*This post is by Nina Adamo, a student in Marc's 'Causes and COnsequences of Diversity' class.
Mangroves are among the most biologically important forest ecosystems on Earth, found in the intertidal zone between land and sea along tropical and subtropical coasts around the world.7 Mangrove ecosystems provide habitat for a wide range of terrestrial as well as aquatic organisms including plants, fish, mollusks, birds, reptiles, and crustaceans, among many others.1
Mangroves also serve as nursery habitats for various fish and crab species found in coastal regions, as mangroves provide high abundances of food and shelter for developing wildlife living in coastal regions.7 Since many species use mangroves as nursery grounds, fish diversity and abundance in neighbouring coastal ecosystems has been positively linked to the proximity of mangrove areas, suggesting that mangrove habitat is critical in supporting biodiversity in surrounding coastal ecosystems.5
Figure 1: Many species such as fish and crustaceans use mangroves as a nursery site for their young, where shelter from predators and food is abundant.9
Along with supporting a wide range of biodiversity along coastal ecosystems, mangroves also provide many essential ecosystem services to humans. Some of these societal benefits include natural resources such as fish and timber, coastal protection from storms, and assisting in mitigating climate change by removing carbon dioxide from the atmosphere and storing it.11
Despite the critical role mangroves play in supporting coastal biodiversity and providing ecosystem services to society, mangroves have been disappearing globally at an alarming rate of 1-2% per year due to anthropogenic activities and accelerated global climate change.4 The main threats to these ecosystems are rising sea levels causing coastal erosion, environmental condition changes due to climate change, land-use changes, deforestation, and overexploitation of natural resources.4 This has led to the loss of about 50% of mangrove coverage across the globe since 1950.10
In recent years, there have been a great number of studies that have explored the impacts of anthropogenic activities and climate change on the biodiversity of vegetation, benthic meiofauna, and benthic fauna found in mangrove ecosystems.
Figure 2: A stilt mangrove tree in a mangrove forest coastal ecosystem on an island in East Kalimantan, Indonesia.8
In the Sundarbans, which is the world’s largest remaining natural mangrove ecosystem located on the border of Bangladesh and India, there has been a homogenization of tree species composition over the span of 28 years from the 1980s to the 2010s.10 In other words, the largest remaining mangrove ecosystem has experienced a loss in community biodiversity of mangrove plant species over time due to anthropogenic activities and the environmental impact of climate change.
The loss of biodiversity in ecosystems is a crucial issue because higher biodiversity in most ecosystems typically leads to higher ecosystem functioning, so if biodiversity is lost through stressors such as habitat loss or extreme environmental conditions such as those produced through global climate change, it could have severe impacts on the diversity of an ecosystem and hence the functioning of the ecosystem as a whole.2
The biodiversity of benthic meiofauna, which are very small invertebrates that live in the bottom of aquatic mangrove ecosystems, are also negatively impacted by anthropogenic disturbances. In a comparison study of disturbed and undisturbed mangrove areas, disturbed areas displayed a 20% loss of benthic meiofauna biodiversity compared to undisturbed mangrove areas.2 Since many juvenile fish species that use mangrove ecosystems as nursery grounds rely heavily on meiofauna for food, this loss of biodiversity through anthropogenic causes could cause a reduction in ecosystem functioning not only within mangrove communities but in surrounding coastal ecosystems as well.2
A similar observation is also found with the biodiversity of benthic fauna in mangrove ecosystems in the Philippines, where protected mangrove ecosystems have significantly higher diversity and abundance of crab species than reforested mangrove ecosystems that have been disturbed by humans.1 This suggests that environmental factors influenced by climate change and human influences in mangrove ecosystems can have a negative impact on the biodiversity of benthic fauna, one of the most dominant groups in these systems, which could impair the overall functioning of the ecosystem.1
With the increasing loss of mangrove habitat and the biodiversity within it across the globe due to anthropogenic activities and climate change, it is essential that humans intervene with utilizing other paradigms such as the flagship species paradigm to increase mangrove conservation and policies to protect mangrove habitat,11 well-researched and well-managed mangrove planting restoration,6 and more research on innovative manmade artificial mangroves that may help to restore these ecosystems.3
Figure 3: Locations of the various megafauna found in mangroves (locations of mangrove areas shown in green) around the globe, with the orange representing terrestrial and the blue representing aquatic megafauna. Some examples of megafauna found in mangroves (from top-left to bottom-left in a clockwise direction) include the Key deer, Manatee, Sailfin lizard, Sawfish, Three-toed sloth, Spotted deer, Bengal tiger, Otter, Green turtle, Crocodile, and the Proboscis monkey.11
The focus of much of the recent research on mangrove conservation has utilized an ecosystem services approach, where the benefits that mangroves provide to humans is stressed as an incentive for conservation.11 For this reason, most of the research has been focused on smaller benthic invertebrates such as crabs and shrimp, rather than larger charismatic megafauna that are found in mangroves around the world such as sloths, Bengal tigers, green turtles, and proboscis monkeys.11
Conservation awareness of mangrove ecosystems could be improved by using the flagship species paradigm which uses larger charismatic species found in mangrove ecosystems in marketing campaigns that would protect the entire ecosystem in which they are found. Since charismatic megafauna have been observed in mangrove habitats across the globe, using the flagship species paradigm in conjunction with the ecosystem services paradigm could increase public awareness of the threats facing these extremely diverse and productive ecosystems.11
Conserving mangrove ecosystems around the world is important as these ecosystems provide ecosystem services to human society and play a critical role in supporting biodiversity within mangrove systems and in neighbouring coastal systems. With the increasing threat of anthropogenic activities and global climate change, the conservation and protection of mangroves is essential to reduce the decline in ecosystem functioning and biodiversity in these ecologically important ecosystems that many animals and humans alike rely on in order to live productive and successful lives.
References
1. Bandibas, M. B., & Hilomen, V. V. (2016). Crab biodiversity under different management schemes of mangrove ecosystems. Global Journal of Environmental Science and Management, 2(1), 19–30. https://doi.org/10.7508/gjesm.2016.01.003
2. Carugati, L., Gatto, B., Rastelli, E., Lo Martire, M., Coral, C., Greco, S., & Danovaro, R. (2018). Impact of mangrove forests degradation on biodiversity and ecosystem functioning. Scientific Reports, 8(1), 1–11. https://doi.org/10.1038/s41598-018-31683-0
3. Florida Atlantic University. (2018). Humanmade mangroves could get to the “root” of the problem for threats to coastal areas. ScienceDaily. Retrieved February 20, 2020, from https://www.sciencedaily.com/releases/2018/08/180829115627.htm
4. Hapsari, K. A., Jennerjahn, T. C., Lukas, M. C., Karius, V., & Behling, H. (2019). Intertwined effects of climate and land use change on environmental dynamics and carbon accumulation in a mangrove-fringed coastal lagoon in Java, Indonesia. Global Change Biology. https://doi.org/10.1111/gcb.14926
5. Henderson, C. J., Gilby, B. L., Schlacher, T. A., Connolly, R. M., Sheaves, M., Flint, N., Borland, H. P., & Olds, A. D. (2019). Contrasting effects of mangroves and armoured shorelines on fish assemblages in tropical estuarine seascapes. Ices Journal of Marine Science, 76(4), 1052–1061. https://doi.org/10.1093/icesjms/fsz007
6. Kodikara, K. A. S., Mukherjee, N., Jayatissa, L. P., Dahdouh‐Guebas, F., & Koedam, N. (2017). Have mangrove restoration projects worked? An in-depth study in Sri Lanka. Restoration Ecology, 25(5), 705–716. https://doi.org/10.1111/rec.12492
7. Nagelkerken, I., Blaber, S. J. M., Bouillon, S., Green, P., Haywood, M., Kirton, L. G., Meynecke, J.-O., Pawlik, J., Penrose, H. M., Sasekumar, A., & Somerfield, P. J. (2008). The habitat function of mangroves for terrestrial and marine fauna: A review. Aquatic Botany, 89(2), 155–185. https://doi.org/10.1016/j.aquabot.2007.12.007
8. Rante, A. (2019, December 12). A stilt mangrove tree in a protected area on Semama Island in East Kalimantan. Supertrees: Meet Indonesia’s mangrove, the tree that stores carbon. [Image].Vox. Retrieved February 20, 2020 from https://www.vox.com/2019/12/12/21009910/climate-change-indonesia-mangroves-palm-oil-shrimp-negative-emissions-blue-carbon
9. Rante, A. (2019, December 12). In the water lapping at mangrove roots, young fish and plankton take refuge from predators. Supertrees: Meet Indonesia’s mangrove, the tree that stores carbon. [Image].Vox. Retrieved February 20, 2020 from https://www.vox.com/2019/12/12/21009910/climate-change-indonesia-mangroves-palm-oil-shrimp-negative-emissions-blue-carbon
10. Sarker, S. K., Matthiopoulos, J., Mitchell, S. N., Ahmed, Z. U., Mamun, Md. B. A., & Reeve, R. (2019). 1980s–2010s: The world’s largest mangrove ecosystem is becoming homogeneous. Biological Conservation, 236, 79–91. https://doi.org/10.1016/j.biocon.2019.05.011
11. Thompson, B. S., & Rog, S. M. (2019). Beyond ecosystem services: Using charismatic megafauna as flagship species for mangrove forest conservation. Environmental Science & Policy, 102, 9–17. https://doi.org/10.1016/j.envsci.2019.09.009
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