Cas Cay

Fourteen eager adventurers including Captain Mark and family loaded into Capt. Mark’s boat and Jack’s dingy and left Compass Point Marina for the Cas Cay Wildlife Sanctuary, an island that was donated to the government of the Virgin Islands in 1987 by its former owners.

After hopping out of our ships into knee-deep water, the group congregated around our volunteer lecturers Roy Watlington, Toni Thomas, and Renata……. Toni and Roy demonstrated edible sea purslane by having a snack and the more adventurous among us followed their example.

The first part of the hike was a sandy trail following the island’s perimeter. This took us to a rock fall area with a mixture of huge boulders, medium-sized rocks, and rocks pulverized to sand quality. The group proceeded to rock scramble into the area.

Roy filled us in on the geological history of the island, which is part of the oldest geological formation of the Virgin Islands, the Water Island formation. The magma from an undersea volcano was extruded at a depth of 5 kilometers maybe 108 million years ago (this is based on the oldest dated age of known rocks, it may have occurred even earlier). The rock mass from this extrusion was later brought to the surface by tectonic heaving. The workings of the undersea volcanic activity included many different mineral compounds which reacted differently when they were exposed to water. Furthermore, some of the compounds were never exposed to water: When the solidified magma from the volcanic eruption was pushed above the surface, outer layers of the magma peeled off, exposing the underlying minerals directly to air. The result of these events is an awe-inspiring array of colors and textures in a very small area.

Roy and Toni also explained the process of land extension. The red mangroves which populate the island produce propagules, which look like long beans from a distance. The propagules are dropped by the mangrove and fall wherever, including into the water, where they root and grow into more red mangrove. This process is encouraged by the build-up of coral rubble washed ashore by storms, which then creates an environment hospitable to the propagules. An excellent example is the developing land bridge of coral build-up between Cas Cay and neighboring Patricia Cay.

Black mangrove and red mangrove have different root systems. The red mangrove’s distinctive exposed prop roots grow above the water. Black mangrove roots stay underwater but produce air breathing pneumataphores (roots) that pop up above the surface of the water and supply the root system with oxygen.
Greater and lesser Antilles refer to the age of the geologic formations rather than to size. The Greater Antilles are older. They start with St. Croix and Virgin Gorda and go west.

After a period of leisurely explorations and research, the group returned to their vessels and then to Compass Point Marina. It was the time of day when sea birds were beginning to settle into the mangroves for the night. The activity and the light were stunning.