Ecology Hazards Human impacts Pollution

The disastrous effects of an oil spill: A tale of Mauritius vs. MV Wakashio

Reference: Seveso, D., Louis, Y. D., Montano, S., Galli, P., and Saliu, F. (2021). The Mauritius Oil Spill: What’s Next? Pollutants1(1), 18-28.

The MV Wakashio accident: What happened?

Oil leaking from the MV Wakashio, a Japanese tanker that ran aground on the reefs off the south-east coast of Mauritius island. Image from Greenpeace Africa.

Does Mauritius ring a bell? You may have heard of this tiny Indian Ocean island last year, when its pristine lagoons were hit by the worst oil spill it had ever known, making news all around the world. On July 25, 2020, the MV Wakashio, a 300 m long Japanese tanker ran aground on a barrier reef off the south-east coast of Mauritius, and two weeks later, it began leaking this fuel into the sea. According to official statements, it carried around 4 million liters of fuel (an Olympic-sized swimming pool has a volume of 2.5 million liters – about half that). The disaster prompted a state of environmental emergency and a cry for international aid to help the small country contain the spill.

How was the oil spill contained?

Citizens of Mauritius actively participating to contain the spread of the oil spill by removing the oil accumulated on beaches and using an artisanal float made of dried sugarcane leaves. Images by Yohan Didier Louis and Rima Beesoo from Seveso et al. (2021).

Without thinking twice, the local population, with the help of non-governmental organizations (NGOs) and community service groups, aided in oil removal operations from the sea surface and along the coastline. In this massive citizen effort, about 2 million liters of contaminated liquid waste (oil mixed with seawater) was effectively cleaned from the coastline. While clean-up operations are still ongoing, such an ecological disaster has affected highly sensitive sites around the island, including marine protected areas, nature reserves, and mangrove forests, and it has severely impacted the local communities that rely on them. Part of the affected shoreline has been restricted to fishing and recreational activities, and although no trace of oil is visible on the sea surface after the clean-up efforts, there are still large accumulations in the mangrove forests, which may have long-term consequences.

How did the oil spill affect the island’s mangroves?

Oil deposits on mangrove roots and plant surfaces block the breathing surfaces of mangrove trees, and prevent smaller trees from growing further. Image by Yohan Didier Louis from Seveso et al. (2021).

Mangroves have been particularly impacted by the oil spill in Mauritius, which raises concerns because this sensitive ecosystem is an important nursery ground for various marine species such as fish and shellfish. When the oil is released into the coastal waters and reaches the shore, it deposits on the sediments that cover the roots of mangrove trees and sticks on the plant surface. Not only does the oil stick to the breathing surfaces of the mangrove trees and their surrounding sediments, but it also suffocates the tiny organisms that live in burrows and root hollows. Shorter plants and animals die mostly within days, while taller trees, where oil only deposited on their roots and sediments may survive for 6 or more months before eventually dying. To help monitor and restore the affected mangrove communities, a working group was set up, comprised of local officers, researchers, and scientists, as well as foreign scientists from Japan and the United Nations. The aim was to assemble a team with diverse expertise and local field experience to coordinate the monitoring and restoration efforts, including potential mangrove farming, but to date, discussions are still ongoing.

How did the oil spill affect other marine communities?

A dolphin washed on the beach 3 weeks in the same region where the oil spill occurred. 51 dead dolphins were found following the oil spill. Image from Greenpeace Africa

In addition to mangroves, oil spills can have impacts on other marine organisms, which range in size from small microorganisms to large mammals. Corals can be particularly vulnerable, because their reproduction can be severely impaired. However, the annual mass coral spawning, which is the period where the corals release their eggs to be fertilized for reproduction, has been observed in the impacted area at the beginning of November 2020 like previous years. This means that the oil spill has fortunately not altered the timing of the release of eggs, for 2020 at least. On the other end, almost 20 days after the oil spill, 51 dolphins were washed ashore in the same region where the oil spill occurred. Although visual analysis of their skin, digestive and respiratory tract revealed no trace of oil, which initially dismissed the oil spill as the cause of their death, further analysis of samples in the laboratory found the presence of oil in 11 of the dead dolphins.

What does this mean for the economy and ecology of Mauritius?

Location of Mauritius (yellow square) in the Indian Ocean. Image modified from Wikipedia.org

Being a well-known touristic spot for leisure, sight-seeing, scuba-diving and water sports, Mauritius has one of the most famous coral reefs in the world, comprising a rich marine biodiversity. However, the island lies in an area with heavy shipping traffic, which can be a hazard for its biodiversity and natural treasures. The MV Wakashio accident is living proof of this. The effects could have been worst, but thanks to the mighty Mauritian citizens, who put their hearts and souls into helping contain the ecological disaster, and worldwide efforts, the oil spill was contained, and the damage minimized. However, the assessment of the impacts on marine life and the actions to restore the affected ecosystems are still in progress after several months, and will probably last for years.

If you are interested in learning more about the ongoing cleanup efforts, you are welcome to follow the Mauritian non-governmental organization EcoSud, and watch this youtube video.

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