St. John Environment: Salt Ponds

St. John Environments: Salt PondsSalt Ponds
The complex balance of land and sea environments supports the incredible natural beauty of St. John, the white soft sandy beaches, the crystal-clear water, the colorful coral reef, the fish, the sea creatures, the exotic tropical foliage, the birds, bats, butterflies and every other living thing. One of these environments that is often overlooked is the salt pond.

How Are Salt Ponds Formed?
Most of the salt ponds of St. John were once bays, open to the sea. Coral reefs develop naturally around the rocky headlands that jut out and define bays. In time the reef may extend out from the headland toward the center of the bay. When this happens simultaneously on both headlands, the bay begins to be closed off. As the reef matures, the top of the reef rises toward the surface of the water. Strong storms and hurricanes carry sand, rocks and pieces of broken coral and pile them on top of the reef creating a surface platform above sea level. Meanwhile heavy rains and gut washes cause sediments and soil from the land to collect on the protected side of the platform facing the land. With the help of salt tolerant plants, such as mangroves, to secure these sediments, the platform will gradually get larger and denser. A salt pond is born when the spit of solid land builds up enough to close off the bay from the sea.

How Do Salt Ponds Protect the Coral Reefs?
During heavy rains, water runs down valleys and hillsides into guts leading to the low flat areas just inshore from the central portions of the bay. Salt ponds are generally found in these low-lying areas and serve as buffers between land and sea. The salt pond acts much like the septic systems used by many homes on St. John. Water flowing down the valley picks up soil, organic debris and possibly dangerous pollutants. This mix is deposited into the salt pond instead of washing directly into the sea. The sediments settle to the bottom of the pond and the now purified water can seep through the filter-like sand and coral rubble wall of the pond into the bay without causing turbidity or cloudiness.

The Salt Pond Environment
Salt ponds are extremely hostile environments for living things. Depending on the salt pond’s location and on conditions such as temperature, rainfall and windiness, the water within the pond can range from almost fresh to a super-saline solution five times the saltiness of the sea. Add to this the high temperature that the water can reach during sunny dry afternoons and you would think that nothing could survive there. Nonetheless, the salt pond is inhabited by such creatures as brine shrimp, crabs, insects and insect larva, which provide the basis for a food chain. Birds, waterfowl and bats that feed on these organisms are attracted to the pond environment and several species of birds tend to make their nests nearby.

Birds commonly found at or near St. John salt ponds include herons, sandpipers, yellowlegs, and pin tail ducks. In addition, certain fish, such as barracuda, tarpon, mullet and snook, attracted by the brine shrimp, sometimes make their way into salt ponds that have an opening to the sea. In some parts of the world the brine shrimp from salt ponds are harvested commercially for tropical fish food, and the larva produced by brine shrimp eggs has been marketed (particularly in comic books) as “sea monkeys”.

Salt ponds can be smelly and murky and in the past they were indiscriminately dredged, drained, filled or opened to the sea. As a result they have been disappearing from the Virgin Islands at an alarming rate. Fortunately, they are now protected under the territorial Coastal Zone Management department and also under federal legislation, which means no filling, opening or dredging.

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