Know Your Islands: Mangrove Wetland key to ecology

Grand Cayman’s Central Mangrove Wetland is the ecological heart of Grand Cayman.  

It is critical to so many important natural processes that the National Trust for the Cayman Islands considers its long-term protection to be one of the fundamental requirements for the well-being of future generations in the Cayman Islands.  

About 1,500 acres of the Central Mangrove Wetland is protected through the Marine Parks Law, forming part of the Environmental Zone, which has been in effect for Little Sound and its fringing mangroves since 1986. Efforts are under way to increase the area of the wetland under protection, through conservation land purchase.  

The Central Mangrove Wetland is part of a large-scale water flow system, filtering and conditioning the surface water and shallow ground water that flows into North Sound. Both by constant tidal flushing of the mangrove fringes and by occasional massive overflows of accumulated rainwater from the entire Central Mangrove basin, the wetland provides a flow of nutrients into North Sound.  

These nutrients form the base of a complex food chain from the Turtle Grass and shrimp mounds in Little Sound, through to the snappers and lobsters that move from the mangroves to the reef. The entire living system of North Sound is inextricably linked to the Central Mangroves, and would collapse if the wetland was destroyed.  

Natural state 
of the Wetland 

The wetland covers a total of about 8,500 acres, still almost entirely in its natural state.  

Except for areas of open water, it is covered by a canopy of trees, which absorb sunlight and radiate part of that energy as heat, warming the air near the leaves. The same air also becomes saturated with water vapour, evaporating from the leaves’ breathing pores and from the ponds below.  

Warm air is less dense than cooler air and rises in a complex pattern of convection currents. Saturated air rising above the Central Mangrove Wetland in this way forms rapidly developing clouds, which are carried west by the prevailing winds and dump rain over the central and western districts of Grand Cayman.  

This process is believed to contribute a large part of western Grand Cayman’s rainfall, which is 40 per cent greater than in the eastern districts. Without the Central Mangroves, George Town and West Bay could be almost as dry as East End but without the benefit of an unspoiled groundwater lens to keep the trees healthy and the well water fresh.  

Impact on agricultural land 

The Central Mangrove Wetland is surrounded by some of Grand Cayman’s best agricultural land, and also by a system of fresh water lenses. The wetland helps to hold back rainwater flowing towards the sea from higher land, and so maintains the fresh water lenses and holds up high fresh water tables in agricultural land. Mangrove canalisation and development in western Grand Cayman has already shown how vulnerable our agriculture and groundwater supplies are to the destruction of neighbouring wetlands.  

West Indian Whistling Duck, Grand Cayman Parrots, Snowy Egrets and many other native birds depend on the Central Mangrove Wetland for food, shelter and as a place to breed. Various crab species, smaller crustaceans – some of which have only recently been described by scientists – and countless species of insects and other invertebrates inhabit the wetland, along with fish, Hickatees, agouti and many other animal life forms. The Red, Black and White Mangroves are joined by Buttonwoods, and a variety of dry land trees like Mahogany and Wild Fig have also gained a foothold in the more remote areas of the Wetland, where fresh rainwater sometimes floats on top of the salty groundwater.  

 

This column was submitted by the National Trust for the Cayman Islands. The National Trust can be contacted at 749-1121 or by emailing [email protected] 

Cayman whistling duck

Whistling duck

Cayman Agouti

The agouti was introduced to Grand Cayman in the 1900s.
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