MANGROVE SYSTEM IS IMPORTANT
About the article
This is a digitised version of an article from The Cayman Compass's print archive. Occasionally, the digitisation process introduces transcription errors, or other problems.
See the article in its original context from June 1985.
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Assistant Scientific Officer, Natural Resources FOR many people the term "mangrove swamp" brings to mind a hot, fetid place where mosquitoes breed in unbelievable numbers and all manner of creatures lurk in the dark forbidding water. Consequently, the numerous uses and the value of the mangrove system are largely unappreciated. Environment week affords the opportunity to highlight this unique and often misunderstood ecosystem.
Grand Cayman, with a total area of 197 sq. kilometers (76.4 sq. miles) has approximately 108 sq. kilometers (42 sq. miles) of mangrove swamp where three species of mangrove trees occur. These are: the red mangrove (Rhizophora mangle), the black mangrove (Avicennia germinans), and the white mangrove (Laguncularia racemosa).
These trees have several physiological and structural adaptations which enable them to flourish in an environment characterized by high temperatures, widely fluctuating salinities and shifting substances of low oxygen content.
One of these adaptations is the remarkable root systems of the red and black mangroves. Unlike most higher plants, mangroves usually have highly developed aerial roots in contrast to modest root systems below ground.
The red mangrove, which may attain a height of 25 m. (80 ft.), has a system of "prop" roots which extend a metre (3 ft.) or more above the surface of the soil and contain many small pores called lenticels. At low tide the lenticels allow oxygen to diffuse into the plant and down to the underground roots by means of small open passages.
Black mangroves, which may grow to 20 m. (64 ft.), have small air roots (pneumatophores) which extend vertically upward from the underground roots to a height of 20-30 cm. (8-12 m.) above the soil. These small air roots resemble hundreds of tiny fingers sticking out of the mud underneath the tree canopy. At low tide oxygen travels to living root tissue by means of these tiny fingers.
The white mangrove, having neither of these types of roots, uses lenticels in the lower portion of the drunk to obtain oxygen.
As well as being extremely fine-tuned to their environment, mangroves play an important role in coastal stabilization, fishery production and in the maintenance of critical habitats for many threatened or endangered species of birds.
The prop roots of the red mangrove act as shoreline stabilizers and wave barriers. These trees, which typically fringe the coastline, also serve to dampen storm surges and high winds associated with tropical storms and hurricanes.
In addition, the prop roots afford a relatively protected habitat which is particularly suitable for many juvenile fish and invertebrates. The nursery value of the prop roots for juvenile spiny lobsters (Panulirus argus) has been well documented by researchers and, according to their published information, the juveniles may remain in close association with the prop-root community for as many as two years. Universally acknowledged as one of the most productive natural systems on earth, the mangrove ecosystem provides the basic energy source of the detritus-based food web on which many juvenile mollusc, crustaceans and fish are dependent. However, activities like dredging, carried out in a mangrove area, pose a threat to the well-being of the mangrove-associated fisheries in that the increased sediment load of the water can severely reduce the net primary productivity upon which the fisheries depend. The condition or well-being of mangrove associated fisheries is dependent, therefore, upon the health and survival of the mangrove system itself.
Because mangroves present a diverse structural habitat, they also harbour a great variety of bird life. Herons, egrets, ducks and gallinules, as well as the endangered Cayman parrot, are fairly common sights in the Cayman swamps. It has also been shown that mangroves play an extremely important role in providing a wintering habitat for migrant birds of North American origin. The birds, in turn, are part of the complex mangrove food web and some contribute significantly to nutrient cycling in the coastal zone.
At no cost to man, mangrove swamps provide shoreline protection, support extensive coastal food webs and provide habitats for valuable fish, birds and many crustaceans and mollusc.
Today in Cayman we are faced with the problem of an escalating rate of destruction of swamp land due to increased developmental pressure. With greater affluence in our society and an increasing population, it becomes harder to assign relative values to leaving a mangrove swamp in its natural state or to using it for luxurious waterfront dwellings.
The time has come, therefore, for us all to realize that although a project involving mangrove destruction will bring financial benefits to individuals in the short-term, undeveloped mangrove swamps offer benefits to all, and will continue to benefit our children and grandchildren whose rightful inheritance of a rich natural environment depends on our choice of priorities now. (GIS)
