Sentinels of the Sea


  1. Mangroves are ‘sentinels’ of the coasts. Serving as ‘buffers’, they protect the coasts, especially the inland communities, against coastal erosion and storms [1,2].
  2. Tropical and subtropical coasts are their only home. These plants are uniquely equipped to thrive in waters of high salinity, anaerobic soil, unforgiving tides, and strong winds [3].
  3. They can store, exclude, or eliminate salt. Species of Rhizophora and Bruguiera have ultrafilters in their roots, excluding salt. Meanwhile, Avicennia and Acanthus absorb salt, then excrete them via specialized glands in their leaves. The salt-lover Lumnitzera and Excoecaria can store salt in their leaf vacuoles, or transfer them in senescent leaves or bark [3]. They can be really flexible, right?

    Salt crystals excreted from a mangrove leaf (Photo from
  4. Mangrove forests are haven for many terrestrial, estuarine and marine organisms. One can find insects, sea turtles, alligators, snails, crabs, mudskippers, seabirds, juvenile fishes, shrimps, prawns, dolphins, sea otters, and a lot more seeking refuge within this productive ecosystem [3].lemonshark

    Baby lemon shark cruising in mangroves (Photo by Shane Gross).
  5. They are generous, nourishing mothers. Certain species exhibit true viviparity, wherein the propagules are attached to their maternal plant for a year, receiving continuous nourishment [3].

    A red mangrove propagule (Photo from Save Goat Islands)
  6. They protect against sea level rise. A study revealed that over time, as coastal estuaries receive run-off, sandbanks and channels are formed. Essentially, mangroves accumulate more sediments while simultaneously increasing soil elevation, thus dissipating sea level rise [6]. That’s a defender for you!
  7. They are gatekeepers of carbon. That is, they tremendously help battle climate change. Mangroves sequester an astounding 25.5 million tons of carbon yearly [2,9]. Based on a study, no other forests in the world can store carbon as much as mangroves do. “Per hectare mangrove forests store up to four times more carbon than most other tropical forests around the world.” [5]. It’s best being stored, right? Unless we continue protecting these unique ecosystems, we sure are in trouble releasing humongous amount of carbon back to the atmosphere.

    Multiple carbon sequestration in a mangrove ecosystem ( Photo from Blue Carbon – Natural Capital Project)
  8. They are humble space savers. With all the ecosystem endowments we receive, they occupy a mere 0.12% of the world’s total land area [2,8].
  9. They serve as an economic backbone for tropical coastal regions. They return at least $1.6 billion per year in “ecosystem services”, like flood protection, nutrient and organic matter recycling, sediment control, and fisheries” [2,7].
  10. Shrimp/fish culture and other aquaculture are major culprits to dramatic mangrove loss. 38% alone of mangrove loss can be traced to conversion of mangroves to shrimp culture; another 14% from other aquaculture activities [2,10]. In the Philippines alone, half a million ha were decimated to only 120,000 ha, while culture ponds elevated to 232,00 ha [4].
  11. Without them, there would be less fish – and we’ll starve. About 80% of global fish catches are strongly influenced by mangroves [2, 10], since they serve as natural habitats – ‘nurseries’ for an array of marine organisms [3].

    Green nursery
    Mangroves provide a refuge for a school of juvenile fish (Photo from National Geographic by Octavio Aburto).
  12. There are around 70 known species of mangroves. Eleven species are considered at a higher risk of extinction based on IUCN assessment. They may disappear a century from now [2], unless we protect them to the end, just as they do for us.
  13. They survive when they are planted on the right conditions. There have been many attempts to restore mangrove populations, especially because of natural disasters. Most attempts in the Philippines result to minimal mangrove survival, around 10 to 20%. This can be amplified if we plant the right species given the environmental factors. For instance, instead of Rhizophora, natural colonizers Avicennia and Sonneratia must be planted in sandy substrates of exposed coastlines. Also, it is crucial that mangroves be planted in the middle to upper intertidal zone [4].


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[1] Das S., & Vincent, J. R. (2009). Mangroves protected villages and reduce death toll during Indian super cyclone. Proc Nat Acad Sci 106: 7357–7360.

[2] Polidoro, B. A., Carpenter, K. E., Collins, L., Duke, N. C., Ellison, A. M., Ellison, J. C., … & Livingstone, S. R. (2010). The loss of species: mangrove extinction risk and geographic areas of global concern. PLoS ONE 5(4):e10095.

{3] Kathiresan, K., & Bingham, B.L. (2001). Biology of mangroves and mangrove ecosystems. Advances in Marine Biology 4:81-251.

[4] Primavera, J. H., & Esteban, J. M. A. (2008). A review of mangrove rehabilitation in the Philippines: success, failures and future prospects. Wetlands Ecology and Management 6(5):345-358.

[5] Donato, D. C., Kauffman, J. B., Murdiyarso, D., Kurnianto, S., Stidham, M., & Kanninen, M. (2011). Mangroves among the most carbon-rich forests in the tropics. Nature Geoscience 4(5):293-297.

[6] van Maanen, B., Coco, G., & Bryan, K. R. (2015). On the ecogeomorphological feedbacks that control tidal channel network evolution in a sandy mangrove setting. In Proc. R. Soc. A (Vol. 471, No. 2180, p. 20150115). The Royal Society.

[7] Costanza R., d’Arge R., de Groot R., Farber S., Grasso M., Hannon, B.,… & Raskin, R. G.(1997). The value of the world’s ecosystem services and natural capital. Nature 387: 253–260.

[8] Dodd, R. S., & Ong, J. E., & Polunin, N. V. C. (2008) Future of mangrove ecosystems to 2025. In: Polunin NVC, ed. Aquatic ecosystems: Trends and global prospects. Cambridge: Foundation for Environmental Conservation, Cambridge University Press. pp 172–187.

[9] Ong, J. E. (1993). Mangroves – a carbon source and sink. Chemosphere 27(6): 1097–1107.

[10] Ellison, A. M. (2008). Managing mangroves with benthic biodiversity in mind: moving beyond roving banditry. Journal of Sea Research 59(1):2-15.


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