Know your islands
The majority of Grand Cayman lies less than 10 feet above sea level.
The island is flat; if you are on a boat on the North Sound, you can count the number of cruise ships in the harbour on the other side of the island.
For some, the more exhilarating scenery of the island lies below the waves.
The Wall is a steep cliff underwater marked by various geological features that is part of and extends around each of the Cayman Islands.
If you are qualified in technical diving using mixed gases, you can visit an area concentrated at about 250 to 330 feet continuing along the western Wall of Grand Cayman.
This area is referred to as the sponge belt. Sponges are not plants, but a group of the simplest of multicellular animals. The group has an extraordinary range of textures, shapes and colors and its showcase seems to be situated in this sponge belt zone.
The accompanying photographs were generously provided by Courtney Platt www.courtneyplatt.com.
Sponges are part of the sessile benthos which is organisms that live on the seabed and do not move. Having no head, mouth or internal organs; sponges pump large volumes of water through their flexible bodies that consist of a series of water canals acting as filters for nutrients.
Sunlight and nutrients are essential for most marine production and is especially true for this environment.
The photic or sunlit zone is only about 330 feet deep. Many of the materials necessary for growth are removed by algae and are therefore found in low concentrations in surface waters. Such algal and animal material descends below the sunlit zone and decay.
During this process nutrients are being re-released and in the absence of light at depth, they are not used and therefore become concentrated.
This creates a source of nutrients below the surface waters. The zone of 160 to 330 feet creates a boundary for this reservoir between the nutrient-poor sunlit waters and the thermocline below.
The inhabitants at this depth around Grand Cayman reflect the description in Alice in Wonderland when she found her surroundings grown to an exaggerated size.
Immense elephant-ear sponges and brilliant red, yellow and orange rope sponges entangled in large masses help create a dense forest-like environment. Clusters of luminous white tube sponges extending 9 feet from the wall beckon visiting divers.
Beyond the rubble field of George Town Harbour, precariously hiding from cruise ship anchors at 250 feet, is a giant elephant-ear sponge that is 18 feet from top to bottom. Sediment that has moved from the slope of the wall covers this incredible animal but does not hide its awesome magnitude.
Long extending arms of red rope sponge are contrasted by the deep blue water.
The light penetrating through the water is increasingly absorbed to these depths. Wavelengths at the long or red end of the visible spectrum are the first to be absorbed, followed by the disappearance of oranges and yellows. Orange, lavender and shades of reds and pinks crawl across each other once awakened by diver’s strobes and lights.
Our marine environment has an incredible diversity of life, including deep ocean ecosystems and communities. There is an interconnection between all living things, and we must respect all life, big or small, deep within our forest or deep within our sea and do what we can to protect it.
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]