The word mangrove is used to describe a group of species of trees or shrubs that have adaptations that allow them to colonize flooded lands that are subject to saltwater intrusion. The term includes several species that have similar adaptations but that belong to different families.
Rhizophora mangle (red mangrove)
It is the species of most distribution and until 1918 it was considered the only species in America. The red mangrove is usually, but not exclusively, the species that is found on the outside of stretches of mangrove swamps and on the sides of canals. The most striking characteristic of this species is its system of aerial roots. These roots come from the same trunk or from lateral branches and fall to the ground. The root network provides support to the tree in addition to serving vital functions of nutrition and aeration.
Generally, Rhizophora mangle trees are 4 to 10 meters (13 to 33 feet) high. The leaves are simple, opposing, and petiole, usually 8 to 10 cm (3 to 4 inches) long and 4 to 5 cm (1.5 to 2 inches) wide. The flowers are small, 2.5 cm (1 inch) in diameter with four lanceolate sepals, thick and coriaceous. The flower has four yellowish white petals. It has 2 to 4 flowers per stalk or peduncle.
In Puerto Rico, the common names for the Rhizophora mangle are mangrove, red mangrove, mangle Colorado, mangle zapatero and mangle de chifle.
Laguncularia racemosa (white mangrove)
Laguncularia is a monotypic genus that only includes the Laguncularia racemosa. The white mangrove trees reach up to 20 meters (65 feet) high although generally they reach a height of 4 to 6 meters (13 to 20 feet). The trunk has fissured bark, characteristic that distinguishes it from the black mangrove, which has a one-piece bark.
The leaves are opposing, simple, whole, of coriaceous and succulent texture, oblong with a rounded apex. The flowers are small and numerous, the petals are whitish-gray, tubular, and have five prominent ribs.
The fruit is 1.5 to 2.0 cm long, somewhat flat and finely tomentose. In this species, the fruit detaches easily from the plant. It can germinate quickly once it falls, or it can float for 20 to 30 years.
Laguncularia racemosa has a shallow root system with roots that come from the trunk in a radial manner and produce geotropically-negative projections (pneumatophores) that protrude from the ground. These pneumatophores are not as developed and usually occur as aggregates near the trunk. The pneumatophores exit the root as a whole but then bifurcate near the surface.
Conocarpus erectus (Button Mangrove)
Conocarpus genus consists of two species, but only Conocorpus erectus is part of the mangrove association.
This species is not generally considered a true mangrove but rather a peripheral species. It is produced in the highest areas and over less salty, sandy terrain. Often it develops as a bush, but in favorable places it develops as a tree reaching 5 to 7 meters (16 to 23 feet) high. Conocarpus erectus is the only species of mangrove with alternating leaves. The leaves are 4 to 9 cm (1 1/5 to 3½ inches) long and 2 to 3.5 cm wide, elliptical or elliptic-lanceolate with two glands at the base. The petioles are short.
The flowers are tiny (2 mm wide), green and fragrant, gathered in globular inflorescence 6 to 12.5 mm in diameter. The globules become an aggregate and round fruit, hairy and chestnut-brown. Each globule contains many seeds.
In Puerto Rico Conocarpus erectus can form monospecific forests in lagoons of low salinity (5) that have been isolated from the coast. It often forms groves over rocky coasts. The common names in Puerto Rico for Conocarpus erectus are button mangrove and buttonwood.
Avicennia germinans (black mangrove)
Avicennia germinans genus is distinguished by the protruding development of pneumatophores. These organs originate from root systems that are very superficial and set out radially around the trunk. Pneumatophores stem from these radial roots and reach heights of 20 cm (8 inches) or more above the ground. Like Laguncularia, the role of pneumatophores is to ventilate the root system.
Avicennia germinans trees are of variable size and reach up to 15 meters (49 feet) in height and a diameter of 30 to 50 cm (12 to 20 inches) or more. However, in highly salted areas or in marginal and harsh environments, they grow as short shrubs. The species has an outer crust, black or dark gray, with a yellow interior.
The leaves are opposing, elliptic-lanceolate, with a smooth edge and a sharp apex. Generally, they reach 8 cm (3 in) long and 3 cm (1 in) wide. The flowers are sessile; they are arranged in groups and are small, 5 mm in length and 2.5 mm in diameter. The fruit is an oval and flattened capsule; the embryo develops before the fruit falls off.
Avicennia germinans is the species most tolerant to harsh climatic and soil conditions. For this reason, it is often the predominant or exclusive species in marginal environments on latitudinal boundaries or in areas where soils contain high concentrations of salt. The common names in Puerto Rico for Avecennia germinans are salty mangrove, black mangrove, or silly mangrove.
Mangroves are important ecosystems and have different roles which are at the service of human beings, for free. They serve as habitat for a variety of species of fish, birds, and mammals associated to these systems and have additional values needed to sustain environmental quality.
These resources regulate the flow of rainwater, reduce the impact of floods and control soil erosion; they are buffer zones against contaminants in the water and maintain biodiversity. The economic importance of mangrove swamps in commercial fishing as well as recreational and educational uses should also be emphasized. Many of our fish species that have great commercial value spend part of their life cycle in mangrove swamps.
Despite ecological and recreational importance, human activities have caused the deterioration and loss of these natural resources. Among the causes associated to these activities are over drainage, changes in the natural course of water (canals), cutting of trees in water catchment areas, erosion and sedimentation due to bad soil conservation practices, filling and construction, and the establishment of sanitary landfills or trash dumps, among others.
Historically, these lands have relatively low economic value because of their hydrological condition. Today, many places on our island that are being developed are on lands that were once mangrove swamps because their capital cost of acquisition is relatively low and also, in many cases, they are in tourist attraction areas.
Mangroves have high ecological and economic value. They sustain a substantial number of vulnerable or endangered species. However, the economic development that occurs on our shores is not compatible with the conservation of this important natural resource. If they are lost, their inherent functions which represent a great value for everyone will be lost. Some of these are:
• They are part of the process which supplies moisture to the atmosphere and in doing so becomes a source of natural cooling for communities near them. (evapotranspiration).
• They produce large amounts of oxygen.
• They are a source of organic and inorganic matter that sustains the marine and estuarine food network.
• They sustain a substantial number of vulnerable or endangered species. They are an important nesting place for a number of resident and migratory species. They serve as habitat for marine and estuarine species of high commercial value.
• They stabilize coastal lands from erosion and protect the coast from hurricane winds and other weather phenomena of great impact.
• They are one of the island’s great attractions for both tourists and scientists.
Puerto Rico’s Coastal Zone Management Program
• Compendio Enciclopédico de los Recursos Naturales de Puerto Rico. Volumen II. Ecología del Manglar. DRN. 1988.
Adaptation: Nancy M. Vázquez Guilbert//Collaboration: José R. Casas/Víctor M. Suárez/Iraida García//Pictures: Dra. Alida Ortiz/Dra. Clara Mojica (qed)/Nelly González
• Humedales de Puerto Rico. Vol. 2 Num. 1. Los Humedales: un recurso natural valioso en Puerto Rico. DRNA. 1995.
Sponsored by Puerto Rico`s Coastal Zone Management Program, under the National Oceanic and Atmospheric Administration of the United States.
Author: Grupo Editorial EPRL
Published: August 27, 2014.
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