Sumedha B S, Bangalore University
Introduction:
Mangroves trees typically grow along tropical coastlines. They are rooted in salty sediments. The upper branches and leaves grow above the waterline, while the lower trunk and a large system of aboveground roots (prop roots) are often inside the seawater.
Mangrove forests are vanishing at an alarming rate worldwide. Global mangrove degradation leads to the loss of the fauna associated with it. This fauna is essential for ecosystem balance. The ecological functions they offer depends on the relationships between their plant and animal components. A viable mangrove forest cannot exist without a strong community of invertebrates sustaining it.
Lack of fauna threatens mangroves:
The Mangrove ecosystems support many invertebrates but, the effect of deforestation and pollution on the functional diversity of this fauna was never assessed before. No data is available of how the impact of deforestation affects the diversity of the invertebrate fauna, vital for its functioning.
To address this question, marine ecologists conducted an international study. They assembled the dataset of 155 mollusc and 209 crustacean species. It was collected from 16 mangrove forests around the world. These were categorized into 64 “functional groups” based on behavioural traits and feeding habits. For each site, they calculated the functional redundancy, taxonomic distinctness, functional vulnerability and functional richness.
The functional redundancy of the fauna refers to the mean number of species that have similar functions in an assemblage. The functional redundancy of invertebrates in mangrove forests is extremely low globally. The only exception is Southeast Asia. So, even a modest loss of fauna has negative consequences for the ecosystem. If a forest has high functional redundancy, when one species is lost, another can fulfil its function. When compared with other ecosystems, mangroves have the lowest fauna serving the identical ecological function. More than 60% of the tested sites showed no functional redundancy. Mangrove forests are one of the most delicate ecosystems of the world due to the low redundancy of invertebrates.
The invertebrates in a mangrove forest are essential for providing oxygen to the roots and also nutrient cycling. The mangrove forests heavily depend on the local invertebrate fauna.
The few small mangrove patches in Hong Kong and Mozambique having a higher number of invertebrates serve as important biodiversity reservoirs for future conservation efforts. The findings of this study were published in The Proceedings of the National Academy of Sciences.
Conclusion:
Studying the functional diversity of the local fauna is vital for determining the susceptibility of mangrove forests to environmental change. Knowing this can be used for mangrove conservation planning.
The health and resilience of mangrove forests around the world have been assessed by measuring the overall increase in area. But these studies don’t consider the real vulnerability and functionality of these forests.
In this study, it was showed that faunal functional diversity may be an improved approach to mangrove resilience than the forest size measurement.
So, mangrove rehabilitation and conservation projects need to consider not only the increase in size but also the redundancy of the local faunal component. Mangroves are among the most vulnerable ecosystems on the planet and steps for conservation must be taken seriously.
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References:
- Cannicci, S., Lee, S. Y., Bravo, H., Cantera-Kintz, J. R., Dahdouh-Guebas, F., Fratini, S., Fusi, M., Jimenez, P. J., Nordhaus, I., Porri, F., & Diele, K. (2021). A functional analysis reveals extremely low redundancy in global mangrove invertebrate fauna. Proceedings of the National Academy of Sciences, 118(32). https://doi.org/10.1073/pnas.2016913118
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