Moving the MCP mangrove nursery
Harsh habitat and adaptations
Mangrove refers to all halophytic plants, meaning plants that grow in saline soils. They live in a harsh environment – wet saline habitat along tropical coastlines. Living in this habitat means that they have had to adapt to salinity exposure, tidal fluctuations, hot environment and heavy impact from anthropogenic activity that coastlines usually are victims to.
Even though mangroves are most commonly found in saltwater they can also live in freshwater environments. The reason for them mainly living in saltwater environments is due to competition. In the saltwater environment there is much less competition from other plants and so they have adapted to the saline habitat. They have developed different ways to cope with the salinity and a common way is through their leaves. Some species sacrifice a couple of leaves where they send the salt nutrients to, which make the leaves turn yellow and die. Others excrete the salt as the sun evaporates the water, you can recognize those species by feeling or tasting the salt on the leaves. On some species the roots have developed a membrane that prevents salt from entering but allows water to pass through.
Tidal fluctuations mean that mangroves have to cope with the chance of being submerged in salt water at all times. The tidal fluctuations on top of the salinity make it an inhabitable environment for other plants and thus reduce the competition from other plants even further. Root adaptations have made it possible for mangroves to live in soft sediment that is influenced by tides. When walking in a mangrove forest you need to be careful not to fall over roots, because they can extend from both the trunk and branches to increase stability.
These tidal swamp forests are amazing trees, which have found a way to air their roots even when most parts are covered in water – this is their “snorkel” or pneumatophore to ensure that allows the tree to take in oxygen. Mangroves are often exposed to nutrient deficiency in their harsh environment but these incoming tides provide the mangroves with nutrients and remove the excreted waste when the tides go out. Furthermore, propagules or mangrove seedlings, which have adapted to the environment and remain buoyant in water, are transported out with the tides.
Why mangrove nurseries?
You can find mangrove nurseries in many places around the world. This is mainly due to the high anthropogenic pressure that mangroves are victims to. So far, mangroves have adapted to the harsh environment that they are in, but yet they have not had enough time to adapt to rapid increasing anthropogenic pressures. Today they are exposed to dredging, deforestation, water pollution from oil spills and herbicides, and urban development. Destruction of their habitat eventually leads to death of mangrove trees. Due to the pressures that mangroves are exposed to, many places have set up nurseries. The nurseries are important because they increase the chance of propagule survival by 40%
A nursery is typically a place that is suitable for propagules to thrive and grow in without too many factors influencing them. Closed off systems either on land or in water where they are given the right amount of nutrients and not exposed to anthropogenic effects.
Mangroves protect shorelines from hurricanes, storms and erosion. Their root systems stabilize the sediment to prevent erosion. Additionally, mangroves maintain water quality by filtering pollutants and trapping sediment coming from land. Not only do they stabilize sediment and keep the water clean, but these forests act as nurseries for marine life such as shrimps, crustaceans, mollusks and fish. The forest is a rich source of food and offers shelter from predators. In many parts of the world mangroves are also renewable resources used for boats, houses, furniture, medicine or even tea. They are thus not only important for the ecosystem but also have valuable functions that can aid humans. Therefore, mangrove nurseries are important because we want to maintain the mangrove population both for the ecosystem and as a valuable resource.
At Marine Conservation Philippines we had a mangrove nursery ground on base where
mangroves seedlings have been growing for some time. When they had grown big enough we had to replant them in their natural conditions. The time came for them to move out from their nursery and into the real world.
Volunteers brought the seedlings to the nearest estuary where we know that mangroves are thriving. Selecting the site is a process that needs to be thought through. Questions to ask yourself before choosing a location are; how exposed will they be to tidal fluctuations, is there seagrass or other intertidal habitats (because then they should not grow there), how soft is the substrate and how exposed are they to anthropogenic pressures.
Their sizes need to be considered when finding the right spot for each individual. We have to walk in the mudflat to find the best location for the seedlings.
We brought the mangrove propagules out into the water and dug a little hole in the mud where it could fit into and where it would not drown. The volunteers built a little fence around the not yet mature plants it to protect them from dogs and possible human activity. Signs and posters were also created to inform the community about what mangroves are and why we built a fence there. We will continuously keep an eye on the new mangroves to ensure that they are growing as we expect them to. Hopefully, there will be even more mature mangroves to bring out into the “big forest” soon.