Forests on the Edge

Jahson Alemu, marine biologist, discusses the importance of mangrove ecosystems to the enhancement and protection of coastlines, and also to our future. This feature was first published in the Tobago Newsday on Thursday December 15, 2016
Follow Jahson on twitter: @jahson_alemu.

If trees are the lungs of the earth, mangroves must be the kidneys. Like botanical amphibians, mangroves live life on the edge. Uniquely positioned at the dynamic interface between land and sea, they are highly productive tropical coastal ecosystems comprised mainly of trees and shrubs capable of thriving in humid heat, amid choking mud and salt levels in which only a few plant species can survive (Duke et al 1998). If you’ve never seen a mangrove, picture a lattice of tangled tree legs rising up from brackish water. At one point in our history, mangrove forests were treated as wasteland considered only useful as dumps, and haven to bad spirits, jumbies, runaways and criminals.

Red mangroves (Rhizophora mangle) and intertwining prop roots in Bon Accord Lagoon. Photo by Jahson Alemu I, 2014
The mangrove swamp was avoided and condemned as breeding ground for disease, mosquitoes, frogs, snakes and other beasties the mind could imagine. At the same time, however, they were important sources of building material, firewood, medicine, food security (agriculture), homes for the poor, recreation and harbours for small boats. Today, mangroves have taken on additional meanings in our lives, where as well as the traditional roles, they now act as sources of revenue through ecotourism; major agents of soil stabilisation, coastal expansion and erosion control where interlocking roots stop land-based sediments from coursing out to sea. They build land, and their trunks and branches serve as barriers that diminish the erosive power of waves; and a climate regulators they store vast amounts of carbon that would otherwise be released into the atmosphere.

As discussed in last week’s article, they provide the unique requirements to create bioluminescent bays. But, probably one of the most well known roles of mangroves is as a home to wildlife (e.g. Scarlet Ibis) and nursery to fish and shellfish (e.g. spiny lobsters, snappers, tarpon and grouper). Altogether, these ecosystem goods and services have been valued globally at approximately US$32 billion annually, which translates to approximately US$194,000 ha-1 yr-1(Costanza et al 2014).

Despite their importance, our mangrove forests continue to be threatened and are rapidly declining. Significant alterations to mangrove forests in Trinidad and Tobago since the early 1970s have already resulted in an estimated 20% loss of mangrove forests due mainly to population growth and increasing development in coastal areas. Several examples illustrate these threats including decades of continued modification, built development encroachment: squatting and agriculture in the Caroni Swamp; the phenomenal shrinkage of the Friendship and Kilgwyn Swamps following necessary mangrove clearing for the Crown Point Airport runway expansion (IMA 1990); and development of the Canoe Bay Resort in 1980. Similarly, proposed resort and housing developments threaten the integrity of the Buccoo Bay mangrove forest. While there is growing recognition of the importance of mangrove forests, to date we have only managed to offer limited protection to three mangroves systems: Caroni Swamp, Nariva Swamp and Bon Accord Lagoon.

Coastal flooding and increased coastal erosion are but two of the major impacts we expect over the next 50-100 years if mangroves continue to shrink. In a recent review, the Institute of Marine Affairs described the state of mangrove conservation in Trinidad and Tobago as greatly challenged because of inadequacies in existing laws and institutional arrangements. If there is to be any meaningful slowing of the current rate of mangrove degradation and loss, an Integrated Coastal Zone Management (ICZM) approach is recommended as a means to promote coordination and clear distribution of responsibilities among the various authorities with jurisdiction over mangrove management.
The national bird, Scarlet Ibis (Eudocimus ruber), spends most of its life feeding and nesting in mangrove forests. Photo courtesy Charles J Sharp, 2014

 In spite of all these challenges, our environmental consciousness has increased tremendously over the last decade, and so too has our understanding of the role of mangroves in an uncertain future. Mangroves represent real opportunities for livelihood development (such as ecotourism, education, management); food security through the maintenance of juvenile fisheries stocks, biodiversity conservation especially of endangered species (e.g. goliath grouper/jewfish). In small islands such as ours, we are extremely vulnerable to climate change impacts, as such mangroves also represent important ecosystems for climate regulation and coastal resilience. Any development in or around these ecosystems should strive to have minimal impact on the mangrove forests, allowing them to thrive in their special relationship between the shore and sea.

Costanza R, de Groot R, Sutton P, van der Ploeg S, Anderson SJ, Kubiszewski I, et al. (2014) Changes in the global value of ecosystem services. Glob Environ Chang. 26: 152–158
Duke NC., Ball MC and Ellison JC (1998). Factors Influencing Biodiversity and Distributional Gradients in Mangroves. Glob. Ecol. Biogeogr. Lett. 7, 27  1996,
IMA (1990) Environmental Impact Assessment of the extension of Crown Point Airport Runway, Tobago. 123pp
Juman R and Ramsewak D (2013). Status of Mangrove Forests in Trinidad and Tobago, West Indies. Caribbean Journal of Science, 47(2-3), 291-304.
Juman R and Hassanali K (2013) Mangrove Conservation in Trinidad and Tobago, West Indies (pp. 35-64) in (eds) Gleason G and Victor TR (2013). Mangrove ecosystems: biogeography, genetic diversity and conservation strategies. Environmental research.


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