The term 'mangrove', is used in the broad sense either to refer to the highly adapted plants found in tropical intertidal forest communities or the ecosystem itself. The term 'mangrove' may have been derived from a combination of the Malay word 'manggi-manggi', for a type of mangrove tree (Avicennia) and the Arabic 'el gurm', for the same, as 'mang-gurm'. As a word, it can be used to refer to a species, plant, forest or community!
Structure of Mangrove Forests
3 horizontal zones with trees about 15m tall.
- Coastal zones
- Nearest to the sea, flooded with saltwater and high tides.
- Trees have tube-like breathing roots.
- Eg: Avicennia species (pencil shaped)
- Middle zone
- Trees have prop or stilt roots growing from trunks for anchoring plants firm to muddy soil.
- Eg: Rhizophora species
- In-land zone
- Trees have knee - like roots to provide support on soft soil.
- Eg:Bruguiera species that are least salt - tolerant
Niche
Refuge: Tree climbing crabs and sea snails climb up their aerial roots at high tide to avoid aquatic predators. Their branches provide shelter for creatures from Proboscis Monkeys and nesting sites for large herons and to crevices of insects.
Food: Monkeys consume the shoots and leaves, small insects nibble on them. Fallen leaves are important nutrients for both within the mangrove habitat and when it is flushed out to the coral reefs. Leaves are broken up by crabs and other small creatures, and further broken down by microorganisms to produce minerals. There are tiny moth larvae that feed on air roots (pneumatophores).
Natural water filter: A huge number of filter-feeders are fastened on the tangle of roots. Example like, barnacles and shellfish. These filter feeders clean the water of nutrients and silt. As a result, clear water washes out into the sea, allowing the coral reef ecosystem to flourish.
Stabilise the coast and river banks: Their roots prevents mud and sand from being washed away with the tide and currents. Mangrove trees also slowly regenerate the soil by penetrating and aerating. Creatures such as crabs and mud lobsters also help in. As the mud builds up and soil conditions improve, other plants can take root. Mangrove trees also reduce the damages caused by storms.
- Plant survive in this environment, it must tolerate broad ranges of salinity, temperature, and moisture, as well as a number of other key environmental factor because……
- When high tide brings in salt water, and when the tide recedes, solar evaporation of the seawater in the soil leads to further increases in salinity. The return of tide can flush out these soils, bringing them back to salinity levels comparable to that of seawater.
- At low tide, organisms are also exposed to increases in temperature and desiccation, and are then cooled and flooded by the tide.
Hence… ADAPTATION OF PLANTS!!!!
Adaptations
Adaptation to low oxygen:
- They prop themselves above the water level with stilt roots to absorb air through their barks (lenticels) and aerial roots that is exposed to air.
Limiting to salt intake:
- Mangroves exclude salt by having significantly impermeable roots which are highly suberised, acting as an ultrafiltration mechanism to exclude sodium salts from the rest of the plant. Analysis of water inside mangroves has shown 90% to 97% of salt has been excluded at the roots.
Limiting water loss:
- Because of the limited fresh water available in salty intertidal soils, mangroves limit the amount of water they lose through their leaves. They can restrict the opening of their stomata (pores on the leaf surfaces, which exchange carbon dioxide gas and water vapour during photosynthesis). They also vary the orientation of their leaves to avoid the harsh midday sun and so reduce evaporation from the leaves.
Nutrient uptake:
Because the soil is perpetually waterlogged, little free oxygen is available. Anaerobic bacteria liberate nitrogen gas, soluble iron, inorganic phosphates, sulfides, and methane, which make the soil much less nutritious.Pneumatophores (aerial roots) allow mangroves to absorb gases directly from the atmosphere, and other nutrients such as iron, from the inhospitable soil. Mangroves store gases directly inside the roots, processing them even when the roots are submerged during high tide.
Different types of aerial roots:
1. Stilt roots - Stilt roots also called prop roots are developed by Rhizophora species and Pandanus species.
- 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.
- to allow the exchange of gas in oxygen-poor sediments.
- Provide habitat and protection for organisms.
2. Knee roots
- Allow the exchange of gases in oxygen-poor sediments.
- provide support in the muddy area
3. Pneumatophores
Enable gas exchange directly above the surface and provide the additional needed oxygen which can't be taken from the soil.
*All aerial roots also contain large air spaces (aerenchyma). These not only transport air, but also provide a reservoir of air during high tide when all the aerial roots may be underwater.
*All mangrove trees exclude some salt at the root level, some have effective ultrafiltration at the root level to exclude more salt. Any salt that gets through are believed to be stored in old leaves which are later shed.
Case study Indonesia, Sumatra:
During natural disaster, for example the tsunami that happened in Indonesia 7 years back in 2004 when a magnitude 9.1 earthquake struck Indonesia, Sumatra, the mangrove actually helped to reduce that impact of the deadly tsunami! The mangrove forest and and coastal vegetation creates a shore protection in that area. With the strong hold of aerial,prop and knee roots, which created a “barrier”and eventually slows down the speed of the tsunami! This amazing mangrove not only reduced the amount of death tolls but also reduced the damage that it would have cause.
Species that can be found:
Scylla serrata
Africa, Australia and Asia. In their most common form, the shell colour varies from a deep, mottled green to very dark brown.
Mudskipper
Mudskippers are unusual fish that like to live in mangrove habitats, because they spend a lot of their time out of the water. They can breathe by holding water in their mouths and gills, and by staying damp they can also breathe through their skin.
References:
http://www.botgard.ucla.edu/html/botanytextbooks/worldvegetation/marinewetlands/mangal/generalcharacteristics.html
