The formation of each marine hotspot, previously little understood, coincided with shifts of vast plates in the earth's crust, they said. Shallow seas suitable for thousands of species can emerge when continents start to collide.

"There have been at least three marine biodiversity hotspots during the past 50 million years," the international team of scientists wrote in the journal Science. Previously, biodiversity has been studied on shorter timescales.

"They have moved across almost half the globe, with their timing and locations coinciding with major tectonic events," they said. Some types of corals off Australia, for instance, had evolved from species off the Middle East.

The scientists, in the Netherlands, Australia, Spain, Britain, Malaysia, the United States and Panama, said they hope that better knowledge of the long-term formation and decline of "hotspots" could give clues to conservation needs.

The Mediterranean, linked to what is now the Indian Ocean region 40 million years ago when Africa was further south, died off as the main marine hotspot as Africa ploughed north. Some areas previously under water ended high in the Alps.

The Mediterranean was succeeded by a region between the Middle East and India as the main hotspot.

Lead author Willem Renema, of the Dutch National Museum of Natural History, said conditions for the current Indo-Australian Archipelago hotspot may be past their peak in a looming slow-motion collision as Australia moves north towards Asia.

Over the past five million years, mountains were forming such as in Papua New Guinea, as the continents crumpled together. Former huge corals off Sulawesi, Indonesia, had also been lifted out of the seas by the same huge forces.

"It's clearly something we can't do anything about, but the hotspot is more vulnerable than it used to be 6 or 10 million years ago," he told Reuters.

That was a hint that humans had to be careful about adding extra stresses, such as from global warming caused by burning fossil fuels in cars, factories and power plants, he said.

"It's more vulnerable so you have to be extra cautious about what you do ... it's closer to the edge than it was," he said.

Renema also said that candidates for the next global hotspot, in 25 million years or so, were likely to be off southern or eastern Australia.

-- For Reuters latest environment blogs click on: http://blogs.reuters.com/environment/ (Editing by Giles Elgood)