Damage to Chek Jawa's ecosystem in Pulau Ubin following last week's oil spill has, so far, been minimal, said the National Parks Board (NParks).

NParks' group director for conservation Wong Tuan Wah said that this was due to oil-absorbent booms - temporary floating barriers - that were set up soon after the spill. There are now two layers of booms protecting Chek Jawa, one of which was added last Friday. These booms absorb oil and serve as a physical barrier.

Still, Chek Jawa was flagged as a priority area in the wake of the spill, due to its rich biodiversity that could be affected by the leaked oil.

Said Mr Wong: "The oil sheen gets into the roots of mangrove trees, and affects their breathing pores."

The oil, he added, would also eventually seep into sand and mud, clogging up air pockets and suffocating creatures such as worms that live in the mud. "When the oil clogs up the holes, there will be a lack of air for marine creatures that live in the mud," he explained.

Yesterday, 15 NParks volunteers at Chek Jawa helped to mop up oil from the coastline in the morning and afternoon, while the tide was still fairly low.

There will be two more cleanup sessions today, at 9am and 1pm.

Last Tuesday, two container vessels collided off Pasir Gudang Port in Johor. This caused 300 tonnes of oil spillage after a bunker tank of one of the vessels was damaged.

Yesterday, the Chek Jawa volunteers were given a briefing before they put on protective jumpsuits, gloves and boots, and headed down to the coastline.

Hard at work under the sun alongside 30 of NParks' contract workers, they used oil-absorbent pads to soak up oil stains from rocks and mangrove trees. They also removed oil-stained seaweed and sand, and, with the help of spades, disposed them in yellow biohazard bags for incineration.

One of the volunteers yesterday afternoon was environmental sciences student Abel Yeo, 23, a nature guide-in-training at Sungei Buloh.

Mr Yeo said he felt a need to do something about the oil spill because of how close the spill was. "If it's closer to home, it affects us more. It affects our water quality, our biodiversity, our food supply."

A spokesman for the Agri-Food and Veterinary Authority said that as of last Friday, it had issued suspension of sales to 12 fish farms. The suspension will be in place until food safety evaluations are complete.

"Fish available in the market are safe for consumption," the spokesman added.

When The Sunday Times visited the Chek Jawa coast yesterday afternoon, there was a faint smell of petroleum in the air. Dark oil stains were visible on some mangrove roots, rocks and seaweed.

The Maritime and Port Authority of Singapore said in a Friday statement that "good progress has been made in containing and cleaning up the oil spillage". "No new patches of oil have been spotted along East Johor Strait," it added.

It noted that cleanup operations are ongoing at Changi Point Ferry Terminal, fish farms at Nenas Channel, and at Noordin beach on Pulau Ubin's northern coastline.

Oil spill response vessels, containment booms and spill recovery equipment were also deployed.

•Additional reporting by Audrey Tan