon in the trees as in rainforests do, but they store much more carbon than rainforest do locked up in the soil in which they grow. Plant waste travelling out on the tides supplies food to coastal waters. The forests also act as nurseries for fish and prawns that are caught in waters offshore. Juvenile fish feed and develop among the protection of roots and move into offshore when able to fend for themselves. Some, such as groupers, move to coral reefs. Mangrove roots stabilise shore sediments and also break up inrushing waves.

The underwater life associated with mangroves – Bonaire Credit : Ewan Trégarot

Mangroves and the work of MaCoBioS

Mangroves range from the northern end of the Red Sea to the North Island of New Zealand and flourish on calm subtropical and tropical shorelines in between. Surf shores are not suitable for mangroves. Though mainly located in the waters of continental Europe, the MaCoBioS project extends into the Caribbean with particular case study sites in Bonaire, Martinique and Barbados, where mangroves play an important role in protecting and feeding juvenile reef fish. In the Caribbean, mangrove forests survive cyclones while protecting the shorelines. Scars of hurricane track are visible in these forests many years after the event. Though much smaller in height and area covered than the huge forests of the Gulf of Papua, these Caribbean forests serve the island communities in numerous ways. They are particularly closely linked with the health of nearby coral reefs, act as key stepping stones for migrating birds, are recreational areas and also destinations for ecotourists. The challenge is to ensure the future supply of these ecosystem services, by taking account of the needs of this generous ecosystem in coastal zone planning.

Strong connection with associated ecosystems such as seagrass beds and coral reefs – Bonaire Credit : Ewan Trégarot

One of the pleasures of working with mangrove ecosystems is that those who do are natural collaborators who are committed to the cause of protecting these ecosystems. I hand over here to Ewan Trégarot to talk about the mangrove component of the MaCoBioS project.

Our experts are studying what are the effects of climate changes and anthropogenic stressors on mangroves and how those multiple pressures interact with each other’s. How can we use remote sensing to monitor the ecological condition of mangroves and the ecosystem services provided? What would happen to mangroves in the Caribbean in 2050 or 2100 given the current climate change predictions? Many questions remained to be answered, and hopefully, interesting elements of response will come up soon. Accordingly, remedial work will be recommended to foster the return of mangroves through replanting, restoring tidal circulation and minimising undesirable threats from urbanisation. There need be no losers if remedies are well planned.  

The generous forest of the tidal zone – Martinique Credit Ewan Trégarot

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