Know Your Islands

The shallow, warm, crystal clear waters surrounding the Cayman Islands have provided us with some of nature’s most spectacular marine life, none more noteworthy than our breathtaking coral reefs. For hundreds of years, Caymanians depended on healthy coral reefs to provide food, building materials, medicines and even decorative objects. To this day, our coral reefs are integral to our island economy thanks to their contribution to tourism and fisheries. In addition, they play a critical role in protecting the shore from storms and hurricanes.

Although sometimes viewed as a separate entity, coral reefs are a vital part of a vast inter-connected marine ecosystem that also includes seagrass beds and mangrove wetlands. Each system depends heavily on the others, resulting in a tightly integrated and finely balanced marine environment. It is hard to imagine the massive reef structures and reef walls as fragile, living entities, but coral reefs are extremely sensitive to external pressures and over-exploitation. The mucus, or ‘skin’, that forms a layer over corals can be damaged simply by the touch of a hand or contact with a snorkeller’s fin. Once damaged, the living layer of tissue is exposed to bacteria, which can prove fatal to coral.

Coral reef structures are actually built from the skeletons of tiny creatures living in colonies. A closer look at the colourful colonies will reveal thousands of tiny bumps, called polyps. Each of these polyps is an individual coral animal, all of which join together to form a coral colony. Most coral colonies start life as a single polyp, no bigger than a pinhead that drifts with the ocean currents to settle on a suitable surface, such as a bare rock bottom. Once settled, the newly established coral polyp begins to grow, laying down a skeleton by extracting calcium carbonate from the surrounding water and budding off a new, individual polyp identical to itself. Continued budding is the mechanism for increasing the size of the colony but not, in general, producing new colonies. As this process repeats itself, time and time again, over many thousands of years, so the tremendous reef formations that can be found in Cayman, have been formed.

As well as budding, coral can reproduce sexually. This results in the formation of a free-floating larva, which, when settled, starts developing as a new colony. In the Caribbean, the main spawning period is long, lasting from July through September. During this period, corals release sperm and eggs at night using the moon as their cue to ensure they spawn together. Fortunate night divers can sometimes witness the milky white releases.

Corals feed at night by stretching out their tentacles to capture tiny animals suspended in the water column. Coral tentacles contain specialised cells called nematocysts, which act like poison darts to paralyse the prey which is then passed to the coral’s central mouth. During the day, they withdraw their tentacles into a cup-like skeleton and are fed by algae (single cell plants) residing within their tissue. The algae use sunlight along with the coral waste products to make food for themselves and the corals. The corals, in turn, give the algae nutrients they need to survive and provide a home. This type of mutually beneficial relationship is called symbiosis. This relationship is especially important for coral growth around the Cayman Islands as tropical waters are typically nutrient poor and food for corals is scarce. Without the algae, corals would not survive. Interestingly, it is the algae that are responsible for giving each coral its beautiful colours.

For more information on the Trust’s various historic and natural topics, please visit our website, particularly the Information Sheets drop-down menu on the bottom left. Photographs from the National Trust Archive.

Grow Cayman Plants and encourage Cayman Wildlife! For more information, to share your knowledge or if you would like to get involved with the many activities in the National Trust’s Know Your Islands Program, please visit www.nationaltrust.org.ky, www.caymanwildlife.org or call 949-0121. The weekly column from the National Trust is submitted by Marnie Laing, Education Programs Manager at the Trust.

Last week’s answer: The two mile Mastic Trail was constructed in the mid 1800s by William Watler Jr. to provide access to his farmland in North Side from his home in Bodden Town.

Trivia question: When did the first cruise ship visit the Cayman Islands?

Look for the answer in next week’s feature!