Understanding the full potential of mangroves and their role in climate change
Mangroves are trees and shrubs that grow in tropical and subtropical saline coastal habitats, usually between latitudes 25° N and 25° S. These form woodland or a shrubland habitat, in coastal or estuarine conditions where sedimentation of silts occurs. The habitat itself is referred to as a mangrove swamp, mangrove forest, or simply mangrove. Mangroves have important ecological roles, including providing nursery grounds for many species of fish and crustaceans.
Mangroves are part of the Coastal Lagoon Ecosystem. This compromises of mangroves, seagrass and coral reefs, which all work together to keep our ocean alive and thriving.
There are an estimated number of 73 unique mangrove species in the world, however only four mangrove species are found in the Cayman Islands.
Leaves range in shape and size dependent on the species of mangrove, but ultimately perform the same role - photosynthesis. Although, they widely share similar adaptations: Waxy cuticles - the waxy, coated upper layer of the leaf prevents water loss and extreme exposure to the sunlight. Phototaxis - (meaning movement by light) allows the leaves to turn 'edge on' to the hot sun, reducing burning and water loss through evaporation. Salt Excretion - salt crystals are formed on the leaf's surface as salty water leaves through large stomatal pores, and the water is evaporated.
Nectaries are glands found at the base of White Mangroves which serve as a source of sugar for pollinating insects.
Black Mangrove Leaves
This is a special adaptation of the Black Mangroves, allowing them to survive in brackish conditions.
A protective waxy layer is found on the top of Red Mangrove leaves. Also known as epicuticular wax, this adaptation reduces the rate of transpiration from the leaves - preventing total water loss in the mangrove. This layer also serves as a waterproof wetsuit, helping them to survive in brackish waters, where saltwater can easily flow off the leaf.
Mangrove roots are specifically adapted to a wide range of salinities and low oxygen concentrations in the sediments. They have, for example, specially adapted root-like structures (called pneumatophores) which obtain oxygen directly from the air. The extensive root systems of mangroves help to trap particles suspended in the water and reduce water flow which increases the deposition of sediments. The root systems and accumulated sediments provide habitats for a wide variety of other organisms, including algae, oysters, crabs, barnacles and other crustaceans, sponges and fish.
Desalination is achieved by the blockage of the apoplastic pathway, where water and ions move around the cell membrane and instead travel through the cell walls of root cells. The cell membrane acts as a barrier leaving the salts behind, only uptaking water and needed ions up into the xylem of the mangrove.
Acting as a barrier the root system of mangroves also dissipates wave energy and thus helps to protect coastal areas from erosion.
Substrate anchorage by the roots mitigates erosion of coastal beaches and land due to wave action.
Wave Action on the Coast
This can protect areas that are heavily affected by hurricanes, storm surges, and even tsunamis. With the current rate of accumulation of sediments, some effects of rising sea levels can be naturally countered.
Types of Roots
Although, with current deforestation of mangroves and the increasing rate of which sea levels are rising, sediment deposition might just not be enough to protect our coasts
Red Mangroves - their roots, often referred to as Prop Roots, are long flexible structures that are typically found above ground which transport air to their waterlogged below ground roots. Providing a stable support system, these roots allow red mangroves to grow at towering heights of 80 meters (24 feet).
Black Mangroves - their roots, often referred to as Pneumatophores, are rather shorter, lateral roots with soft spongy tissue. They also have a common name 'Snorkel Roots' as they pierce upward from the ground. Pneumatophores carry out a similar role like that of the red mangroves, aerial roots that help with gaseous exchange - and growing roughly 3 mm per year, they are able to adapt to changing tide levels. However, these roots must be above water for 12 hours a day to allow sufficient oxygen and carbon dioxide intake.
In addition to flexible and durable roots, another feature that can be found on their roots are lenticles. These are cell-sized breathing holes that aid in respiration by allowing gaseous exchange at these aerial sites.
Unfortunately due to climate change, some black mangroves are unable to keep up with increasing water levels and irregular rain patterns, leading to a lack of required gases for respiration and photosynthesis - which may ultimately cause the death of a mangrove.
Examples of Ecosystem Services
Ecosystem Services: These are the outputs and processes from our natural environments and ecosystems that directly or indirectly benefit our quality of life
Mangroves provide many important functions that are key to the Cayman Islands:
- Ideal habitat for animals
- Nursery for fish
- Storm Protection
- Shoreline Protection
- Filters Water
- Tourism and Recreation
- Precipitation Patterns
- Carbon Sequestration
- Builds Land
- Beauty and Inspiration
There are 4 different species of mangroves that harbour in the Cayman Islands -