ILOILO CITY, Philippines -- The oil sludge may not be visible anymore but scientists say the damage to marine resources of Guimaras Island has persisted two years after a massive oil spill ravaged the island.

The scientific studies showed abnormalities in the breeding and growth of mangroves, sea grass, marine animals and sea cucumbers, and attributed these mainly to the contamination of the marine environment by bunker fuel from the sunken M/T Solar I.

The studies, presented Thursday during the opening of the two-day Second National Conference on Solar I Oil Spill, showed the marine resources still suffered from stress brought by the contamination despite showing signs of recovery.

"There are good signs showing recovery but the studies show continued stress to marine resources brought by the contamination," University of the Philippines-Visayas (UPV) Oil Spill Response program manager Dr. Resurreccion Sadaba told the Philippine Daily Inquirer (parent company of INQUIRER.net).

Around 100 scientists, government officials and agencies that responded to the disaster attended the conference held at the UPV campus recently.

More than 2.1 million liters of bunker fuel spilled from the M/T Solar 1, which was chartered by Petron Corp., after it sank in stormy seas southeast off Guimaras on on August 11, 2006. Solar 1 was travelling from Bataan to Zamboanga.

It was considered as the country's worst oil spill, with around 8,580 families or 42,000 persons affected in Guimaras and some parts of Iloilo.

It also contaminated around 65 barangay (villages), according to Rosario Cabrera, Western Visayas director of the Office of Civil Defense.

The studies were mostly undertaken at the 1,143-hectare Taklong Island National Marine Reserve (Tinmar) in Nueva Valencia town, the hardest hit among the island-province's five municipalities.

Sadaba, who chaired the conference, said his team through six monitoring stations in the Tinmar mangroves found significant reduction in canopy cover and leaf size of some mangrove tree species.

The study made between October 2007 and September 2008 in six monitoring stations also showed tree deformities.

The mangroves were the worst hit among the contaminated marine resources.

The studies noted that the sodium-potassium balance in oiled areas was higher compared with areas unaffected by the oil spill, Sadaba said.

He also raised concern over the possible entry of heavy metals like copper, lead, nickel and zinc, which were found to have a higher concentration in contaminated areas, to the food chain.

Sadaba said the indicators of recovery included a decreasing rate of litter fall closing to normal rates.

But he said it was too early to conclude that the trees would fully recover.

Several studies, such as those conducted by Marie Frances Nievales and Dr. Rene Rollon, also found the decline in seagrass cover and the number of marine animals, including sea cucumbers and shells.

Several studies also showed significant drops in fish size and abundance but the scientists said they could not attribute the decline directly to the oil spill because these could be caused by over fishing and destructive fishing methods.

The scientists recommended continued and long-term monitoring and research to track the reaction and adaptation of the marine resources to the contamination.