The mangroves of Salt River Bay, St. Croix, US Virgin Islands, face a new challenge
By Amparo Pikarsky
Like giants dipping their toes into the briny sea, tall red mangrove trees appear to wade in the waters of Salt River Bay, standing on half-submerged roots that tangle all around them. Up to fifty feet high, these formidable titans cluster at the edge of the water protecting the land and the bay from each other: acting as powerful sentinels that shield the land and its inhabitants from waves, wind, hurricanes and tsunamis, and keeping natural contaminants from reaching the water. Mangroves filter solid waste, bacteria, fertilizers and pollutants and provide a place for silt to accumulate, so it does not reach the water and make it too cloudy to absorb sunshine—which is so essential to native sea grasses and coral, and the marine life, bioluminescence, and endangered species that co-exist in Salt River Bay.
Mangroves play an integral part in creating the mangal, or ecosystem, that is home to the unique diversity of life forms in Salt River Bay National Historic Park and Ecological Preserve in St. Croix, U.S. Virgin Islands. The park, which measures 145 hectares (approximately 358 acres), currently includes 19 hectares of mangrove forest— the largest remaining mangrove forest in the U.S. Virgin Islands. Its footprint has been drastically reduced, though, and faces the threat of additional minimization in the years ahead. Approximately 12 hectares of mangroves were killed by Hurricane Hugo in 1989; human intervention and natural recuperation have had limited success in bringing them back. Mangroves and their ecosystems thrive in protected bays. Unfortunately, these bays are also ideal locations for marinas and boat facilities. Increased activity and any proposed new construction would not only threaten the trees, but the habitat they support as well. Four types of mangrove trees grow in this mangal.
Working together, the red, black, white and grey mangrove trees create an environment where flora and fauna can thrive because they are sheltered… and yet, the trees themselves are imperiled. Although mangroves, with their intricate root systems, are able to withstand wave impacts and winds that would fell many other trees, they are not immune to the ravages of the most severe tropical storms. When Hurricane Hugo decimated Salt River Bay’s mangroves in 1989, old growth was almost completely denuded or destroyed. Ten years later, an effort was made to restore the mangal, as the Virgin Islands Marine Advisory Service and The St. Croix Environmental Association planted 18,000 red mangrove propagules and 3,000 black mangrove seedlings.
According to the National Oceanic and Atmospheric Administration data.noaa.gov), only 31% of the red propagules and less than 1% of the new black mangroves planted survived. Mother Nature can be rough, but the human factor can be the most deadly. Today, unfortunately, the mangroves are challenged by commercial and recreational human activity as well. Some kayakers and sailors use them as starting points for adventure; snorkelers take advantage of the rich abundance of young sea life that swim in the waters they encircle.
Occasionally, they dump their trash in the mangroves, insensitive to the harm this causes the vegetation, birds, fish and other animals living there. More nefarious is the damage that can be caused by large-scale development and resultant pollution, including oil spills from increased boat traffic and runoff from industrial and agricultural sources (including pesticides). As the Virgin Islands were developed, mangroves were cut down, surrounding waters were dredged for docks and marinas, and unspoiled lands were filled in for new construction. It would be nice to think these activities were all in the past, but they’re not. Although all four species of mangrove are protected by the Endangered and Indigenous Species Act of 1990, which forbids pruning, cutting, or removing trees, and although Salt River Bay is a protected National Historic Park & Ecological Preserve, the mangal faces very real danger in the near future.
The National Park Service (NPS), the Office of Insular Affairs (OIS), the Government of the Virgin Islands, and a consortium of four universities (the University of North Carolina Wilmington; the University of the Virgin Islands; Rutgers, the State University of New Jersey; and the University of South Carolina) are planning to build the Salt River Bay Marine Research and Education Center (MREC) on Hemer’s Peninsula, adjacent to Salt River Bay. A quick look at the plans for this facility reveals that its parking lot could be located in an area now occupied by mangroves. With 150,000 square feet of new construction—60,000 sq. ft. of buildings, 40,000 sq. ft. of water tanks and equipment, and 50,000 sq. ft. of roads and walkways—it is impossible to believe that the MREC won’t have a significant and deleterious impact on a delicate and fragile ecosystem. Interested in safeguarding these treasured sentinels?
Troubled citizens have approached the NPS, the OIA, and the consortium with alternatives which could enable them to build their proposed facility at an ecologically (and economically) more responsible site. Environmentally concerned individuals can learn more about their position and join them in taking action by visiting the website www.savesaltriverbay.com. It provides ample information about the situation, and provides the tools for addressing decision-makers, to dissuade them from allowing further development at this location, where the majority of St. Croix’s irreplaceable mangroves are found.
Meet the Salt River Bay Mangrove Family. Closest to the water are the red mangroves (Rhizophora mangle), which stand at the front of the intertwining phalanx of plants. They have thick, jumbled “proproots”— big, curved roots that rise out of the water, trapping run-off and slowing natural currents. Proproots, a favorite scampering place for young crabs, provide an ideal nursery where fish, sea turtles, sponges, mollusks, spiny lobsters and brine shrimp can feed and grow, protected from predators until they’re old enough to thrive in open waters. Dozens of species of juvenile fish have been identified in Salt River Bay’s proproots, including barracudas, groupers, barjacks, doctorfish, and multiple varieties of parrotfish, grunts, and snappers. Both recreational and commercial fishermen, as well as snorkelers, rely on the mangal to keep local waters stocked.
The red mangrove’s proproots absorb the salt water which surrounds them. The trees secrete the salt through tiny pores in their leaves. As they fall into the water, these leaves decay and feed the mold and bacteria around them, joining with the sand, silt and algae to form rich sediment in which newer trees can grow. In doing so, they actually create new land—a staggeringly important function in this day of rising sea levels and rapidly eroding shorelines. Black mangrove trees (Avicennia germinans), which get their name from the color of their trunks and heartwood, cannot grow with their roots continually underwater. They are found just a bit further inland than red mangroves, where they are only submerged during storms and high tides. Rising tall out of oxygen-deprived mud, they have a unique system of roots known as pneumatophores, which look like pencils and work like snorkels, sticking out of the soil and water surface so they can find and absorb oxygen. They trap sediments and solids, thereby reducing shoreline erosion.
These pneumatophores also form an ideal place for birds to hide their nests. Salt River Bay’s mangroves are a habitat where frigate birds, pelicans, herons, egrets, hummingbirds, and many other species have made their homes. Further from the water’s edge is the white mangrove (Laguncularia racemosa), which can grow either as a spreading shrub or a medium-sized tree. It is distinguished by the light color of its tannin-rich bark and the shape of its leathery-textured leaves…rounded, unlike the elliptical leaves of red mangroves or the narrower, hairy, salt- encrusted leaves of the black mangroves.
They may have either proproots or pneumatophores, depending on where they’ve germinated. Salt River Bay is also home to a peripheral species, the grey mangrove (Conocarpus erectus), a small tree or shrub. Its dense, rounded flower heads give it the name by which it is known in the islands: the buttonwood.
Unlike other mangroves, it lacks “vivipary”—its seeds do not germinate before they leave the parent plant. Please help us protect the protectors. Visit www.savesaltriverbay.com— learn more, take action and sign the online petition.