Defining Mangrove Habitats
Mangroves are unique ecosystems found near tropical and subtropical bodies of water throughout the world. These habitats usually exist in slow-moving coastal waters, although they can also occur along river banks and in estuaries. In these locations, rivers flow into the ocean, leaving behind large deposits of mud and fine silt. Additionally, the water in these areas is a mixture of freshwater and saltwater, creating a unique environment. Mangroves are characterized by the presence of large trees, which are also referred to as mangroves, that have large systems of exposed roots that are often said to look like stilts. Globally, mangrove habitats cover a total area of around 52,300 square miles, and exist on every continent that has subtropical and tropical climate zones. In addition to mangrove trees, mangrove habitats are also home to a number of other plant species. The remainder of this article highlights the special features that allow mangrove plants to survive in such a unique habitat.
Categories of Plants Found in Mangrove Habitats
The principal plants found in mangrove habitats are mangrove trees and shrubs. Generally speaking, researchers divide mangrove plants into two categories: true mangroves and associate mangroves. True mangrove plants are those that are endemic to mangrove habitats, meaning they cannot grow and do not exist outside of the high saline, low oxygen conditions of mangrove habitats. Associate mangrove plants are those that can exist in a variety of ecosystems, including inland habitats, mangrove habitats, and high saline habitats. Associate mangrove plants typically grow along the outer edges of mangrove habitats.
True Mangrove Plants
Researchers have identified 69 true mangrove plant species, which are further categorized into 20 different plant families. However, some researchers believe there are as many as 73 true mangrove plant species if hybrid species are included. Examples of true mangrove plants are listed below.
Large-leafed mangroves, also known as oriental mangroves, are one of the most common true mangrove plant species. This tree can grow as high as 114 feet, although its height is much shorter in some regions. It is characterized by dark, thick-skinned leaves that measure between 3 and 8.66 inches in length, and between 2 and 3 inches in width. The oriental mangrove also grows a reddish orange-colored flower. This species is particularly important in the Maldives, where the seedlings provide an important source of food for the local population.
Kandelia obovata exists in some Asian countries, like Japan, Vietnam, Taiwan, and southern regions of China. This tree is characterized by its white, 5-pointed flowers, which bloom between May and July. It reaches 9.84 feet in height and is found growing in downstream estuary zones. Although this species has a conservation status of "least concern," its population is reportedly declining. This decline is due, in part, to the 29% loss of mangrove habitat throughout its native region.
The mangrove apple tree, also known as the crabapple mangrove tree or cork tree, is another true mangrove plant species that can be found in several countries around the world, including Indonesia, Northeast Australia, and tropical areas of Africa. It grows to a height of around 65.6 feet and is characterized by its unique fruit, which looks like a miniature apple. This fruit is an important part of the diet of several communities and can be eaten fresh or prepared as a juice. The roots of this tree are also utilized by local people to create floats for fishing nets. The mangrove apple tree has been categorized in the conservation category of "least concern" by the International Union for Conservation of Nature (IUCN) guidelines.
Features of True Mangrove Plants
Despite the variety of mangrove plant classifications, true mangrove plants share some of the same features that allow them to survive and thrive in mangrove habitats. For example, mangrove trees and shrubs have adapted to oxygen-deficient soil. Although sediment deposits are typically low in nutrients, true mangrove plants have developed the ability to extract sufficient nutrients. Additionally, mangrove trees are able to survive in the unique high saline concentration of mangrove waters, even with constantly changing water levels. Some of the specific features of mangrove plants are explained below.
Perhaps the most important feature of true mangrove plants are their root systems. Whereas most plants obtain oxygen from below the ground, mangrove roots have developed the ability to breathe above ground, thereby obtaining oxygen from the surrounding air. This adaptation explains why mangrove roots have a stilt-like appearance. Obtaining oxygen from the surrounding air is necessary for mangrove plant survival because of the anaerobic conditions found in the soil of mangrove ecosystems.
Another important feature of true mangrove plants is its reproductive behavior. The same conditions to which mangrove trees and shrubs have adapted (low levels of oxygen and nutrients) make seed germination nearly impossible. The reproduction method utilized by true mangrove plants is known as vivipary, which involves a unique form of seed germination in which the seed begins to develop while still attached to the mature plant. While the seed develops, the mature tree to which it is attached provides it with the nutrients and water that it needs for survival. Once the seedlings mature, they drop from the parent plant and float on the water below. The seedlings are able to survive in the water until they attach to soil and take root.
Importance of Mangrove Habitats
Mangrove habitats are of significant environmental and economic importance. One of the most important roles of mangrove habitats is their ability to prevent erosion of coastal areas. The complex root systems of these forests protect shorelines from being eroded over time by waves. Additionally, they collect sediment as it flows downstream and into the ocean. This action helps protect coral reefs and other underwater ecosystems from being covered and destroyed by sedimentary deposits. Mangrove habitats also provide protection to different fish and marine animal species, making them important in sustaining environmental biodiversity and as fisheries for human use.