I remember the day when I first arrived in the BVI, fresh out of university and ready to save the coral reefs and marine mammals of the world. I vaguely recalled one of my professors mentioning mangroves in my biological oceanography class, but mangroves didn't sound nearly as exotic as the array of marine life found on coral reefs, nor as magnificent as whales, the leviathans of the sea.
Mangroves are unique plants which are able to grow in warm, salty environments. Although they do not require salt water to grow, mangroves are able to grow in places which are too salty for other plants. Their roots take up salt water which is then transformed into fresh water by the removal of salt. The salt is excreted by the plant through the tiny pores found on its leaves. Mangroves are also unique in that their seeds germinate while still attached to the parent tree. Once the seed is a certain size, they drop to the ground where they take root and eventually grow into new mangrove trees. Some seeds are carried away by seawater to other shallow areas where they will form a new stand of mangroves.
Three types of mangroves can be found in the British Virgin Islands. The most common and easily identified mangrove is the red mangrove (Rizophora mangle) which extends its prop roots out into the water in order to provide support for the plant. The black mangrove (Avicennia germinans) is usually found in muddy areas behind the red mangrove where it uses snorkel-like pneumatophores to obtain oxygen for the plant. Finally the white mangrove (Laguncularia racemosa) lingers behind where the soil is the saltiest, yet the driest. The most distinctive feature of the white mangrove is its round, thick and waxy leaf which helps to reduce water loss to the surrounding air.
Having learned this much about the mysterious unheralded mangroves, my respect for these hardy plants increased a notch. Then I learned about the important role these plants play in our marine ecosystem. Growing along the shoreline, mangroves form a barrier between the land and the sea. This barrier is important in protecting the shoreline from high waves and subsequent erosion. The mangroves are also able to protect the sea from the land. During heavy rains, silty runoff from the land flows down the hillsides to the water. The intricate web of mangrove roots along the shoreline is able to filter much of the silt out of the runoff, thereby preventing the seawater from getting cloudy. This is very important for protecting nearby coral reef and seagrass, which require clear water and sunlight to grow.
Although not always apparent at first sight, there are many animals which can be found within a mangrove area. Small crabs can be seen scurrying from hole to hole among the mud and roots of the mangroves, while herons, pelicans and osprey fly overhead looking for food, usually fish. Underwater, a diverse collection of animals can be seen, including mangrove oysters and colorful sponges attached to the roots of the red mangrove, as well as juvenile lobsters and a varied collection of juvenile fish, which seek food and shelter from predators. These fish and shellfish are important for sustaining a successful fishery in the BVI.
Mangroves not only grow along shorelines. They can also be instrumental in the formation of salt ponds, which also help protect the ocean from silt and sediment. For the most part, salt ponds are former bays or parts of a bay that were once open to the sea, but over time were closed off by reef or mangrove growth. Once the bay is closed, the salt pond begins to act as a sink for silt and sediment that runs down the hillsides during heavy rain.
I have spent many a relaxing afternoon on the edge of a salt pond, fringed with mangroves, taking photographs of the diverse collection of wading birds that can be found feeding on the microscopic animals of the pond. Flamingos can be observed in the ponds of Anegada where they filter the water from brine shrimp. Josiah's Bay pond serves as host for Black-necked Stilts and wintering White-cheeked Pintail Ducks. A variety of herons, including Yellow-crowned Night Herons, Great Blue Herons and Green-backed Herons can be found feeding in the ponds of Fat Hogs Bay. The salt ponds of Beef Island also provide excellent photo opportunities for Wilson's Thick-billed Plovers and Little Blue Herons, to name a few.
Over the years I have been humbled by my recognition of the importance of mangroves and awed by the variety of wildlife found within their fold. They are neither more nor less important than the coral reefs and seagrass beds that surround us. Rather they all play an equally important roll in maintaining a healthy marine ecosystem.