At the highest elevation along the estuary, where water is confined by natural features, a mixture of black, red and sometimes white occurs. These trees seem to thrive in standing water and are adversely affected during periods of drought. Buttonwood also occurs on the higher elevations. Because of the nature of the substrate and due to very low light conditions, only special plants can coexist here. Algae, fungi, some halophytic shrubs, and many epiphytes thrive.
Mangroves form dense, almost impenetrable thickets which buffer the physical forces of storms.
They clean water by trapping silt, nutrients, and toxic substances, and they prevent land erosion. More importantly, they play a leading role in providing wildlife habitat, and in the general ecological productivity of the island. The mangrove system is the critical feeding and breeding area for many shore birds, reptiles, and amphibians, and certain mammals. All the mangrove species contribute to the food chain, although their contribution is not always immediately available. The mangrove intertidal zone, with its nearby shallow estuary, is a prime nursery and feeding ground for marine species such as shrimp, mullet, snapper, red drum, and blue crab.