Mangroves protect shorelines, store carbon, and support the livelihoods of communities in their vicinity. These coastal marine forests bridge the space between land and sea, attracting tourists and creating habitat for young fish. Their biggest enemy? Shrimp and the farms that grow them.
Why are mangroves so important?
Mangroves are major absorbers of carbon dioxide. They grow at the interface between the ocean and land, by rooting themselves in salty and tidal waters they can capture up to four times as much carbon as forests on land. They grow fast and trap carbon for longer than typical trees because the tides bring in regular nutrients and the soil they grow in is shackled by their interlocking roots. However, mangroves don’t just sequester carbon. These tangles of coastal trees trap sand and debris in their roots stabilizing entire shorelines. This ecosystem service is particularly important as climate change alters weather patterns and causes more violent and devastating storms, which can lead to destruction in coastal communities. Mangroves provide jobs and livelihoods, their intricate webs of roots protect important species like bonefish which draw in tourism and provide food and economic opportunity in many Caribbean countries.
Figure 1. Mangrove forest.
What are major threats to mangroves?
Despite the clear benefits of mangroves they are being lost at alarming rates. Between 35% to 50% of all mangrove forests in the world are estimated to have been lost in the last 60 years. Many mangrove forests have been developed for swanky resorts and rice farms. The most insidious danger, though, is aquaculture. Specifically, shrimp farming.
Why is shrimp farming so bad for mangroves?
Shrimps thrive in warm water, so shrimp farming is common in tropical and coastal areas where farmers can access ocean water for the large ponds. This puts them in direct conflict with tropical, coastal trees like the mangrove.
The harm that shrimp farming does to mangroves is a combination of many factors. The most obvious is clearing forests to make way for the shrimp ponds. When removed, mangroves stop sequestering carbon, and release carbon that may have been stored for centuries.
Shrimp farms also pollute, contaminating nearby ecosystems, including the mangroves that remain. This may only decrease the productivity of the ecosystem, but in the worst case can harm the trees enough that previously manageable weather and pests now become fatal. Finally, once these farms aren’t in use anymore mangroves can have trouble growing back in poisoned soil– permanently destroying the ecosystem.
What can be done?
There are many ways to address the decline in mangroves. But, it’s complicated. People rely on shrimp farming to make a living. However, conservation is possible without harming livelihoods. Some strategies involve increasing the productivity of individual shrimp ponds so less land is needed to produce the same amount which reduces the amount of mangroves destroyed. Another solution is to promote a transition towards lifestyles rooted in self-sufficiency or tourism based practices that rely on the mangrove ecosystem instead of being rooted in the destruction of the mangroves. When people’s own livelihoods are intertwined with the environment, they are more inclined to protect it. For example, in Curaçao native islanders are planting mangroves and leading kayak tours that highlight the trees and the host of life they support.
Land use is only one piece of the puzzle. Development in the past century has destroyed swaths of mangroves which must be restored to regain vital carbon sequestration and coastal protection. These types of projects are successful when they are viable, rooted in knowledge, and maintained. Local knowledge combined with modern technology can pave a way for projects that are attuned to how the habitat once existed and its recreation. Additionally, the project’s location must let, in this case, the planted mangrove to thrive. This involves removing pollutants that may have accumulated from the shrimp farms and taking down buildings and structures that may disrupt growth. Finally, a component that is often overlooked in restoration projects is long term monitoring. These replanting may fail one, three, or seven years down the road due to inattention and a lack of engagement with the project. A lack of engagement would also prevent future projects from learning from the mistakes of current projects.
What has been done/ is being done currently?
An aquaculture scientist from Conservation International has been working to address the issue of mangrove destruction. Dane Klinger, has found that there are ways to use modern technology like aerators (tubes that add air to the ponds) and water quality sensors that can help shrimp farmers maintain the best conditions for their growing shrimp. This increases the productivity of each pond. He then encourages farm owners to convert some of their land into restored mangrove forest. This approach is being attempted in both Ecuador and Indonesia right now.
Figure 2. Shrimp ponds in Belize.
Righting wrongs, a project in Senegal is aiming to restore mangroves in order to protect farmland. Without a protective barrier of coastal mangroves, salt water creeps further through the soil and prevents crops from growing. But the roots of healthy mangroves act as a filter. The project has 79 million mangrove over 10,000 hectares in 350 different villages. This is the largest mangrove restoration project in the world and has had a lasting impact not only on the environment but on the communities in Senegal.
What can you do?
Eat sustainably. Look for shrimp that are certified sustainable by councils like the Aquaculture Stewardship Council (ASC) and the Marine Stewardship Council (MSC). Avoid shrimp from specific countries like India, Indonesia, and Mexico which are known to have environment-harming practices, especially if they aren’t certified. It is possible to protect mangroves against shrimp farming but it requires many approaches.