Features

Islands of the Sea

A Natural History
Story and Photos by Kathleen McNary Wood

A tiny chain of emerald green islands sit poised in a seemingly endless and vast deep-blue sea surrounded by
a thin fringe of crystal-white sands and shallow turquoise banks. Like glittering beads of a necklace, each color represents a precious jewel of natural history that makes these islands a paradise on earth. The deep-blue seas are where the islands began and hold the untold mysteries of their past and future. The crystal-white sands, like sugar coating a delicious treat, are worth their proverbial weight in the now burgeoning tourist industry. The unbelievable turquoise waters delicately gracing the boundaries of the chain contain diverse tropical reefs, productive estuaries and mangrove communities that are the breadbaskets of a thriving marine ecosystem. And finally, although certainly not least, are the emeralds themselves–rare tropical dry forests that remain much as they have for thousands of years.

In the beginning there was nothing but a blue sea and sky, and the ancient earth shifted moving sea floors to shallower depths where they could capture the scattered underwater light of the sun. The sun warmed the sea, and the light made it possible for algae and corals to colonize the shallow continental shelves eventually forming giant fringing reefs teeming with life. This was about 135 million years ago when the earth’s land masses were ruled by dinosaurs, but the islands themselves still did not break the surface of the vast expanse of blue.

Over eons of time, the fishes, corals, algae and other organisms engaged in the constant cycle of life and death, but as they lived and died, their legacy was left behind in the form of tiny calcium carbonate skeletons and bi-products. For ages and ages, the remnants of these early marine lifeforms collected in the troughs between reefs and on the shallow banks surrounding them, gradually building up sediment to form shallow turquoise bays.

Birth of an Archipelago
Then the earth cooled. Glaciers of mammoth proportions blanketed Eurasia and North America, drinking up stores of the oceans’ waters and causing the sea levels to recede. As many as four times, the great oceans rose and receded again, and then, about 75,000 years ago, during the last great ice age known as the Wisconsin, from the receding tide, the coral reefs and shallow bays emerged out of the water to form dry land.

The water receded slowly at first, revealing only wisps of sandy spits that disappeared each day with the rising tide. The same tides brought the first inhabitants of this new ephemeral and inhospitable place neither of the land nor the sea. These were ingenious trees that traveled the oceans of the earth in ready-to-grow packages called propagules. When they met the edge of the land, they put down roots and sprouted leaves to form forests of red mangroves (Rhizophora mangle) bridging the space between the new land and the sea.

Once the coastline was secured, other species of mangroves–Black (Avicennia germinans), White (Laguncularia racemosa) and Buttonwood (Conocarpus erectus) established themselves. Into their expansive root systems came the creatures of the sea. Providing food, shelter and protection for juvenile marine species, the mangroves soon became an important link in the marine food web, but they were also critical in the development of the land. Long-legged birds took advantage of the bounty of the mangroves and began to make their homes among them.

Thousands of years later, these keystone mangrove species continue their legacy, standing guard along the coastlines and protecting the fragile and ever-changing boundaries of the islands and their origins.
On the currents of the seas, tiny crystals of calcium carbonate known as “aragonite” drifted until they met the edge of the land and the sea where the mangroves grew. They deposited by the billions until miles and miles of brilliant white sand stretched where once there was only blue.

The seas continued to recede. At their lowest levels, the oceans were a monumental 400 feet below their current levels. This was a time when the islands flourished. What today comprise the numerous underwater banks of the island chains became acres and acres of flat lands. Ancient coral ridges and dunes became veritable mountain ranges of up to 600 feet in height. The islands were massive land masses extending their boundaries to the edges of the neighboring islands of Cuba and Hispaniola.

The Great Migration
It was then that an extraordinary mass migration began. Pioneers began to make their way to the new shores carried on the wind, currents and sea. The fertile beginnings of plants sailed the sea in buoyant pods, or flew with wings on the winds, or deposited in the dung of migrating birds that happened to pass by.

To these early inhabitants, the islands of the sea were an inhospitable place. There was no topsoil save the organic, salt-saturated muck that once lined the bottoms of ancient bays. Fresh water was a scarce commodity, and the sea and wind constantly drenched the land with fresh supplies of damaging salt spray. Many of the new arrivals did not survive at all. Those that did survive were able to adapt.

Island Biogeography
Perhaps it was at this time that a distant relative of Island Heather (Limonium bahamense) first made its way across the sea to settle. Confronted with the harsh environment, these delicate herbs changed themselves genetically in order to survive in this perilous new world. Today, this species has evolved into a plant that exists in a limited habitat only at the edges of salt ponds and low-lying salty flood plains. It exists nowhere else on earth.

Isolation and time–plenty of time–are the islands’ secrets. Islands throughout the world encompass only a small fraction of the earth’s surface, but they contain within their boundaries about 1/6 of all plant species.

This is one of nature’s ironic twists. The more treacherous the terrain, the more likely it will be that organisms will mutate and evolve to form endemic or unique species that are limited to a restricted geographical area. In many cases, they become so specialized that they cannot really exist in any other place on earth. Environmental change, both natural and unnatural, has led to a mass extinction of endemic species worldwide. Islands have been particularly vulnerable.

The clearance of land for development, dredging of salt ponds and salt flats to make way for marinas and general human interference could wipe out many plants unique to these islands and contribute to their extinction. This is the way with islands.

And, plants aren’t the only organisms affected by this phenomenon. In fact, many classes of organisms are subject to the mysterious evolutionary forces of island biogeography. Since the millions of years since their creation, islands have been the home to several unique species. We are all familiar with the tragic plight of the Dodo. This now extinct bird stands as a symbol for the creative forces of islands. It also stands as a testament to their vulnerability.

Other Pioneers
The sea brought forth other pioneers as well. Reptiles, insects and small mammals cast away from their native lands by tropical whirlwinds and storms grasped for life to floating rafts of driftwood and other debris. They sailed aimlessly on the sea until by chance, their unintentional crafts collided with the new land and they were able to disembark.

For others, it was easier. Birds and bats had the gift of flight and made their way easily to the uninhabited new land. Others took advantage of land bridges that formed at the edges of the massive ice age islands connecting them to larger islands to the east and south.

From North America, Cuba, Hispaniola, the Antilles and even as far away as Africa, the migrants came on the land, sea and air. As treacherous as the migrations were, this was not the end of their struggles.

Long ago on these islands of the sea, giant land tortoises and strange mammals known as Houtia roamed the land foraging on the fruit and leaves of island vegetation. Long-tailed tree iguanas climbed through the vegetation, basking in the treetops and seeking out the tender young shoots of edible leaves.

It is not known why these species no longer thrive here, but their fossilized remains have been found scattered throughout the islands in several Lucayan archaeological sites. This leads some to believe that the early human inhabitants of these islands, the Lucayan or Taino Indians, hunted them. Whatever the reason, they were not able to adapt quickly enough to survive in the changing world around them. The natural history of islands is also a history of extinction.

Remnants from the Past
Yet many animal relics from the past did survive and still remain today in the islands living much as they have for thousands of years. The Rock Iguana is a living testament to the evolutionary history of these islands. This species, Cyclura carinata carinata, evolved from an earlier form into a creature that exists nowhere else. Having formed in a sheltered environment free from large predators, their fate is now uncertain. Although they have survived the ecological battles of survival of the fittest, tropical tempests and other natural disasters, they stand no chance against a simple domesticated dog or cat.

Other endemic creatures are the Pigmy Boa Constrictor, Curly-tail Lizard and Dead Leaf Butterfly. Each of these species is found only in this region and nowhere else on earth. Each of them once made the perilous journey across the seas, found their way to these isolated isles and changed genetically over time in order to adapt to their new environment.

Secrets of the Emerald Green Forests
Over time, the new pioneers established themselves and began the terrestrial cycles of growth, reproduction and death. Decaying biomass gradually, over thousands of years, formed thin soils that enabled more complex plants such as trees to get a foothold in the changing landscape. Seasonal rains came and went, making the growing periods short and difficult. Only the species that were able to withstand long periods of drought were able to gain a foothold. Then, very slowly, vast emerald green forests, dwarfed like natural bonsai gardens and perfectly adapted to the harsh island climate, grew where once there was only water, sun and a deep blue sea.

A tree stands in the forest. It has witnessed eons of change, and yet the forest still stands. Perhaps it is a Lignum Vitae (Guaiacum sanctum), carried once centuries earlier as a red, juicy seed in the beak or belly of a traveling bird searching for sanctuary from the encroaching cold from the north. Maybe it is a stately Mahogany (Swietennia mahogoni), whose winged seeds travel on the winds far and wide in search of suitable soils in which to sprout. Maybe it is a rare Caribbean Pine (Pinus caribbaea var. bahamense). Found only in this archipelago and nowhere else on earth, it keeps the mysteries of its origins a secret that is told only in the whispering of the wind through its needles.

It could be one of countless trees that make up the vast and untouched forests of the islands, unique in their composition, living and flourishing for thousands of years and withstanding the rising and lowering of the seas, hurricanes of incredible force, fires and the actions of man.
One day, the earth will warm again, melting the polar ice caps and unleashing the seas, which will follow with increasing tides. Once again, the islands of the sea will revert back to their origins to become flourishing underwater reefs and bays.

Until that time, we are the stewards of this precious moment in time and the unique organisms that inhabit these islands. Beautiful by nature and continuing to change and evolve with each rise and fall of the tides, these islands borne of the sea are the Turks and Caicos.



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