A joint research team by Japanese and Thai universities says it has become the world's first to find microplastics in the innermost part of coral, which shows the extent of plastic pollution of the ocean.

The team of Japan's Kyushu University and Thailand's Chulalongkorn University took samples of four coral species in waters off Thailand in 2022.

The samples were analyzed with infrared rays using cutting-edge equipment provided by the Japan International Cooperation Agency.

The team says they found tiny plastic particles invisible to the human eye in all three parts of the coral -- the surface mucus, tissue and the skeleton.

The team says that once particles reach the skeleton, they could remain there even after the coral dies and to the tune of a thousand years.

Coral is an important part of the marine ecosystem, but it is susceptible to rising sea temperatures. The team's finding indicates coral is also affected by plastic pollution.

Professor Suchana Chavanich of Chulalongkorn University Aquatic Resources Research Institute says that when microplastic levels are very high, coral will be bleached and could even die.

She also says the impact of microplastics can be lower than that of global warming, but when the two are combined, the impact could be more severe.