Know your islands
Where does Cayman’s beautiful white sand originate?
Believe it or not, from a colourful parrotfish and green algae!
From a distance, all sandy beaches look the same. But if you take a closer look, you will find they are all very different. Every grain of sand is unique in colour, texture, and shape, depending on what it is made from and where it lives on the beach. Sand is created from either rocks or sea animal remains, such as fragmented shells.
The floury soft coral sand found on the majority of Cayman’s beaches comes, almost entirely, from the coral reef community. This type of sand is biogenic – sands made of the skeletal remains of plants and animals. This is the main reason why our sand is so much finer and softer than the sand found on most continental beaches, which comes from terrestrial sources such as weathering rocks.
Most of our sand is created by wave and current energy acting on the coral reef as coral, calcareous green algae (algae with a hard exoskeleton), the shells of various sea creatures and sea urchin spines are gradually broken down into sand sized grains. Calcified green algae, particularly the Halimeda spp., are especially important as a major contributor of marine sediments.
The white sand is largely composed of the sun-bleached and eroded calcium-carbonate remnants of calcareous green algae. This calcified sand is deposited from natural expiration and consumption by some marine animals, such as the sea urchin species Clypeaster rosaceus and parrotfish.
Reef grazing fish, such as parrotfish, produce a significant amount of sand found on the beaches. Parrotfish get their names from their parrot-like mouths and they have strong teeth that resemble a parrot’s bill. These strong, sharp teeth allow parrotfish to scrape algae from rocks and corals. Parrotfish also bite off pieces of coral, grinding up the coral ‘skeleton’ to eat the tiny coral polyps or algae. But the parrotfish can’t digest the ground-up skeleton therefore this passes through their digestive systems to be excreted as ‘sand’! A single parrot fish can produce tons of soft white sand during its lifetime.
Parrotfish are not shy and are regularly seen while snorkelling or diving. Often you can hear the sound of their beaks scraping against the coral before you even see them! You may even see them relieving themselves of the indigestible portion of their meal in the form of sand that will settle slowly to the bottom of the sea.
Protect 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, or contact [email protected] or 949-0121.
The weekly column from the National Trust is submitted by Marnie Laing, Education Programs Manager at the Trust. The Trust can be contacted at 949-0121 or via email at [email protected].