San Francisco, Dec 9 (IANS/EFE): Millions of starfish have died in recent months on the Pacific coast from Alaska to Mexico due to an epidemic across the ocean ecosystem caused by a pathogen agent that has been present for decades, recent research shows.

"It is not a new agent, and it might be a virus," Pete Raimondi, a professor in the Department of Ecology and Evolutionary Biology at the University of California at Santa Cruz, told Efe news agency.

"It has been on these coasts for at least 70 years. It is present in aquarium and museum specimens captured back then," the scientist said.

"What we need to find out now is why it has become so virulent," he said.

The outbreak of the starfish disease that has killed millions of these echinoderms, wiping out the species' populations, began around May and June 2013 on the coast of Washington state.

Starfish first lose their arms and then their tissue melts until they disintegrate.

Scientists have not yet identified the pathogen agent and although they believe it is present in other animals, like sea urchins, and in the sediment, so far it has only sickened and killed starfish.

"The fact that sea urchins may be vectors, but they are not affected, could hinder the starfish population's recovery because the agent will remain in the environment even if all starfish are killed," Raimondi said.

The massive loss of starfish is causing an increase in the population of mussels and sea urchins that are part of the creatures' diet, and a decrease in the numbers of other species that feed on starfish, thus creating an imbalance in the region's biodiversity.