Tag: coquina

The Clam That Changed the World – Chapter 5

Hardly anyone thinks that clams changed the world. Most are benign, industrious critters toiling away in the sand or resting quietly in the sea. If we do consider them, it’s mostly because many are edible and some produce valuable, nacre-coated irritants worn as fashion. Perhaps the most famous bivalve in the world is the one that supports Venus in Botticelli’s legendary painting, The Birth of Venus. Botticelli depicts the Roman Goddess of beauty and love using the shell as a mode of transport as she arrives on land, blown by the winds. Although unrealistic as a way to travel, Botticelli’s shell does fit the classic image of a bivalve, something trod under foot.

Castillo de San Marcos, courtesy of National Park Service

Thus some find it odd that a bivalve, in particular a much smaller clam than the one that carried the lovely Venus, was seminal to the early history of colonization of North America. Carolina governor James Moore was the first to discover the power of the clam when he lay siege to the Spanish town of St. Augustine, Florida, in 1702. Moore attacked St. Augustine with 800 men, which forced all of the town’s residents into their recently completed fort, known as Castillo de San Marcos.

For six weeks, Moore bombarded the Castillo, but with no luck. Cannonballs either bounced off of or stuck in the fort without breaking the walls. What was the miraculous building material? It was an unusual variety of limestone called coquina (Spanish for “little shell”), which outcrops along the northern Florida coast. It formed 110,000 years ago as billions of bivalves accumulated on beaches. By far the most abundant bivalve is the coquina clam, Donax variabilis, the clam that changed the world.

Moore eventually abandoned his nefarious plans and retreated back to Carolina. Thirty years later the English tried once more to take St. Augustine. Again they failed because of the coquina, leading one British soldier to express “[it] will not splinter but will give way to a cannon ball as though you would stick a knife into cheese.” Without the clam, one can argue that the English would have succeeded in invading St. Augustine, driven the Spanish out of Florida, and who knows how the world would have turned out.

But because of the clam, no armed force ever took St. Augustine. The Castillo still stands, a wonderful tribute to the power of stone to influence architecture, history, and politics.

Plants and Stone: Castillo de San Marcos

I wanted to follow up my previous posting on plants and geology and turn a little closer to home, though this posting features a building more than 3,000 miles from my home. In St. Augustine, Florida, the Castillo de San Marcos also functions as nursery. Started in 1672 and finished in 1695, the Castillo is the oldest fort in the United States. It is now owned by the National Park Service.

The Castillo was built by the Spanish to help defend Florida. They only had one type of stone to use, coquina quarried a half mile away on Anastasia Island. For those not familiar with coquina, I liken it to a granola bar, except that shells, broken and whole, have replaced the oats. Coquina is so soft that cannonballs fired at the fort either bounced off or sank into the stone.

A botanical survey conducted in 2003 and 2004 found 56 plant species, ranging from moss to elm, growing on the coquina walls. Cyanobacteria, nematodes, fungi, and diatoms have also established themselves on the coquina. It is quite a cozy place.

A fern garden growing in coquina

The best place to see to plants is down in the moat, on hanging gardens rich in ferns, grasses, and forbs. The gardens cover the walls every 30 feet or so, wherever water drips from scuppers that drain the courtyard roof. And the plants don’t just grow outside. In one of the courtyard rooms in the 1930s, the park service used to maintain a “fern room” almost completely covered in maidenhair fern. Now only a few ferns grow in this room.

Dark, hanging gardens of the Castillo

The walls are plant rich because the coquina is shell-rich. The heterogeneous mix of shells make a Swiss cheese-like surface, where seeds can land and get established. Water also accumulates in the cavities, further turning the coquina into a nursery.

Despite the beauty of the flowers, maintenance workers at the Castillo constantly pull out the plants by hand. They don’t want the roots to get established and destroy the fort. Cleaning the walls of plants takes about six months, though of course they can’t get it all clean and little fields of color always festoon the mighty fortress.