Mangroves in Danger: Lack of Invertebrates, Other Species That Threaten Plant Populations

As mangroves protect coastal areas and small marine animals by providing shelter and defense, they also need marine animals to survive. A new study shows that the lack of animals could threaten their population.

An international collaboration revealed that low functional redundancy, or the number of species that play the same ecological role, in this case for mangrove forests, suggests that even the slightest upset to their numbers could have far-reaching effects on the plants.

"Mangrove forests have been disappearing at alarming rates worldwide," says Shing Yip Lee, a professor from the Chinese University of Hongkong and an Adjunct at the Australian Rivers Institute in Griffith University in Australia, in a university press release. "The ecological functions and services they provide depend upon the relationships between their individual plant and animal components."

Additionally, Lee noted that mangrove forests will not thrive without a sufficient population of various invertebrates that help maintain them.

(Photo: ROSLAN RAHMAN/AFP via Getty Images)
People walk along with a trail platform at a mangrove forest of Sungei Buloh Wetland Reserve in Singapore on February 2, 2021.

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Understanding the Effect of Marine Animals on Mangrove Forests

Mangroves are widely known for their supporting effects on marine animals and invertebrates. However, the same can not be said in reverse. There is still little knowledge about the effect of anthropogenic events and deforestation on the population, resilience, and functional diversity of these plants. To try and gain insights on this problem, the international team of researchers compiled a huge data set involving 209 crustaceans and 155 mollusk species from 16 different mangrove forests across the globe. Their study revealed that a mangrove forest, compared to other ecosystems, has a significantly lower functional redundancy.

Professor Lee additionally explained that an ecosystem with a higher functional redundancy is like ecological insurance for the ecosystem. If one of the species fulfilling a specific role is eliminated or removed, another species can fill its place and keep the ecosystem viable.

In the case of the mangrove forests, the functional redundancy from invertebrates suggests that in the face of environmental changes driven by human activities, these ecosystems are in more danger compared to others.

Examining Functional Redundancy in Mangrove Forests

In their study "A Functional Analysis Reveals Extremely Low Redundancy in Global Mangrove Invertebrate Fauna," appearing in the latest PNAS journal, researchers grouped the species they found into 64 functional groups, divided by micro-habitat conditions, behavioral traits, feeding habits, and more. They also reported that more than 60% of the sites they surveyed had virtually no functional redundancy, meaning only one species fulfilled a specific role in these environments.

"Even a modest loss of invertebrate diversity could have significant consequences for mangrove functionality and resilience because invertebrates in a mangrove forest are crucial for nutrient cycling and for providing oxygen to the tree roots," Professor Lee explains.

In mangrove forests, the lack of invertebrate marine animals would disable the ecosystem, which would ultimately remove the natural defenses that protect coastal areas where humans live, as detailed in a 2020 study published on Nature. Also, researchers report that small parts of mangrove forests, such as in Hong Kong and Mozambique, could serve as biodiversity reservoirs that could fuel future conservation efforts.