Although the propagule varies in size among species of Rhizophora , all float in sea water for a time following detachment from the parent plant. Eventually the propagule will become vertically erect in the water and become rooted in a quiescent environment, as shown here near Fort Pierce, Florida. Adaptation to Salinity and Salt Excretion Photo by Robert Twilley Mangroves are halophytes, or salt-tolerant plants. They can tolerate more salt in their sap than terrestrial plants, although there is variation among mangrove species in the degree of tolerance. The most tolerant species have salt glands in their leaves, allowing for the secretion of salt, as shown here on the leaf of Avicennia germinans in southwest Florida during the dry season when soil salinity is greatest.
Fine sediment accumulates around mangals, making for very turbid water at high tide.
The mud flats that accumulate are rich in particulate organic matter and benthic animals. In many coastal areas mangrove islands are distributed throughout shallow bays and lagoons and are frequently used as bird rookeries because they provide protection and isolation from predators. The birds deposit guano that helps provide nutrients for the trees. Mangrove Hammocks Photo by Robert Twilley Mangrove islands also occur along inland coastal areas of land as shown here in the Everglades National Park in south Florida. These mangrove islands are known as hammocks and form tear shape patterns parallel to the flow of water and to the coast.