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The best place to live underwater

Patterns of biodiversity used to trace the movement of hotspots are identified as sharing multiple species of marine life with the Indo-Australian Archipelago hotspot, which exists today. Evidence exists from the molecular genetics of mangroves. [Image courtesy of William Renema]

New York City has a population of more than 8 million people. The region of Japan known as Tokyo Metropolis has almost 13 million people living in its different neighborhoods. It seems like certain areas of the world just naturally attract large numbers of people, for one reason or another.

Similar to these busy cities, there are also regions of the world's oceans where large amounts of diverse marine organisms tend to gather. These "popular neighborhoods" of the underwater world are known to scientists as biodiversity hotspots, and they occur in areas of the ocean populated by large amounts of various marine species. Today, a biodiversity hotspot exists between India and Australia called the Indo-Australian Archipelago hotspot.

Recently, Willem Renema and colleagues from many different countries examined the history of these biodiversity hotspots in the world's oceans and came to some surprising conclusions. They looked at research that had been done regarding the past 50 million years of Earth's history, and identified three separate, major biodiversity hotspots had existed over those years. When they studied the history of these hotspots more carefully, they also noticed that these biodiversity hotspots did not always stay in one place, but actually moved around the world.

In fact, all three biodiversity hotspots from the past 50 million years slowly moved across the oceans, responding to the shifting of tectonic plates below the Earth's surface, the researchers say. The location of each of those specific hotspots corresponds with major historic collisions between tectonic plates -- the causes of earthquakes. So it seems that, historically, marine organisms have been attracted to these earthquake events and tend to build large communities of diverse creatures around them.

The researchers also noted that the ages of the groups of marine organisms found in today's biodiversity hotspot, the Indo-Australian Archipelago hotspot, are much older than researchers previously thought. This fact gives more support to the idea that these hotspots have moved around over the years.

The apparent link between patterns of biodiversity and changes in the environment suggest that biodiversity probably develops on time scales that are much longer than the ones normally used to study diversity on Earth. But this new information from Renema and colleagues may help us understand how marine biodiversity will develop in the future.

This Review appears in the 1 August issue of the journal Science.