When the cargo ship MV Wakashio ran aground on a coral reef on the southeast tip of Mauritius, in the Indian Ocean almost exactly a month ago, it unleashed a vast oil spill. The Japanese-owned vessel held 200 tonnes of diesel and 3,900 tonnes of fuel oil, an estimated 1,000 tonnes of which leaked into the sea when the ship’s hull cracked on 6 August. It is the first reported spill of a new type of low-sulfur fuel that has been introduced to reduce air pollution. The spill has left a 15-kilometre stretch of the coastline — an internationally recognized biodiversity hotspot — smeared with oil.

Jacqueline Sauzier, president of the non-profit Mauritius Marine Conservation Society in Phoenix, has been helping with volunteer efforts to contain the spill. She spoke to Nature about how the clean-up is progressing.

What ecosystems have been affected?

When you look at images in the media, it can feel like the whole of Mauritius is under oil. But the oil reached only 15 kilometres of the 350-kilometre shoreline, so it could have been much worse.

Unfortunately, there are a lot of environmentally sensitive areas in the region affected. The ship ran aground off Pointe d’Esny and just to the north of Blue Bay Marine Park. These sites are listed under the Ramsar Convention on Wetlands of International Importance as biodiversity hotspots. Ocean currents carried the oil northwards, so fortunately there’s none in the Blue Bay Marine Park, but the mangroves on the shoreline north of Pointe d’Esny have been covered. This will definitely have an impact, because mangroves are the nursery of the marine environment.

The Île aux Aigrettes, a small island near the wreck, has also been affected. The island is home to vulnerable pink pigeons (Nesoenas mayeri) and other native birds, and Telfair’s skink (Leiolopisma telfairii). The Mauritian Wildlife Foundation in Port Louis was already working to restore the island’s unique plants and remove invasive species. The oil didn’t go onto the island itself, but chemicals might have seeped into the corals and fumes from the spill could also have an impact.

Two rivers open into the bay where the oil spill is. The brackish water at the mouths of the rivers is an important ecosystem, and the oil has managed to go up parts of the rivers. The oil slick also floated above a large and rare area of seagrass, which is home to seahorses. Although the oil didn’t touch the seagrass, we fear that chemicals in the water could reach them.

Are there particular species affected?

It is not one species that could be at risk. It is the whole ecosystem, because of the dispersal of water-soluble chemicals in the water. Filter feeders, such as corals and crustaceans and molluscs, are probably the first to be impacted. We haven’t seen lots of animals dying, but we will need to monitor for signs.

Bad weather over the past two weeks has also forced the ship against the coral reef. That pushed a lot of sand and broken coral over the reef into the lagoon, creating a sand bar just inside the reef. That could change the currents in the lagoon and will have an impact on coral growth.

The social impacts are also a big concern for us. Fishing communities living in the region cannot fish anymore, because the fish that have been caught contain high levels of arsenic.

Something that is also concerning is that we don’t know the possible long-term effects. The oil is a new low-sulfur fuel oil that is being introduced to reduce air pollution. This is the first time that type of oil has spilled, so there have been no long-term studies on the impacts.

What steps are being taken now?

As soon as the ship grounded, people started monitoring the quality of the water. So we have this baseline from before the spill and we know the target that we have to reach for remediation of the water.

Oil-spill experts are formulating a plan to clean the shoreline properly. The impact on the mangroves could be worse if the cleaning is done badly. It could also push chemicals into the sand, which could be released in warm weather a year or two from now.

The front part of the vessel has been tugged away to be sunk along the shipping route. This was the least bad option. The rear is still on the reef. It has been cleaned of fuel, but rust and paint could still cause damage. It’s also falling apart, which can break the coral

Can future spills be avoided?

We were lucky this time that the spill was small and the boat grounded when it did. First, if it had happened in April, we wouldn’t have been able to go out, because we were locked down because of COVID. Second, the cane harvest started at the end of June. So if the wreck had happened earlier, we wouldn’t have had the cane trash readily available to contain the oil.

The spill has opened people’s eyes. Mauritius lies near a shipping highway. Around 2,500 large vessels pass close to Mauritius every month. It is difficult to describe how very big the Wakashio is. From the shore, it’s as if something foreign is sitting on your veranda. But this is the third stranding that we have had in ten years. Each time, there is uproar from the community, saying large vessels are much too close to the island.

It is not the first time, but I really hope it is the last.

Source: BBC News