Threatened mangrove forests can regenerate carbon stocks to defer climate change

Joyce Chen ’23

mangroves
Figure 1. Mangroves are a vital ecosystem by storing carbon and hindering climate change.

Shrimp is currently in high demand and is the most-consumed seafood in the United States. However, farming shrimp comes with a large sacrifice. Shrimp are found in shrimp ponds, which are converted from mangrove forests; these forests are known for sequestering, or storing, carbon, thereby delaying global warming. With the expansion of shrimp aquaculture, mangrove forests have depleted significantly, losing up to 70% of ecosystem carbon. Moreover, they are one of the world’s most threatened ecosystems, with about 30 to 50% of cover lost over the past 50 years as a result of aquaculture and urbanization. 

To look into the carbon stocks found in mangroves, Angie Elwin and her team of researchers conducted an experiment on the carbon stocks of a mangrove forest and several abandoned shrimp ponds on an island in the Krabi River Estuary. The abandoned ponds were of ages 10, 15, and 22 years respectively.. Using biometric and soil coring methods to measure aboveground and belowground carbon levels, the team sought to understand the rate at which carbon was regenerating after the abandonment of the shrimp ponds. After testing the waters, researchers discovered that the carbon stocks in the ponds were on average 52% lower than those of the forests. The ponds aged 10 years after abandonment showed the highest loss in carbon, approximately 70% lower than the forests. Strangely enough, ponds aged 15 years after abandonment showed no significant difference in carbon stocks to the mangrove forests. The scientists also noticed that the depth of the soil in mangrove forests exceeded 3 m, while it varied in different ponds.The soil depth played a huge role in carbon sequestration, accounting for over 90% of carbon stocks. The shrimp ponds had 40% lower carbon stocks in soils compared to the mangrove forests, and the most recently abandoned ponds had up to 65% lower carbon stocks. But in spite of that, the ponds abandoned for over 15 years contained high amounts of carbon due to the greater soil depth; the upper soil layer of the older ponds resembled that of the mangrove forests. Furthermore, all of the ponds have showed signs of mangrove regrowth, but at varying rates. Ponds abandoned for more than 15 years had the highest sapling and seedling density, while recently abandoned ponds had the lowest. 

In conclusion, Elwin’s study showed that carbon naturally accumulates in the soil of the shrimp ponds overtime without restoration. However, it is still important to regulate shrimp aquaculture, as it is one of the leading causes of mangrove forest depletion. With that in mind, the regeneration and sequestration of carbon stocks in abandoned shrimp ponds will only increase overtime as the mangrove seedlings regrow, until they finally reach the carbon levels of the forests. 

 

References:

  1. E. Angie, et al., Preservation and recovery of mangrove ecosystem carbon stocks in abandoned shrimp ponds. Scientific Reports 9,  (2019). doi:10.1038/s41598-019-54893-6
  2. Image retrieved from: https://cdn.pixabay.com/photo/2013/01/03/12/36/everglades-73423__340.jpg

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