Aldabra Atoll’s mangrove extent has increased by 60 ha over the past 20 years but faces threats |19 August 2021
Aldabra’s mangroves have increased by a size equivalent to 50 football fields over the past 20 years. These forests are Seychelles’ largest and are a key component of the country’s blue carbon © Annabelle Constance
The extent of mangroves on the Unesco World Heritage Site of Aldabra Atoll has increased by 60 ha (approximately 50 football fields) at a rate of 0.23% per year since 1997, according to a new study.
Using satellite imagery captured over Aldabra from 1997 to 2018, the paper compares the mangrove extent on Aldabra over time.
The results highlight the importance of protection of this valued habitat, the largest mangrove extent of the Seychelles, and underscores the ecological importance of Aldabra on a regional level.
Mangrove forests are vital for the conservation of biodiversity, protection of coastlines, and carbon capture but are decreasing globally at a rate higher than other tropical forests.
On Aldabra, mangroves have been strictly protected since 1976, and cover more than 11% of Aldabra’s total land area – one of the highest proportions of mangrove cover worldwide relative to island size.
Despite being protected, Aldabra’s mangroves are vulnerable to climate change impacts reported within the Indian ocean. Sea level rise impacts mangroves through erosion, decreasing the oxygen available for the plants to breathe and promoting toxic soil growing conditions for the plant. Combined with an increase in sea level, increases in wave power will lead to a shift in the zone of wave activity on the coast, likely to cause twice as much land inundation on these atoll islands as predicted by sea level rise effects alone.
Results of the study by researchers from the University of Zurich and the Seychelles Islands Foundation (SIF) found that the change in mangrove forest was variable around the coastline and connected to the existing extent.
Commenting on the paper, lead author and University of Zurich / SIF researcher Annabelle Constance stated “while we know a lot about the importance of mangroves, we still need to better understand the factors that influence their extent, which in simple terms means where mangrove forests have grown, died or remained stable over time. In that regard, our study is helping to better protect these valuable forests by highlighting what impacts their extent”.
Adding to her comments, SIF’s chief executive, Dr Frauke Fleischer-Dogley, stated “over just 20 years the increase in mangrove area found on Aldabra Atoll is slightly larger than the whole district of Grand Anse Praslin. This remarkable increase shows the potential of our protected areas in Seychelles to raise finance as blue carbon capital that will not only fund our work to manage our protected areas but also assist the local community to develop sustainable business models based on our intact environment”.
The researchers also found an effect of the wave power (transfer of energy by waves) on mangrove extent stability. Lower wave power values were recorded for stable mangrove areas than for areas that had gained or lost mangroves from 1997 to 2018.
These results confirm that local mangrove extent are vulnerable to threats of sea level rise that will likely exacerbate the impact of waves on atolls by allowing larger, more powerful waves to reach the coastline. With the latest Intergovernmental Panel on Climate Change report further confirming the global impacts of climate change and the urgency required to reduce greenhouse gas emissions as well as adapt, this paper underlines that while local and national conservation efforts are working, international cooperation and meaningful agreements are desperately needed.
The paper can be accessed at: https://www.sciencedirect.com/science/article/pii/S2351989421001141
Press release from SIF
