About Mangrove

Mangrove Swamp

 

What is a mangrove swamp?

It is a tidal swamp which is dominated by mangroves.(a tree or shrub which grows in tidal, chiefly tropical, coastal swamps, having numerous tangled roots that grow above ground and form dense thickets.)

 

Structure of the mangrove swamp

The mangrove swamp consist of three distinct zones: the Coastal zones, Middle zone and the Inland zone. Different unique species of plants could be found in this three different zones.

Adaptation

Roots

Mangroves have three basic organs like any other ordinary plant, the stem, the leaf and the root.  The root system of mangroves is divided as in other plants in three main groups: flat root system, heart root system and top root system.


   





The flat root system's primary root is hardly or not at all developed, therefore the lateral roots are strongly developed. Flat root systems are found especially in solid, dense and impermeable soils. Concerning mangroves especially Avicennia species develop flat root systems and therefore have an advantage compared to other mangrove species as they can easily establish in sandy, stony and rocky coastlines.

       
The heart root systems develops many, differently strong main roots simultaneously which grow vertically into the ground. Especially mangroves like Avicennia, Ceriops, Rhizophora and Sonneratia species as well as Nypa fruticans and Pelliciera rhizophorae, mangroves that often grow directly in the tides and need to protect their location, depend on the successful heart root system which develops roots like anchors in all directions. This characteristic increases the chances for these mangrove species to survive and grow in different areas like muddy, sandy, rocky or coral-like soils and coasts.

The tap root system develops one single, strong and dominant main root that grows vertically into the ground. This main root has the ability to reach groundwater. This ability is not really necessary for mangroves growing in the tides but for mangroves growing a little bit more inland like Barringtonia asiatica for example. Dry and well drained soil is a typical feature of plants developing tap root systems.

Compared to other plants mangroves differ visually especially by their famous and typical aerial roots and biologically through the ability to grow in saline areas.

Aerial roots are roots with various abilities and functions, primary gas exchange in oxygen-poor soils. The aerial roots are divided into groups as follows:

• Stilt roots     
• knee roots
• Pencil roots
• Cone roots
• Butterus roots 
• Spreading roots
• No-Aerial roots

Stilt roots(Coastal zone)

Stilt roots also called prop roots are developed by Rhizophora species.

Stilt roots outgrow the trunk of the mangrove, branches or already existing stilt roots.

As soon as stilt roots reach the ground the tip of the stilt root develops an underground root system with which it connects the stilt root into the ground and then develops one or more further stilt roots which grow arcuately into the air to again run into the ground to develop an underground root system, this process repeats several times.

  

If the stilt root hits water instead of soil the stilt root will grow underwater toward the soil in the ocean or any other subject, a reef or some corals for example, that the stilt root can hold on to and be rooted to. Once the tip of the stilt root meets a subject it can root to many smaller roots develop to anchor themselves to the subject or in the soil.

Stilt roots have numerous functions one of the most important one of the most important one is to uphold the mangrove and ensure its growing space. The tides are rough, huge waves, strong winds, tropical storms such as typhoons and hurricanes do not make it easy for mangroves.

Thus to ensure living in the tides it is important for Rhizophora mangle to develop numerous massive stilt roots.

Another important ability of stilt roots is to allow the exchange of gas in oxygen-poor sediments.

The arc-shaped prop roots often can be found with a huge amount of lenticels that allow gas exchange in the oxygen-poor soils. Hence the popular term aerial roots. Stilt roots growing in soils with sufficient oxygen often only have a supportive function and do not develop so many lenticels.            

As humans we often see the stilt roots above the water surface, the entangled root system of stilt roots under water can be huge and very impressive, it provides useful services to its environment. Countless animals, especially fish, seahorses, shells and crustaceans find shelter in the root system of mangrove stilt roots, they provide protection from predators and a perfect nursery.

 Stilt roots bind sediments and ensure sustainable coastal protection by sediment accumulation and counteract coastal erosion.

Knee roots(Middle zone)

Knee roots are developed by Bruguiera species.

Knee roots emerge as a root loop from the underground root system and allow the exchange of gases in oxygen-poor sediments. Each underground horizontally growing root develops several knee roots at regular intervals.
Knee roots of an adult Bruguiera gymnorhiza for example extend in a radius of approximately 10 meters around the trunk and can reach a height of up to 60cm.

The knee roots of the different Bruguiera species differ in size, shape and frequency and can vary depending on the location and growth conditions.

Most knee roots have numerous lenticels with the ability to exchange gas.

Cone roots(Inland zone)

Sonneratia species grow in oxygen-poor sediments. The underground root system needs and demands oxygen, the soil is not able to support the underground root system with enough oxygen, therefore the underground root system outgrows aerial roots that grow vertically up to the air above the soil. The cone roots have numerous lenticels that enable gas exchange directly above the surface. The cone roots provide the additional needed oxygen which can't be taken from the soil.            
During high tide the surface tension of the water prevents the inflow of water into lenticels, therefore no gas exchange is possible while the pneumatophores are under water. Permanent inundation of pneumatophores lead to the death of the root system and therefore the mangrove.

        



More Information About Roots

Leaf

Many mangrove species, such as the Grey Mangrove and the River Mangrove (common species along the Redlands coast), have leaves with glands that excrete salt.

Some species such as the Grey Mangrove can also tolerate the storage of large amounts of salt in their leaves – which are discarded when the salt load is too high.

Mangroves can also restrict the opening of their stomata (these are small pores through which carbon dioxide and water vapour are exchanged during photosynthesis). This allows the mangrove to conserve its fresh water, an ability vital to its survival in a saline environment.

Mangroves are able to turn their leaves to reduce the surface area of the leaf exposed to the hot sun. This enables them to reduce water loss through evaporation.

Reproductive Adaptation

Some mangrove species have evolved to produce seeds that float. The tide acts as the method of dispersal to avoid crowding of young plants.