Mangrove ecosystems have a very narrow band of distribution and are found in tropical and subtropical areas around the world. They are amongst the most rare and interesting ecosystems that occur in the tidal or coastal environment. Mangroves consist of unusual salt-adapted trees which allows them to thrive in the intertidal zone, a habitat that is normally too salty for trees. Some mangrove trees even live below the low tide line where their roots are constantly in the water. Mangrove trees have developed adaptations to allow them to cope in this otherwise harsh environment where some species have roots that can filter out the salt from the water while others have leaves which are able to secrete excess salt. Many mangrove species have prop roots which form higher up on the tree’s trunk and as a result have sections exposed to the air while the rest of the root extends through the water and into the sediment layer beneath. Other species have knee roots, which grow beneath the sediment and produce branches which point up into the air, these branches have pores at their tips which air enters and oxygenates the rest of the underwater root.
Mangroves have a number of important ecosystem functions. During storms their roots hold the bottom soil in place while their branches reduce the force of the waves hitting the coastline. Mangroves also provide shelter and food to a number of different species which live in the mangrove swamps including a variety of birds, fish, crabs, and shrimps. Mangrove swamps are also used by various fish species as mating grounds and nurseries. In addition, mangrove swamps can be used as a type of filter against the introduction of pests and exotic insects.
There is a lot of concern regarding the effects of climate change induced sea level rise on mangrove swamps. With rising sea levels mangrove swamps will be flooded which will change the salinity of the water, and the plants will be starved of the sediment layer in which they grow. They will be unable to adapt fast enough to move to higher land, especially if constrained by urban environments.
Written by: Minke Witteveen
For further reading:
- Armstrong, M. 2001. (Ed) Aquatic Life of the World. Marshall Cavendish Corporation: New York. Pp324-325.
- Smith, J.B., Schellnhuber, H-J. & Mirza, M.M.Q. 2001. Chapter 19: Vulnerability to Climate Change and Reasons for Concern. In: Impacts, Adaptation, and Vulnerability. McCarthy, J.J., Canziani, O.F., Leary, N.A., Dokken, D.J. & White, K.S. (Eds) 934.