There are many ecosystems on land, and many others marine. And where the sea and the land meet, others are formed, very different from the rest, which obey the cycles of the tides. In the coastal regions there is also a wide diversity of ecosystems, but few are as spectacular as the mangroves, typical of tropical and subtropical latitudes, which can be found in Africa, Asia, Oceania and, above all, in America.
Mangroves are ecosystems with great biological diversity , very rich and very productive. They are also a refuge for a large number of animals, especially molluscs, crustaceans, fish and birds. Its structure resembles that of a flooded forest and, therefore, dominated by one or more species of trees.
The tree that dominates the mangrove ecosystem receives the common name of mangrove . There are more than 50 different mangrove species, belonging to 16 different botanical families.
An ecosystem of two environments
One characteristic that makes the mangrove such a peculiar ecosystem is that it extends from the bottom, through the entire water column to the surface, and several meters above it. The mangrove canopies spread like a green mantle several meters thick on the surface of the water. From the branches, when they touch the surface, adventitious roots sprout that go into the water, until they bury themselves in the bottom, taking root in the substrate.
The final result is a dense and populated tree canopy , formed by a complex network of branches, which is supported by long roots, as if they were stilts. In the emerged part, the epiphytic plants —plants that grow on other plants— enrich the plant biodiversity of the ecosystem and form, where the network is denser, small portions of soil where herbaceous plants or ferns take root. In addition, the tree canopy provides shelter for birds and insects.
Beneath the surface, however, lies a very different world. The roots, like columns, interrupt currents and prevent bottom erosion , creating areas of calm water where multitudes of fauna can enter and take refuge. Sometimes the density of the roots is so high that larger fish cannot enter the dark tranquility of the heart of the mangrove, and it serves as a hiding place for their prey.
A bridge between two worlds
The particular shape of a mangrove makes it a unique type of ecosystem. Ecosystems, in general, and especially the more mature ones, usually have complex and highly developed cycles of matter and energy within them, but the exchange of energy with neighboring ecosystems is relatively low . For this reason, the flow of matter and energy between terrestrial and aquatic ecosystems is relatively low. But the mangroves break this trend.
The mangrove behaves like a forest in its emerged part, which produces large amounts of biomass . But, this biomass, which in a normal forest would end up accumulated in the soil transporting very little to the outside, especially by runoff, in a mangrove it precipitates in the water . Thanks to coastal currents, some of this organic matter can travel miles and be deposited in far away places. Sea urchins have been found at the bottom of a Caribbean ocean trench with remains of mangrove leaves in its stomach.
But not all that matter has to be lost in the ocean. When the sea is calm, or when the network of roots is so dense that it prevents the currents from dragging much of the biomass, the mangrove facilitates the sedimentation process , which can lead to the formation of new islands.
Ultimately, the mangrove can become a protector of inland terrestrial ecosystems . The density of the canopy greatly reduces the force with which waves or floods rush against the shoreline. Even the damage caused by storms or tidal waves is partially buffered by the presence of mangroves. In addition, they are a powerful sink and store of atmospheric carbon, which helps mitigate the effects of climate change; however, it is an ecosystem sensitive to changes in climate. For all these reasons, mangroves are considered priority ecosystems to conserve.
References:
Alongi, D. M. 2008. Mangrove forests: Resilience, protection from tsunamis, and responses to global climate change. Estuarine, Coastal and Shelf Science, 76(1), 1-13. DOI: 10.1016/j.ecss.2007.08.024
Field, C. et al. 1998. Mangrove biodiversity and ecosystem function. Global Ecology & Biogeography Letters, 7(1), 3-14. DOI: 10.1111/j.1466-8238.1998.00278.x
Ramos, J. a. A. et al. 2011. Influence of moon phase on fish assemblages in estuarine mangrove tidal creeks. Journal of Fish Biology, 78(1), 344-354. DOI: 10.1111/j.1095-8649.2010.02851.x
Rodriguez, C. et al. 1990. The epiphyte community of mangrove roots in a tropical estuary: Distribution and biomass. Aquatic Botany, 36(2), 117-126. DOI: 10.1016/0304-3770(90)90076-W
Vannucci, M. 2001. What is so special about mangroves? Brazilian Journal of Biology, 61(4), 599-603. DOI: 10.1590/S1519-69842001000400008
