impact

Coastal crisis: Mangroves at risk

Vegetated coastal habitats – mangrove forests, salt-marshes and seagrass meadows – have much in common with rain forests. These “blue forests” are hot spots for biodiversity, are known for their large carbon sink capacity, provide important and valuable ecosystem benefits to local communities – and they are experiencing a steep global decline.

However, while society is well informed of the benefits and threats associated with rainforests, there is a comparative lack of awareness of the status and benefits of vegetated coastal habitats.

Mangrove forest areas across the world have varying levels of pollution, but the situation is worsening. Mangroves are often used for dumping waste, including plastics that do not biodegrade, harming both these ecosystems and the species living there.

UN Environment mangrove ecosystems expert Gabriel Grimsditch says greater awareness of pollution and its impact is needed to help preserve coastal ecosystems.

 

Marine debris being cleaned from a tourist mangrove boardwalk in Bali, Indonesia (Sanur, 2017) © Steven Lutz, GRID-Arendal

“It is important to reduce and control land-based sources of pollution to mangrove forests to ensure that they continue delivering valuable ecosystem services to coastal communities and the world,” Grimsditch says.

According to the findings of a 2016 study by the United States National Oceanic and Atmospheric Administration:

Marine debris can cause the death of the animals that live in the mangroves and suppress the habitat. Mounds of rubbish in tidal channels can be detrimental to nearshore habitats and their associated species. Rubbish can inhibit tidal flushing and increase salinity levels, stressing the habitat. A direct local economic impact can be seen when word gets out that the mangroves are polluted and tourists stay away.

“The accumulation of marine debris can alter and degrade marine habitats through physical damage caused by abrasion, shearing, or smothering, and can change the physical and chemical composition of sediments,” says the study.

“Physical damage often impairs critical nurseries and refuges used by many different organisms that occupy these habitats and may reduce the quality of habitat for organisms whose daily activities (e.g., feeding, reproduction) require the use of specific environments.”

 

Marine debris can impact important breeding grounds and habitat for many reef fish, shrimp, birds and other animals (Panama Bay, 2017). © Rob Barnes, GRID-Arendal

 

A 2013 study on the effect of waste on mangrove functionality indicates that there may also be a potential link between mangrove pollution and carbon sequestration, as salinity stress can lead to mangrove mortality and less productive mangrove ecosystems.

A 2015 study of the impact of pollution on mangrove biodiversity in India concludes that chemical pollution, particularly the accumulation of toxic metals, could be a significant factor in reducing mangrove biodiversity.

The study found that more pollutants lead to a proliferation of pollution-tolerant mangroves as more sensitive species die off, leading to reduced mangrove biodiversity.

Five of the six mangrove habitats in the Indo-Malayan ecozone are shared by two or more nations. Regional cooperation for transboundary ecosystem management needs to be enhanced, says the study.

The UN Environment Assembly, the world's highest-level decision-making body on the environment, will gather in Nairobi, Kenya, from 4-6 December 2017 under the overarching theme of pollution.

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See our recent story: Mangroves in the spotlight

For more information: Gabriel.Grimsditch[at]unep.org